alkanes structure and naming (c) doc b(c) doc bDoc Brown's Chemistry  Revising Advanced Level Organic Chemistry

Doc Brown's Advanced Level Organic Chemistry Revision Notes

AN INTRODUCTION TO ADVANCED LEVEL ORGANIC CHEMISTRY

including a summary of FUNCTIONAL GROUPS and HOMOLOGOUS SERIES

 A summary guide to the Molecular Structure and Naming-Nomenclature of Functional Groups and selected Homologous Series in Organic Chemistry that you will encounter in most advanced pre-university courses

(c) doc b(c) doc bFollowing an introduction answering the question WHY is there such a range of organic molecules? there are sections of styles of representing the structure of organic molecules e.g. molecular formula and molecular structure. Then examples of functional groups, homologous series, general formula, displayed formula, graphic formula, molecular formula, skeletal formula, structural formula, empirical formula of molecules etc. are all explained with links to more examples of structure and naming and quizzes and reaction equations, reaction conditions and mechanisms. Alkanes, Alkenes, Alkynes, Aromatics-arenes, Halogenoalkanes, Alcohols (prim/sec/tert), Phenols, Ethers, Aldehydes, Ketones, Carboxylic acids, Acid/acyl chlorides, Acid Anhydrides, Acid/acyl Amides, Esters, Nitriles, Amines (prim/tert/sec), Quaternary ammonium salts, Nitro-aromatics, Diazonium salts and dyes, Sulphonic (sulfonic) acids and a variety possible Aromatic Compounds and Organic Nitrogen Compounds are also included. At the end is a guide to primary, secondary and tertiary structures i.e. the CLASSIFICATION system for haloalkanes, alcohols, amines and amides. These notes are designed for advanced level chemistry students e.g. UK based courses for AQA AS/A level chemistry. Edexcel AS/A level chemistry, OCR AS/A level chemistry A, OCR AS/A level chemistry B Salters



(c) doc bPage sub-index: INTRODUCTION * 9.1.1 Styles of structure and formula representation * 9.1.2 Alkanes, Alkenes, Alkynes, Aromatics-arenes, Halogenoalkanes, Alcohols (prim/sec/tert), Phenols, Ethers, Aldehydes, Ketones, Carboxylic acids, Acid chlorides, Acid Anhydrides, Amides, Esters, Nitriles, Amines (prim/tert/sec), Quaternary ammonium salts, Nitro-aromatics, Diazonium salts and dyes, Sulphonic (sulfonic) acids,  Appendix 1 Guide to primary, secondary and tertiary CLASSIFICATION. More examples, due to the variety of Aromatic Compounds and Organic Nitrogen Compounds, are on separate web pages.


A brief history of organic chemistry (advanced A level chemistry notes)

The word 'organic' historically refers to chemical materials pertaining to plant or animal or animal organisms. The term organic was used as a convenient classification for substances derived from plant or animal materials.

alcohols and ether structure and naming (c) doc b(c) doc bIn this sense organic substances go back to prehistoric times e.g. making wines by fermentation of sugary fruit materials (alcohol, ethanol solution) and the souring of wine to make vinegar (acetic acid/ethanoic acid solution).

Methods of using vegetable oils and animal fats to make soap have been known since Roman times,

and methods of applying the vegetable dye indigo and dyeing with madder root (alizarin) were also developed by both Roman and Egyptian civilisations. The production of dyed fabrics was an important commercial venture and some dyes were highly prized and the resulting fabrics very costly - purple only for very high status citizens! From these humble origins from the late 19th century to the present day the development and production of synthetic dyes shows no sign of slowing down!

By AD 900 the Islamic civilisation had developed a crude distillation process to increase the concentration of alcohol and produce oil of terpentine from pine resin. The words alchemy and chemistry are derived from Arabic words such as Al-Kimiya (which effectively means chemistry in Arabic today). The word alkaline is derived from the Arabic word Al-Qali which referred to substances derived from calcined ashes of the glass-wort plant that the Arabs used to make soap and glass. In medieval English it became 'alkali'. The names of substances like benzoin and benzene are derived from the Arabic phrase 'Luban Jawi' meaning substances derived from a natural 'aromatic' resin Arabic traders brought from Indonesia. Later benzoic acid was derived from benzoin resin and in turn benzene was synthesised from benzoic acid in the 19th century. In Victorian times dyes were made from aniline (phenylamine, aminobenzene), the Arabic word for dyes from indigo was annil. The word 'alcohol' is derived from the Arabic 'Al-khul' which mean body eating fluid! (it may also be the origin of the word ghoul!), but we are getting ahead of ourselves in the development of organic chemistry.

In the 16th and 17th century other products were made by pyrolysis e.g. the dry distillation of wood that yielded a variety-mixture of organic liquids including acetone (propanone). In the 18th century the technique of solvent extraction was used to obtain substances from plant and animal materials. In the years 1769-1785 the great Swedish chemist Scheele did many investigations that effectively prepared the way for the chemistry of studying biological products e.g. he isolated tartaric acid (2,3-dihydroxybutanedioic acid) as the sour taste of the grape, citric acid (2-hydroxypropane-1,2,3-tricarboxylic acid) from lemon, malic acid (2-hydroxybutanedioic acid) from apples, lactic acid (2-hydroxypropanoic acid) from sour milk, uric acid from urine and oxalic acid (ethanedioic acid) from wood sorrel, and he also prepared the latter by oxidation of sugar with concentrated nitric acid (a powerful oxidising agent). This was impressive work, but he had no idea what the molecular structure of these compounds was, but YOU can now work them out from the IUPAC systematic names in brackets.

Back to the late 18th century and early 19th century; from 1772-1777 the French chemist Lavoisier conducted some combustion analysis of organic compounds by measuring the amounts of water and carbon dioxide formed and was able to deduce the percentage of carbon and hydrogen in organic compounds. He produced the best results of his time, but they far from accurate, but it was recognised that organic compounds seemed to consist of carbon, hydrogen only, or these two elements combined with oxygen or nitrogen or both. unfortunately atomic theory and accurate atomic masses ('atomic weights') were still a few decades in the future.

The term 'organic'  as a branch of the study of chemistry, was used by the Swedish chemist Berzelius in 1807, and it was believed that these substance derived from once living material had some kind of 'vital force' associated with them. Organic compounds seemed more 'reactive', 'sensitive' or 'less stable' and so different from inorganic compounds e.g. they were combustible or readily transformed into different materials, especially by the application of heat and most organic compounds were liquids and low melting solids, compared to most inorganic compounds like salts which seemed so stable and high melting.

This doctrine of an essential vital force remained unchallenged until the German chemist Wohler, by chance discovery in 1828, that an inorganic salt (of non-plant/non-animal origin) was converted into a well known organic compound urea

All you do is evaporate ammonium cyanate solution ===> urea crystals;   NH4OCN  ===> CO(NH2)2

This is actually an (the first known?) example of an isomerisation reaction, in this case based on the formula CH4N2O

Clearly the inorganic salt had no 'vital force', and as Wohler said in a letter to Berzelius "I must tell you that I can prepare urea without requiring a kidney of an animal, either man or dog". Nearly the end of 'vital force' theory, but still no molecular structures known!

However, the term organic chemistry, has been universally accepted as the chemistry of carbon compounds bar carbon oxides and inorganic carbonates.

Further syntheses e.g. Kolbe's synthesis of ethanoic acid (acetic acid) from its elements in 1845, further proved that no vital force was needed to make vinegar, identical to that formed by the souring of fermented sugar solution!

The pioneering work of Lavoisier was continued by the German chemist Liebig (of condenser fame) who improved combustion analysis apparatus so that the  technique of burning organic compounds was producing quite accurate data by 1838. It actually took until 1911 via the work of the chemists like the Austrian Pregl to perfect the technique of semi-micro analysis on small samples of highly purified samples of organic compounds to give % composition to at least 3 significant figures. During the same period techniques for determining the percentage of nitrogen were also developed (by the French chemist Dumas 1830 and more accurately by the Danish chemist Kjeldahl in 1883 (a technique I was taught to do in the 1960s). This meant by the end of the 19th century the majority of organic compounds could now be analysed accurately, and from patterns in formula the idea of 'valency' or 'combining power' was beginning to shape (see work of Kekule below). Atomic masses e.g. of carbon, hydrogen, oxygen and nitrogen were now accurately known.

By the mid 19th century different substances with the same empirical formula were being recognised

e.g. alcohol (ethanol) and dimethylether (methoxymethane), both having an empirical formula C2H6O, but at that time, all they really knew that these compounds contained the same % of carbon, hydrogen and oxygen but were obviously different chemicals but of unknown structure.

From the increasing accurate and widening analysis of organic compounds, the idea of 'valency' ('combing power') of carbon, hydrogen, oxygen and nitrogen atoms was beginning to emerge and thanks to the brilliance of chemists like the German chemist Kekule, a solution to explaining the different formulae began to emerge.

Remarkably, as early as 1859 Kekule proposed that that carbon could form four bonds in a variety of ways, and added a similar idea for oxygen and hydrogen and came up with the following 'bonding' situations:

>C< (4 single),   =C= (two double),   -C (single plus triple),   -O- (two single),   =O (one double)  and   -H (one single)

Recognise this lot, not bad for a graphical representations of 1859, and it meant that Kekule could write out simple structures like

methane alkanes structure and naming (c) doc b,  carbon dioxide O=C=O ammonia ,  hydrogen cyanide (methanenitrile) H-CN

and the structures of hydrocarbons like ethane alkanes structure and naming (c) doc b  and   propane alkanes structure and naming (c) doc bwhich fitted the analytical data.

Therefore organic chemists now had a way of writing out formula and explore possible structures based on empirical formula analysis and of course be able to explain isomerism (different molecular structures with the same molecular formula).

e.g. alcohols and ether structure and naming (c) doc b  and  alcohols and ether structure and naming (c) doc b

We of course now take these structures to another level and draw electronic dot and cross diagrams, but they only emerged in the 1920s via the electron octet theory of compound structure!

So, it was only by the late 19th century the concept of 'homologous series' and 'functional group' were beginning to be recognised!

BUT, although structural formulae could now be correctly written down, the actual 3D shape of molecules was still a mystery.

Stereochemistry, 'three dimensional chemistry', didn't begin with organic molecules, but from 1812 to 1820 it was noticed that hemihedral quartz crystals seem to occur in two forms that were mirror images of each other. It was also demonstrated that each crystal form rotated plane polarised light in opposite directions. This occurs when molecular structures exhibit a centre of asymmetry. From 1820 to 1854 via the work of scientists like Louis Pasteur and Biot , crystals of some organic acid salts like ammonium tartrate could be separated into two forms with the same chemical formula, that were chemically and physically identical except that the solution of each form rotated plane polarised light in equal but opposite directions.

To explain the two different forms, which we now know as optical isomers (enantiomers), Kekule's valency theory offered a solution by presenting his 2D structures in a 3D way. The brilliant Dutch scientist van't Hoff proposed in 1874 that the four valencies of the 'central carbon' (we know call this the asymmetric or chiral carbon), pointed to the corners of a tetrahedron. Therefore with a molecule Cabcd, where a, b, c and d are different atoms or groups of atoms, it is possible to construct two models of the compound which are non-superimposable mirror image forms. These forms cannot have a plane of symmetry, whereas Ca4, Ca3b, Ca2b2, and Ca2bc all have a plane of symmetry . Unknown to van't Hoff, the French chemist Le Bel had come to the same theoretical proposition (hypothesis). We now know that from x-ray diffraction studies of optically active organic compounds, that both of these great scientists were absolutely correct, but that was about 40 years later in the early 20th century!

Now we can confidently draw structures such as  (c) doc b isomers for alpha amino acids, and deduce bond angles from electron pair repulsion theory, no problem!

So, by the end of the 19th century the basic structure of thousands of organic molecules was understood and ideas on the 3D structure of them too. Atomic masses were accurately known and methods of molecular mass determination were also developed so that the relationship between empirical formula and molecular formula were now clearly understood.

(c) doc bBy 1899 full commercial production of the sedative aspirin (acetylsalicylic acid, 2-ethanoylhydroxybenzoic acid), a medication used to treat pain, fever, or inflammation, was in full commercial production but the original molecules with these medicinal properties were obtained from plants such as willow and had been known in ancient Greece as early as 400 BC from the writings of Hippocrates, who describes the preparation of willow herb tea! This was one of many developments that 2300 years on from the ancient Greeks that has contributed to the development of the pharmaceutical industry.

The pain killer codeine is derived from morphine, the chief alkaloid molecule in opium. There are many instances where a whole series of drugs are developed from a starter molecule from a plant resource including analgesics, blood pressure controls, Statins to control cholesterol levels in the blood etc. etc. The skill of organic chemists is such that very complicated naturally occurring molecules can be synthesised in the laboratory by amazing multi-stage preparations from indigo like dyes to chlorophyll.

However, the spatial arrangement of atoms in organic molecules was not clear, so the idea of bond angles and 3D shape was still very much in its infancy and the propositions of van't Hoff and Le Bel, although correct, were not proven. The development of X-ray crystallography to get to the 3D molecular structure of organic molecules began in 1912-1914 with the work of Bragg (Cambridge, England) and the German Max von Laue. Initially they worked with inorganic crystals but as the x-ray diffraction analysis techniques improved, crystals of organic compounds were analysed. At the same time the electronic theory of atomic and molecular structure was developing and bond angles measured and compared with bonding theory predictions.

X-ray crystallography of biological molecules progressed e.g. with the remarkable and pioneering work of the English woman Professor Dorothy Hodgkin, who solved the structures of cholesterol (1937), penicillin (1946) and vitamin B12 (1956), for which she was awarded the Nobel Prize in Chemistry in 1964 (apart from mother Marie and daughter Irene, the Curies were the only other women to get a Nobel prize in chemistry). In 1969, she succeeded in solving the structure of insulin, on which she had  worked for over thirty years!

In 1952 Rosalind Franklin and others working at Kings College, London and Cambridge, obtained crucial x-ray diffraction photographs (crystallographic data) that would help lead to the recognition of the double helix structure of DNA. Her work was not fully recognised at the time and she should have got a Nobel Prize in 1962 with the likes of Crick, Watson and Wilkins (who also used x-ray diffraction), but she tragically died of cancer in 1958 at the age of 37.

One of the problems was the complex mathematics needed to analyse x-ray diffraction data. What might take months in the 1950s can be done in minutes today with modern high speed computers. IT is now a powerful too in the development of chemistry.

The structure of many essential molecules such as vitamins are known and many can be synthesised in the laboratory. Synthetic proteins can be made and manipulation of DNA genetic material is nothing short of amazing.

From the mid 19th century to the early 20th century, particularly in the USA, the commercial usefulness of crude oil was recognised and so the petrochemical industry was born from which, to this day, we derive a variety of hydrocarbon products ranging from fuels to polymers (the latter via alkenes from cracking) and a host of other organic molecules including the synthesis of many pharmaceutical products once derived from natural plant and animal sources.

In the late 19th century plastics were produced by modifying natural polymers e.g. celluloid by reacting cellulose from plants with nitric acid. The first truly synthetic plastic was the hard brown material known as Bakelite, patented in 1910. All the well known plastics like nylon, Terylene, poly(ethene) - discovered by accident in 1933, poly(propene), PVC, polystyrene, Perspex and polyurethanes were developed through 1930s to the 1960s. Crude oil has become the largest source of organic chemicals and we are very much dependent on its products.

World War II lead to many technological developments in radar and electronics. This in turn lead to major advances in spectroscopic techniques for investigating the structure of organic molecules. Techniques like infra-red spectroscopy and mass spectroscopy are quite limited but nuclear magnetic resonance spectroscopy (proton NMR and C-13 NMR) is the most powerful molecular technique apart from x-ray diffraction analysis.

1H proton NMR is so sophisticated now, you can deduce the whole structure of quite complex organic molecules from the NMR spectra alone, it is an amazing technique. I presume you still need x-ray diffraction analysis to get the full 3D structure?

Some of the most advanced chemical advances are now being made using computer databases of highly accurate 3D images of organic molecules. Even complex protein molecules like enzymes are being modelled and drugs can be designed to fit into the active site to inhibit their action, the basis of many medical treatments.


AN INTRODUCTION TO ORGANIC CHEMISTRY contd. (advanced A level chemistry notes)

More on WHY is there such a range of organic molecules and hence why a vast discipline of organic chemistry?

AND more on homologous series and functional groups.

  • There are many possible series of organic molecules, so why such variety?

  • Organic compounds belong to different families, though all organic compounds are based on carbon C, usually hydrogen H, and sometimes other elements such as oxygen, nitrogen, phosphorous and sulfur.

    • The chemistry of the oxides of carbon and carbonates is NOT considered part of organic chemistry.

  • Most food is chemically organic in nature, apart from some minerals, and many drugs and plastic materials are composed of organic molecules, consequently, organic compounds and organic chemistry is rather important to us!

  • The term organic compound comes from the fact that most of the original organic compounds studied by scientists-chemists came from plants or animals, i.e. of natural origin and contained the 'vital force' of mother nature!

    • Historically, for thousands of years, many organic compounds have been used indirectly in herbal preparations for healing and alleviating symptoms and in food materials such as honey.

    • Many natural products have proved precursors for the development of synthetic 'man-made' drugs manufactured by the pharmaceutical industry.

  • These days most organic compounds are produced and synthesised from raw materials, in particular the physical separation and chemical manipulation of the products of fractionally distilling crude petroleum oil.

  • However, this description of organic chemistry and its historical origins does NOT explain the vast range of organic molecules and their complex chemistry.

  • The principal reason why the range of organic molecules is primarily due to the fact that carbon atoms have the ability to link together by strong covalent bonds to form linear chains, branched chains and cyclic chains and with considerable numbers of rearrangements to make different molecules of the same formula (isomers).

    • Carbon is in Group 4 of the periodic Table with four outer electrons (2.4 or 1s22s22p2) which readily pair with electrons from an atom like oxygen or nitrogen to give four stable covalent bonds (maybe 4 single bonds, 2 single and a double bond, two double bonds or a triple and a single bond), either way, the normal valency (combining power) of carbon in organic compounds is four.

    • The property of forming chains is called catenation and the C-C bonds are generally strong giving rise to whole groups (homologous series) of stable organic molecules.

    • To add to the complexity and variety of organic molecules, carbon can also form stable bonds with other elements, especially ...

      • oxygen as in alcohols like ethanolwhich is used in fuels, as a solvent and combined with organic acids to make esters used in flavourings and perfumes.

      • nitrogen as in amines like ethylamine(c) doc b are organic bases and form alkaline solutions when dissolved in water.

      • nitrogen and oxygen in amino acids like aminoethanoic acid (c) doc bwhich is found combined with other amino acids in proteins.

      • halogens as in bromoethane (c) doc bis an 'intermediate' compound and used in the organic synthesis of more complex organic compounds.

      • and sulfur & phosphorus etc. by substituting a hydrogen atom with another element or group of atoms compared to hydrocarbon alkanes like butane (c) doc bwhich only consists of carbon and hydrogen atoms.

    • So, this leads to even more possible 'families' of organic compounds and many more individual different molecules.

    • There is no limit to the number of different organic molecules that can be made, though only a small percentage of them would be useful.

      • The molecular formula represents a summary of all the atoms in the molecule and a general formula sums up the formulae a series of compounds e.g. a homologous series of chemically similar compounds.

        • More on these terms later, but you need their basic definition to appreciate the next point I'm making.

      • Just to give you an idea of the limitlessness of organic chemistry, using some simple molecular formulae and general formulae, consider the table below of the number of molecules which can theoretically exist for a given molecular formula

        • The different structures with the same molecular formula are called isomers (see types of isomerism).

        • e.g. if n = 5 for the number of carbon atoms in the molecular formula you get ...

        • alkanes of molecular formula C5H12

        • alkenes/cycloalkanes of molecular formula C5H10

        • alcohols/ethers of molecular formula C5H12O

        • and amines of molecular formula C5H13N

          • Some of these numbers of these isomers (highlighted in blue) have been worked out using a computer program i.e. an algorithm is used to compute possible numbers of molecules of a given general formula given a set of rules based on valencies.

    • Number of carbon atoms n in the general formula below 4 5 6 7 8 9 10 11 12 examples of homologous series with this general formula
      CnH2n+2 2 3 5 9 18 35 75 159 355 alkanes
      CnH2n 3 5 13 27 66 153 377 ~915 ~2300 alkenes, cycloalkanes
      CnH2n+2O 7 14 32 72 171 405 989 ~2430 ~6070 alcohols, ethers
      CnH2n+3N 8 17 39 89 211 507 1238 3057 ? amines
    • As the number of carbon atoms increases the number of possible arrangement of the atoms increases dramatically even for molecules just containing carbon and hydrogen.

    • Once you substitute a hydrogen atom for another element or group of atoms, there is a bewildering number of possible molecular structures.

    • The fact that life, as far as we know it, is based on carbon chemistry, and we do not know of another element from which the same huge variety of stable molecules can be me made.

      • Even unstable organic molecules can be synthesised and manipulated in the laboratory and biochemistry is based on the thousands of molecules that exist in living systems e.g. sugars, proteins (tissue, enzymes etc.), RNA, DNA, fats like lipids etc. etc. etc.!!!.

        • In one of the simplest living cells like an E coli cell, there may be 5000 different compounds, most of them organic molecules! (e.g. as many as 3000 proteins and 1000 nucleic acids i.e. RNA/DNA molecules)

  • The compounds in each family have a similar chemical structure and a similar chemical formula and each family of organic compounds forms what is called a homologous series.

    • As pointed out, different families arise because carbon atoms readily join together in chains (catenation) and strongly bond with other atoms such as hydrogen, oxygen and nitrogen.

    • The result is a huge variety of 'organic compounds' which can be classified into groups of similar compounds i.e. these different homologous series.

  • A homologous series is a family of compounds which have a general formula* and have similar physical and chemical properties because they have the same functional group of atoms i.e. similar molecular structure.

    • e.g. C=C alkene, C-OH alcohol or -COOH carboxylic acid etc.

    • Usually, the addition of a -CH2- group gives the next member in the homologous series/

    • A functional group is an atom or combination of atoms which gives an organic molecule its distinctive and characteristic chemistry. This applies to all homologous series except alkanes which do not have a defined functional group.

    • The term 'functional' group is linked to the concept of a homologous series.

    • A homologous series is a group of molecules with the same general formula and the same functional group.

    • They have similar physical and chemical properties such as appearance, melting/boiling points, solubility etc. albeit with trends in physical properties e.g. increasing boiling point with increasing carbon chain length i.e. increase in molecular mass.

      • The terms higher/lower refer to a larger/smaller or longer/shorter carbon chains e.g.. the higher or lower number of CH2 groups in the carbon chain.

      • You should notice as you move from one member of a homologous series to the next, you add on an extra -CH2- unit.

  • The molecular formula represents a summary of all the atoms in the molecule e.g. butane is C4H10 and can be derived from a general formula - which is explained more in section 9.1.1 onwards.


 

9.1.1 Note on structure 'styles' of representation (advanced A level chemistry notes)


An empirical formula is the simplest whole number ratio of the atoms in a compound as found by experiment i.e. chemical analysis.

It gives no structural information and may or may not be the same as the molecular formula e.g. CH4 is both the empirical formula and the molecular formula of methane.

However, the molecular formula of the butane molecule is C4H10 but its empirical formula is C2H5.

The molecular formula of a glucose sugar molecule is C6H12O6 but its empirical formula is only CH2O !

The molecular formula will be simple integer multiple of the empirical formula ...

e.g. 2 x C2H5 gives C4H10    and    6 x CH2O gives C6H12O6

For calculations of empirical formula and molecular formula from chemical analysis and molecular mass ...

see Using moles to calculate empirical formula and deduce molecular formula of a compound/molecule


A molecular formula e.g. C3H6O2, gives a summary of all the atoms in the molecule, but gives no information on structure.

e.g. three atoms of carbon combined with six atoms of hydrogen and two atoms of oxygen.


A structural formula - minimal/abbreviated/shortened e.g. ethanol (c) doc bor(c) doc bcyclohexene, gives a 'limited' molecular structure view of a molecule but unambiguous if you know how to interpret the representation.

Some individual bonds may be shown (in cyclohexene) or non at all (ethanol).


The full graphical formula or full structural formula or full displayed formula e.g. (c) doc bshows all the individual atoms and bonds. However, it can be acceptable to show some side-chain groups in an abbreviated form e.g. methylpropane

where the side-chain methyl group may be written in the abbreviated form, but take care in exams, if unsure, clearly show ALL the atoms and bonds!


A structural displayed formula with full 3D spatial representation e.g. (c) doc bwhich shows the shape of the molecule and implies bond angles (in this case all are 109o). The 'dotted line' bond is behind the plane of the screen/paper/page and the 'wedge' bond is towards you. The other two thin line bonds are in the plane of the screen/paper/page etc. This gives a good impression of the real shape of the molecule in terms of the directional covalent bonds and all bond angles here are ~109o. The dotted line bond is now usually shown as a wedge pointing down away from the carbon atom.


A skeletal formula e.g. (c) doc bin which none of the H atoms bonded to carbon atoms are shown. The lines represent either carbon-carbon bonds (single, double or triple), but other lines are needed to show bonds to other atoms which are NOT carbon or hydrogen e.g. C-Cl in (c) doc band hydrogen atoms are shown if they are bonded to non-carbon atoms e.g. the C-OH in alcohols like(c) doc b.


A general formula sums up the formulae a series of compounds e.g. a homologous series of chemically similar compounds with closely related formulae e.g. the only difference may be more/less -CH2- groups in the longest carbon chain of the molecule.

There are many examples quoted throughout the rest of this page in the style CxHyOz etc. where x, y and z are integer variables like 1 (never shown), 2, 3 etc. but they are related for a particular homologous series e.g. for saturated non-cyclo alkanes by a general formula e.g.

CnH2n+2 for alkanes,

so that n = 1 generates the formula for methane CH4 and n = 5 generates the formula for pentane C5H12 etc.

CnH2n+1COOH is the general formula for monocarboxylic acids,

so that n = 0 generates the formula for methanoic acid HCOOH, the first aliphatic carboxylic acid

 and n = 4 generates the formula for pentanoic acid CH3CH2CH2CH2COOH, the 5th acid in the series.

(NOTE:  do not assume n always indicates the total carbon atoms in a molecule!)

However in all cases, the IUPAC systematic name is derived from the longest possible carbon chain in the molecule, so both meth... (for one carbon) and pent... (for five carbons) occur in the names of the examples above.


FUNCTIONAL GROUPS and HOMOLOGOUS SERIES

Summary of nomenclature, structure and representation in pictures-graphics


 

9.1.2 ALKANES or cycloalkanes HYDROCARBONS (saturated)

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

ANE, e.g. ALKANES, saturated hydrocarbons i.e. no double or triple bonds.

They can be linear, branched, cyclo, substituted etc. (see later - haloalkanes etc.) …

 (c) doc bbutane(c) doc bpentylcyclohexane(c) doc bcyclopropane

(c) doc b2,2-dimethylpropane(c) doc b2,2,3-trimethylbutane

Exemplar homologous series: General formula CnH2n+2 for non-cyclo alkanes (n = 1,2,3 etc.)

and general formula CnH2n for cycloalkanes (n = 3,4,5 etc.) isomeric with non-cyclo alkenes

further Notes and examples of the structure and nomenclature of alkanes

Multiple choice Quiz on naming alkanes

(c) doc b Type in an alkane name short answer QUIZ

Notes on selected reactions of alkanes from a mechanistic point of view but giving general equations and reaction conditions too

and ALKANES CHEMISTRY NOTES INDEX


 

9.1.3 ALKENE HYDROCARBONS (unsaturated)

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

 …ENE, ALKENES, unsaturated hydrocarbons with a carbon=carbon C=C double bond functional group (ene)

They can have more than one C=C, be linear, branched, cyclo …

(c) doc bpent-1-ene,(c) doc b3-ethylpent-1-ene,(c) doc bcyclobuta-1,3-diene

(c) doc bor(c) doc bbuta-1,3-diene(c) doc bcyclohexene

further Notes and examples of the structure and nomenclature of alkenes

Multiple choice Quiz on naming alkenes

(c) doc b Type in an alkene name short answer QUIZ

Exemplar homologous series: CnH2n for non-cyclo alkenes (n=2,3 etc. with one C=C bond)  isomeric with cycloalkanes

and CnH2n-2 for cycloalkenes (n=3,4,5 etc., and with one C=C bond)

Notes on selected reactions of alkenes from a mechanistic point of view but giving general equations and reaction conditions too


 

9.1.4 ALKYNE HYDROCARBONS (unsaturated)

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

 YNE e.g. ALKYNES, unsaturated hydrocarbons with a CC triple bond functional group (yne) e.g.

(c) doc b ethyne, and  (c) doc b propyne

Exemplar homologous series: CnH2n-2 for non-cyclo alkynes (with one triple bond)


9.1.5 AROMATIC HYDROCARBONS (unsaturated)

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

 'ARENES' are aromatic hydrocarbons with at least one benzene ring functional group e.g. …

(c) doc bor(c) doc bbenzene,(c) doc bor(c) doc bmethylbenzene

further Notes and examples of the structure and nomenclature of aromatic compounds

further Notes and examples of aromatics

(c) doc b Type in an aromatic name short answer QUIZ

Notes on selected reactions of aromatic compounds (arenes) from a mechanistic point of view but giving general equations and reaction conditions too


 

9.1.6 aliphatic/aromatic HALOGEN COMPOUNDS

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

Aliphatic: HALO… e.g. HALOGENOALKANES (HALOALKANES)

C-X halogen functional group where X = F fluoro…, Cl chloro.., Br bromo… or I iodo…

X is named as a prefix substituent in any type of organic molecule from alkanes to carboxylic acids.

(c) doc bchloromethane,(c) doc bbromoethane, (c) doc bdichlorodifluoromethane

(c) doc b1-bromo-1-chlorobutane(c) doc biodocyclohexane

(c) doc b1,2-dibromocyclopentane,(c) doc bchloromethylbenzene

or phenylchloromethane, which can also be classified as an aromatic compound

BUT the halogen is not attached directly to the benzene ring so it is not an aryl halide)

Exemplar homologous series: CnH2n+1X for non-cyclo saturated halogenoalkanes (X=F,Cl,Br,I and n=1,2,3 etc.)

and CnH2n-1X for saturated cyclohalogenoalkanes (n=3,4,5 etc. with one C-X bond)

  • A sub-CLASSIFICATION based on structural differences, which can have chemical consequences on e.g. rate of reaction or products formed in a reaction.

    • Halogenoalkanes are classified according to the atoms/groups attached to the carbon of the halogen atom X.

    • Primary halogenoalkanes have the structure R-CH2-X, R = H, alkyl, aryl etc. i.e. apart from chloromethane they have one alkyl/aryl group attached to the C of the C-X group.

      • e.g. chloroethane CH3CH2Cl

    • Secondary halogenoalkanes have the structure R2CH-X, R = alkyl or aryl etc. i.e. they have two alkyl/aryl groups attached to the C of the C-X group.

      • e.g. 2-bromobutane CH3CHBrCH2CH3 

    • Tertiary halogenoalkanes have the structure R3C-X, R = alkyl or aryl etc. i.e. they have three alkyl/aryl groups attached to the C of the C-X group.

      • e.g. 2-iodo-2-methylpropane (CH3)3CI

further Notes and examples of the structure, classification and nomenclature of primary, secondary and tertiary haloalkanes - 3 linked pages

Multiple choice Quiz on naming haloalkanes

(c) doc b Type in a haloalkane name short answer Quiz

Notes on selected reactions of halogenoalkanes (haloalkanes) from a mechanistic point of view but giving general equations and reaction conditions too

NOTE: Aromatic HALO ... ARENES (aromatic halogen compounds) have the halogen atom directly attached to the benzene ring.

(c) doc bchlorobenzene,(c) doc b1,4-dichlorobenzene,(c) doc bchloro-2-methylbenzene


 

9.1.7 ALCOHOLS (aliphatic, alkanols) and PHENOLS (aromatic)  

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

Aliphatic OH hydroxy functional group (ol) e.g. ALIPHATIC ALCOHOLS.

Aliphatic alcohols are classified as primary, secondary and tertiary.

You can have diols, triols etc, with 2,3 etc, OH groups.

If there is a 'higher ranking' functional group in the molecule the substituent OH is called by the prefix 'hydroxy' see * examples.

Primary aliphatic alcohols R-OH where R is alkyl

(c) doc bethanol,(c) doc bethan-1,2-diol

(c) doc bor(c) doc b3-methylbutan-1-ol

(c) doc b4-hydroxybutanoic acid*

Secondary aliphatic alcohols R-CH(OH)-R' where R or R' are both alkyl (or aryl):

(c) doc bpropan-2-ol,(c) doc bbutan-2-ol,(c) doc bcyclohexanol,(c) doc bpentan-3-ol

(c) doc bcyclopentanol(c) doc b2-hydroxybutanoic acid*

Tertiary aliphatic alcohols RR'R"C-OH where R,R' or R" are all alkyl (or aryl):

(c) doc bor(c) doc b2-methylpropan-2-ol,(c) doc b2-methylbutan-2-ol

(c) doc b or (c) doc b 3-methylpentan-1-ol

Exemplar homologous series: CnH2n+1OH for saturated non-cyclic aliphatic alcohols (n=1,2,3 etc.)

or the less informative CnH2n+2O isomeric with aliphatic non-cyclo ethers

and CnH2n-1OH for cycloalcohols (n=3,4,5 etc. with one C-OH)

Notes and examples of the structure and nomenclature of aliphatic alcohols/alkanols

  Multiple choice Quiz on naming alcohols

(c) doc b Type in an alcohol name short answer QUIZ

Notes on selected reactions of alcohols from a mechanistic point of view but giving general equations and reaction conditions too

AROMATIC PHENOLS ROH, R=aryl only,  when the -OH functional group is attached directly to a benzene ring the molecule is called a phenol.

If there is a 'higher ranking' functional group in the molecule the substituent OH is called by the prefix 'hydroxy' see * example.

(c) doc bor(c) doc bor(c) doc bphenol,(c) doc b2-chlorophenol,(c) doc b3-methylphenol

(c) doc b2,5-dichloro-4-methylphenol,(c) doc b3-hydroxybenzoic acid*


 

9.1.8 ETHERS

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

Alkyl/arylOXY…alkane/arene e.g. ETHERS which have the C-O-C linkage.

The smaller carbon chain with the oxygen atom, is given the prefix in the name alkyl/aryl..oxyane

(alkyl-O- groups like CH3-O- are called alkoxy groups).

(c) doc bmethoxymethane,(c) doc bmethoxyethane,(c) doc b2-ethoxypropane

(c) doc bethoxyethane,(c) doc b2-methoxypropane,

Exemplar homologous series: CxH2x+1-O-CyH2y+1 for saturated non-cyclo ethers (x or y =1,2,3 etc.)

or the less informative CnH2n+2O (n=2,3,4 etc.)  isomeric with non-cyclo aliphatic alcohols

or CnH2nO for cycloethers (n=2,3,4 etc. with one C-O-C linkage, non shown at the moment)

further Notes and examples of ethers and isomeric alcohols


 

9.1.9 ALDEHYDES and KETONES (a group of carbonyl compounds)

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

 …AL e.g. ALDEHYDES have the -CHO functional group at the end of a carbon chain e.g.

(c) doc bethanal,(c) doc bpropanal,(c) doc bor(c) doc b2-methylpropanal

(c) doc bbutanal,(c) doc bpentanal,(c) doc b2-methylbutanal

Exemplar homologous series: CnH2n+1CHO for aliphatic aldehydes (n=0,1,2 etc.)

or the less in formative CmH2mO (m=1,2,3 etc.) isomeric with ketones and saturated cyclic aliphatic ethers

further Notes and examples of the structure and nomenclature of aldehydes

  multiple choice Quiz on naming aldehydes/ketones

(c) doc b type in name short answer QUIZ on naming aldehydes/ ketones

Notes on selected reactions of aldehydes/ketones from a mechanistic point of view but giving general equations and reaction conditions too

ONE e.g. KETONES have the C-CO-C functional group linkage within the carbon chain:

(c) doc bpropanone,(c) doc bor(c) doc bbutanone,(c) doc bpentan-2-one

(c) doc b  or  (c) doc b   pentan-3-one

Exemplar homologous series: CxHxn+1-CO-CyH2y+1 for aliphatic ketones (x or y = 1,2,3, etc.)

or the less informative CnH2nO (n=3,4,5 etc.)  isomeric with aldehydes and saturated cyclic aliphatic ethers

 further Notes and examples of the structure and nomenclature of ketones

  multiple choice Quiz on naming aldehydes/ ketones

(c) doc b type in name Quiz on naming aldehydes/ ketones

Notes on selected reactions of aldehydes/ketones from a mechanistic point of view but giving general equations and reaction conditions too


 

9.1.10 CARBOXYLIC ACIDS

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

 …OIC ACID e.g. CARBOXYLIC ACIDS with the -COOH functional group, substituents quoted as prefixes (…dioic if 2 -COOH groups)

e.g. aliphatic carboxylic acids

(c) doc bmethanoic acid,(c) doc bpropanoic acid,(c) doc b*aminoethanoic acid

(c) doc b2-methylpropanoic acid,(c) doc b *2-hydroxybutanoic acid

(c) doc bpentanoic acid(c) doc b* ethanedioic acid

* examples of a dicarboxylic acids

If there is a 'higher ranking' functional group in the molecule the

substituent OH/NH2 is called by the prefix 'hydroxy/amino see * examples.

Exemplar homologous series: CnH2n+1COOH for saturated aliphatic mono carboxylic acids (n=0,1,2,3 etc.)

or the less informative CnH2nO2 (n=1,2,3,4 etc.) isomeric with aliphatic esters

aromatic carboxylic acids (-COOH directly attached to the ring)

(c) doc b * 3-hydroxybenzoic acid,(c) doc b2-ethanoylhydroxybenzoic acid (Aspirin!)

(c) doc b2-chlorobenzoic acid,   (c) doc b* benzene-1,2-dicarboxylic acid

(sometimes carboxylic rather than oic is used e.g. the dicarboxylic acids of benzene)

further Notes and examples of the structure and nomenclature of carboxylic acids and their derivatives

  multiple choice QUIZ on naming RCOOH acids/derivatives

(c) doc b Type in name short answer QUIZ on naming RCOOH acids/derivatives


 

9.1.11 ACID ANHYDRIDES

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

 …OIC ANHYDRIDE e.g. CARBOXYLIC ACID ANHYDRIDES with the RCO-O-RCO linkage e.g.

(c) doc bor(c) doc bethanoic anhydride

(c) doc bor(c) doc bpentanoic anhydride

Exemplar homologous series: (CnH2n+1CO)2O derived from aliphatic mono carboxylic acids (n=2,3 etc.)

further Notes and examples of the structure and nomenclature of carboxylic acids and their derivatives

multiple choice QUIZ on naming RCOOH acids/derivatives

(c) doc b Type in name short answer QUIZ on naming RCOOH acids/derivatives


 

9.1.12 ACID or ACYL CHLORIDES

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

 OYL CHLORIDE e.g. CARBOXYLIC ACID or ACYL CHLORIDES with the -COCl functional group e.g.

(c) doc bor(c) doc bpropanoyl chloride, (c) doc bbutanoyl chloride

(c) doc bor(c) doc bpentanoyl chloride,(c) doc bbenzoyl chloride

Exemplar homologous series: CnH2n+1COCl derived from aliphatic mono carboxylic acid chlorides (n=1,2,3 etc.)

further Notes and examples of the structure and nomenclature of carboxylic acids and their derivatives

multiple choice QUIZ on naming RCOOH acids/derivatives

(c) doc b Type in name short answer QUIZ on naming RCOOH acids/derivatives

Notes on selected reactions of acid/acyl chlorides from a mechanistic point of view but giving general equations and reaction conditions too


 

9.1.13 ACID AMIDES

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

 AMIDE e.g. CARBOXYLIC ACID AMIDES with the -CONH2 functional group e.g.

(c) doc bor(c) doc bethanamide,(c) doc bpropanamide

(c) doc bbutanamide,(c) doc bpentanamide,(c) doc bbenzamide

Exemplar homologous series: CnH2n+1CONH2 derived from aliphatic mono carboxylic acid amides (n=0,1,2,3 etc.)

further Notes and examples of the structure and nomenclature of carboxylic acids and their derivatives

and also other organic nitrogen compounds

multiple choice QUIZ on naming RCOOH acids/derivatives

(c) doc b Type in name QUIZ on naming RCOOH acids/derivatives


 

9.1.14 ESTERS

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

 alkyl/arylOATE e.g. ESTERS of CARBOXYLIC ACIDS derived from ALCOHOLS or PHENOLS.

Esters have the -COOC- linkage:

(c) doc bmethyl methanoate(c) doc bpropyl propanoate

(c) doc bethyl propanoate(c) doc bethyl benzoate

Exemplar homologous series: CxH2x+1-COO-CyH2y+1 simple saturated aliphatic esters (x=0,1,2, etc. and y=1,2,3 etc.)

or the less informative CnH2nO2 (n=2,3,4 etc.) isomeric with carboxylic acids

further Notes and examples of the structure and nomenclature of carboxylic acids and their derivatives

multiple choice QUIZ on naming RCOOH acids/derivatives

(c) doc b Type in name QUIZ on naming RCOOH acids/derivatives


 

9.1.15 NITRILES

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

The nitrile functional group consists of a carbon to nitrogen triple bond.

The name is based on the longest carbon chain, including the C of the nitrile group e.g.

methanenitrile, (c) doc b, (c) doc b, (c) doc b

ethanenitrile, (c) doc b, (c) doc b, (c) doc b, (c) doc b, (c) doc b, (c) doc b

propanenitrile, (c) doc b, (c) doc b, (c) doc b, (c) doc b, (c) doc b, (c) doc b

Exemplar homologous series: CnH2n+1CN derived from aliphatic mono carboxylic acid chlorides (n=0,1,2,3 etc.)

further Notes and examples of the structure and nomenclature of carboxylic acids and their derivatives

and also other organic nitrogen compounds


 

9.1.16 AMINES

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

PRIMARY AMINES have two hydrogen atoms and one alkyl or aryl group attached to the nitrogen to form the amine or amino group -NH2.

ALIPHATIC: methylamine (aminomethane), (c) doc b, (c) doc b, (c) doc b, (c) doc b

ethylamine (aminoethane), (c) doc b, (c) doc b, (c) doc b, (c) doc b

Exemplar homologous series: CnH2n+1NH2 for saturated mono primary amines (n=1,2,3 etc.)

SECONDARY AMINES have one hydrogen atom and two alkyl or aryl groups attached to the nitrogen

ALIPHATIC: dimethylamine, (c) doc b,(c) doc b, (c) doc b

ethylmethylamine, (c) doc b, (c) doc b

diethylamine, (c) doc b, (c) doc b

TERTIARY AMINES have no hydrogen atom and three alkyl or aryl groups attached to the nitrogen

ALIPHATIC: trimethylamine, (c) doc b ,(c) doc b

ethyldimethylamine, (c) doc b, (c) doc b

diethylmethylamine, (c) doc b ,(c) doc b

further examples of the structure and nomenclature of organic nitrogen compounds


 

9.1.17 QUATERNARY AMMONIUM SALTS

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

If all for hydrogens of an ammonium ion are replaced with alkyl or aryl groups then an ionic quaternary salt is formed.

e.g. the simplest is tetramethylammonium chloride, (CH3)4N+ Cl-


 

9.1.18 NITRO-AROMATIC COMPOUNDS

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

These have the nitro -NO2 group directly attached to the ring e.g.

nitrobenzene, (c) doc b; 1,3-dinitrobenzene, (c) doc b

 

2-methylnitrobenzene or 1-methyl-2-nitrobenzene, (c) doc b

and also other organic nitrogen compounds


 

9.1.19 DIAZONIUM SALTS and AZO DYES

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

Diazonium salts are formed when primary aromatic amines reaction with nitrous acid

The diazonium cation has a nitrogen - nitrogen triple bond system directly attached to the benzene ring e.g.

(1) (c) doc bfrom phenylamine+

(2) (c) doc bfrom 4-methylphenylamine

In alkaline solution these diazonium salts couple with phenols and aromatic amines to form azo dyes which have benzene rings linked with an azo -N=N- bond system e.g.

reacting (1) with phenol gives (c) doc b

reacting (2) with phenylamine gives (c) doc b

and also other organic nitrogen compounds


 

9.1.20 SULPHONIC ACIDS

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

Sulfonic acid molecules have a strongly mono-basic acidic group -SO2OH directly attached to the benzene ring e.g.

benzenesulphonic acid,(c) doc b(c) doc b ,(or benzenesulfonic acid)

2-, 3- or 4-methylbenzenesulphonic acid,(c) doc b, (c) doc b,(c) doc b (or ....sulfonic acid)


 

APPENDIX 1 A guide to primary, secondary and tertiary structures (mainly aliphatic compounds)

The CLASSIFICATION system for haloalkanes, alcohols, amines and amides

(advanced A level chemistry pre-university revision notes on functional groups and homologous series)

Functional group of the homologous series PRIMARY SECONDARY TERTIARY Comments
HALOALKANES (halogenoalkanes) The class of haloalkane can affect both the rate (reactivity) and mode (substitution or elimination) of the reaction
examples of haloalkanes (halogenoalkanes) (c) doc b

bromoethane

(c) doc b

2-chloropropane

(c) doc b

2-chloro-2-methylpropane

examples of haloalkanes (halogenoalkanes)
ALCOHOLS Phenols are NOT classified in this way. The ease of oxidation and nature of product is affected by the class of the alcohol
examples of alcohols alcohols and ether structure and naming (c) doc b

butan-1-ol

alcohols and ether structure and naming (c) doc b

propan-2-ol

alcohols and ether structure and naming (c) doc b

2-methyl-propan-2-ol

examples of alcohols
AMINES There are prim/sec/tert aliphatic (alkyl) or aromatic (aryl) amines. See also Note 3. below the table.
aliphatic amine examples (c) doc b

ethylamine

(c) doc b

ethylmethylamine

(c) doc b

triethylamine

aliphatic amine examples
aromatic amine examples (c) doc b

phenylamine

(c) doc b

diphenylamine

(c) doc b

N,N-diethylphenylamine

aromatic amine examples
acyl or acid AMIDES The amide group comprises an amine group attached to the C of a C=O carbonyl group, which gives it its own unique chemistry i.e. its neither an amine or an aldehyde or ketone!
examples of amides (c) doc b

ethanamide

(c) doc b

N-phenylbenzamide

(c) doc b

N,N-dimethylethanamide

examples of amides both aliphatic and aromatic
******************************* *************************** *************************** ******************************* ****************************************

 NOTES

  1. Abbreviations commonly used: prim or 1o (primary), sec or 2o (secondary) and tert or 3o (tertiary)

  2. R and R' do not have to be the same i.e. -R2 could mean -RR' and -R3 could mean -RR'R"

  3.   amines can form a quaternary ammonium ion

    • e.g. in the salt tetramethylammonium chloride, (CH3)4N+ Cl-

  4. -


LINKS TO OTHER ASSOCIATED PAGES 

 

KS3 SCIENCE QUIZZES ALPHABETICAL INDEX
GCSE grade 9-1 & IGCSE CHEMISTRY Doc Brown's Travel Pictures & Notes
ADVANCED LEVEL CHEMISTRY [SEARCH BOX] - see below
GCSE 9-1 Physics Revision Notes GCSE 9-1 Biology Revision Notes
All website content © Dr Phil Brown 2000 onwards. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries and references to science course specifications are unofficial. Email doc b: chem55555@hotmail.com

 Doc Brown's Chemistry 

*

 For latest updates see https://twitter.com/docbrownchem

 Have your say about doc b's website

TOP OF PAGE