alkanes structure and naming (c) doc b

1.1 The molecular structure and nomenclature - naming of alkanes

Part 1. ALKANES and the PETROCHEMICAL INDUSTRY

Doc Brown's Advanced A Level Organic Chemistry Revision Notes

alkanes structure and naming (c) doc bLots of examples of alkanes nomenclature structure All you need to know about naming alkanes How do you name alkanes? Nomenclature of substituted alkanes - examples of the structure of alkanes, naming alkanes, acceptable names, displayed formula of alkane molecules with names, graphic formula of alkanes, molecular formula of alkanes, skeletal formula of alkanes, structural formulae of the homologous series of alkanes, linear alkanes, branched alkanes, alkyl substituted cycloalkanes etc. Everything you need on the naming and structure of alkanes pre-university!

A basic introduction to the structure and chemistry of alkanes (including diagrams which haven't been repeated on this page).

A Level Organic Chemistry Part 1 sub-index:

1.1.1 Alkane nomenclature explained

1.1.2 Different ways of representing molecules and classes of formula

1.1.3 Comparison of aliphatic/alicyclic/aromatic compounds - definition & examples

1.1.4 Alkane isomerism explained

1.1.5 Homologous series of alkane examples, general formula CnH2n+2 including isomers of molecular formulae up to C7H16 (up to n = 7)

1.1.6 Examples of cycloalkanes 'alicyclic' compounds of general formula CnH2n

1.1.7 All 18 alkane isomers of C8H18 * 1.1.8 Examples of alkane isomers of C9H20

1.1.9 Examples of alkane isomers of C10H22

and also

Multiple choice Quiz on the structure and naming (nomenclature) of ALKANES

Type in name  Quiz on the structure & naming of ALKANES (and naming cycloalkanes)

Combined multiple choice and type in name quiz on alkanes

Matching pair quiz on hydrocarbon structure

Alkanes and Petrochemical Industry INDEX

All Advanced Organic Chemistry Notes

Index of GCSE/IGCSE Oil - Useful Products Chemistry Revision Notes



1.1.1 A brief guide to the structure and nomenclature of non-cyclic alkane hydrocarbons

The chemical bonding in alkane molecules
  • Most alkanes you will come across are relatively small molecules in which all the chemical bonds are covalent bonds.
  • All the bonds in alkane molecules are single covalent bonds i.e. CC carbon carbon or single CH carbon hydrogen bonds.
  • Each carbon atom forms four single bonds and hydrogen atoms form one single bond.
  • All single covalent bonds are formed by sharing a pair of electrons e.g. one from each of a carbon atom and a hydrogen atom, or two carbon atoms contributing (sharing) an electron each to the covalent bond.
  • These single covalent C-C and C-H bonds are known as sigma bonds (σ).
  • Four (c) doc b hydrogen atoms (1 outer electron) and one  (c) doc b carbon atom (four outer electrons) combine to form methane so that the hydrogen atoms are electronically like helium (full outer shell of 2 electrons) and the carbon atom becomes like neon (with a full outer shell of 8 electrons, the two inner electrons of carbon are not shown).
  • In terms of 'dot and cross' Lewis diagrams the structures of alkanes would be drawn as ...
  • (c) doc b or the alkane methane
  • Similarly six hydrogen atoms combine with two carbon atoms to form the ethane molecule.
  • or the alkane ethane
  • BUT, these do not show the 3D shape of alkane molecules see later.
  • General formula and structural formula of alkanes and alkane nomenclature (naming alkane compounds)
 n of general formula CnH2n+2 1 2 3 4 5 6 7 8 9 10
molecular formula of alkane CnH2n+2 CH4 C2H6 C3H8 C4H10 C5H12 C6H14 C7H16 C8H18 C9H20 C10H22
alkane name (straight chain from C4) methane ethane propane butane pentane hexane heptane octane nonane decane
molecular empirical formula CH4 CH3 C3H8 C2H5 C5H12 C3H7 C7H16 C4H9 C9H20 C5H11
alkyl side chain group prefix name methyl ethyl propyl butyl pentyl hexyl heptyl octyl nonyl decyl
alkyl group formula CnH2n+1 CH3 C2H5 C3H7 C4H9 C5H11 C6H13 C7H15 C8H17 C9H19 C10H21
  • The structural formula can be written as e.g. CH3CH3 (ethane), CH3CH2CH2CH2CH3 or CH3(CH2)3CH3 pentane

    • CH3CH2CH2CH2CH2CH2CH2CH3 or CH3(CH2)6CH3 octane etc.

      • More on molecular representations in 1.1.2., but the style of molecular representation above would be described as an abbreviated or condensed structural formulae. It is an unambiguous representation, as long as you can translate it correctly into e.g. the full displayed formula showing every atom and bond.

      • e.g. for butane CH3CH2CH2CH3 this becomes doc b oil notes

    • The structural formula of the alkyl groups are written in a similar manner to the above minus a H e.g.

    • CH3CH2 ethyl, CH3CH2CH2 propyl, CH3CH2CH2CH2CH2 or CH3(CH2)3CH2 pentyl

  • The primary suffix name is based on the longest carbon chain and ending in ...ane.

    • 1 carbon, methane; 2 carbons, ethane; 3 carbons in chain, propane; 4 carbons in chain, butane.

    • After these four 'historic' preserved 'old trivial' names, the name is 'numerically' systematic according to IUPAC e.g. C5 carbon chain pentane; C6 chain hexane, C7 chain heptane, C8 chain octane, C9 chain nonane, C10 chain decane etc.

      • The IUPAC acronym stands for the International Union of Pure and Applied Chemistry, and one responsibility of this organisation is the development and maintenance of a systematic method of naming compounds that is recognised by chemists from all around the world - an truly international nomenclature.

    • The table above lists the molecular formula and names of the first ten linear alkanes (the term linear applies to butane onwards, i.e. from whence chain isomerism is possible.

  • If all the carbon atoms of the molecule are in one continuous chain, it is referred to as unbranched or linear.

    • e.g. pentane alkanes structure and naming (c) doc bis linear or unbranched.

  • If another chain of carbon atoms starts out of the main carbon chain, it is referred to as branching, giving rise to 'branched' alkane, one with a side-chain.

    • e.g. 3-ethylpentane alkanes structure and naming (c) doc bis branched, because it has an 'ethyl branch' from the 3rd carbon atom in the main chain. Structural formula style.

    • The longest continuous chain of 5 carbon atoms forms the basis of the name - more on this below.

    • alkanes structure and naming (c) doc b Note that you need a minimum of 4 carbon atoms in the alkane molecule to create a side chain branch as in the case of methylpropane.

    • You must always use the longest continuous carbon chain as the basis of the IUPAC systematic name and the lowest possible substituent numbers.

      • For example it would be wrong to name the above molecules triethylmethane or trimethylmethane, and

      • alkanes structure and naming (c) doc bwould not be named 2-propylpropane or 4-methylpentane, but 2-methylpentane,

      • alkanes structure and naming (c) doc bwould not be named 2-ethylbutane or 3-ethylbutane, but 3-methylpentane

    • The 3- denotes the position of the carbon chain branch i.e. the lowest number possible for the start of the side-chain.

  • The positions of the substituent alkyl groups (side chains or 'branches') are denoted by using the lowest possible number(s)

    • e.g. 2, 3 etc. for the associated carbon atoms in the main chain, where the 1st carbon atom in the chain is considered as C atom 1 and can't have an alky substituent, since that merely elongates the longest carbon chain.

  • If there is more than one 'type' of substituent e.g. using the prefixes: methyl..., dimethyl..., trimethyl, ethyl..., diethyl etc., they are written out in alphabetical order (BUT di, tri etc. are ignored in using this rule, so ).

    • 3-ethyl-2,4-dimethylhexane , alkanes structure and naming (c) doc b is good example!

    • Note the use of the lowest number 2 as the basis for working out all the other numbers!

    • This is quoted from near the end of this page, but there are numerous simple examples before that!

  • Some 'old' names are quoted in (italics) though their use should be avoided if possible [but many still used - just put one into GOOGLE!].

  • The alkane names in bold are the preferred IUPAC names.


 

1.1.2 Ways of representing the structure of molecules and classes of formulae

This is illustrated by looking at the structure of the propane, 2-methyl propane and butane molecules. Follow the sequence of bullet points down, and then back up, so you are quite clear on the relationship between all the structural and formula styles.

  • The empirical formula means the simplest possible formula showing the whole number stoichiometric ratio of the different atoms (elements) in the compound.

  • The molecular formula summarises all the atoms in the molecule BUT does not show their arrangement at all.

    • C3H8 is the of molecular formula for propane and C4H10 that of butane and 2-methylpropane.

    • Note that for propane, the empirical formula is identical to the molecular formula BUT for 2-methylpropane and butane, they are not identical. In the case of the latter, the molecular formula is 'twice' the empirical formula.

    • Note also, that the molecular formula, does NOT distinguish the two structural isomers butane and 2-methylpropane ('methylpropane').

      • The 2- is not strictly required, since the branching must occur on the middle carbon as you will see below, where we introduce examples of the more advanced IUPAC naming system that accompanies the unambiguous representation and naming of molecular structures.

  • An abbreviated, condensed or shortened structural formula, is unambiguous if you know how to interpret it!

    • It shows how groups of atoms are linked or sequenced in a molecule but it doesn't always show all the bonds.

    • propane alkanes structure and naming (c) doc b or alkanes structure and naming (c) doc b , abbreviated and more detailed styles of alkane structural formulae.

    • The abbreviated structural formula is the minimum possible unambiguous representation of a molecule AND essential to distinguish different structures of the same molecular formula i.e. structural isomers like methylpropane and butane.

    • methylpropane alkanes structure and naming (c) doc b

    • butane alkanes structure and naming (c) doc b or alkanes structure and naming (c) doc b

    • Note that methylpropane and butane can now be distinguished, BUT, you must be able to envisage these correctly into a full displayed formula structure that shows how all the atoms are 'connected', and this is explained next.

  • A full structural/graphic/displayed formula gives a '2D' projection-representation of the molecule and must clearly show how all the atoms are connected i.e. in this case all the C-C and C-H covalent bonds, but does it not give the full 3D structural, or spatial arrangement, of the atoms, though for most purposes, this level of detail is quite sufficient.

    • propane alkanes structure and naming (c) doc b , unfortunately it does give the impression that the bond angles are 90o, rather than the true angles, many of which are ~109o based on the tetrahedrally arrangement of four single bonds around the carbon atoms in alkane molecules.

     

    • methylbutane

     

    • butane doc b oil notes

     

    • You can use a mixture of styles of the abbreviated structural and displayed formulae.

      • e.g. 2-methylbutane alkanes structure and naming (c) doc b but take care!

       

  • A stereochemical formula is the full displayed formula in terms of the 3D structural or spatial arrangement of the atoms (albeit on a '2D' screen or paper).

    • Only e.g. ball and stick models can fully show the 'true' spatial arrangement of all the atoms, more than adequately simulated by modern computer software for 'molecular modelling'. In the 'picture' of propane below.

    • Imagine the single thin lines as the C-C bonds lying in the plane of the screen/paper, the dotted C-H bonds point away from you, and the triangular wedge C-H bonds point towards you out of the plane of the screen/paper. All the C-C-C, C-C-H or H-C-H bond angles are 109o in this case, and similarly for all other non-cyclic alkanes.

    • propane alkanes structure and naming (c) doc b This kind of representation is essential for displaying e.g. mirror image optical isomers (enantiomers). See Isomerism Part 2a.

    • An important point to appreciate from a 3D representation is that for sigma bonds (single C-C bonds here) there is free rotation of any alkyl group about any C-C bond.

    • Ethane is also represented by a ball-and-stick model molecular diagram AND a space-filling model molecular diagram.

  • alkanes structure and naming (c) doc bis the skeletal formula for propane. Wow, that simple!

    • Skeletal formula (e.g. of alkanes) are very simplified organic formulae shown by removing hydrogen atoms from alkyl chains leaving just lines for the carbon skeleton bonds and associated functional groups (the latter does not apply to alkanes.

      • Skeletal formula should be drawn in such way as to give an impression of the shape of the molecule, at least an idea of the spatial arrangement of the carbon chain - the 'backbone' of the molecule.

    • This is derived by drawing a short line to represent a C-C single bond, so the V shape for propane comes from the C-C-C carbon chain skeleton and the C-C-C bond angle of ~109o.

    • No lines are shown for C-H bonds, they are assumed.

    • However, bond lines should be drawn for C-X bonds, where X is not a hydrogen atom (see e.g. alcohols and ethers).

    • methylpropane is alkanes structure and naming (c) doc b showing the main C-C-C chain and a single carbon branch from the middle carbon.

    • butane is alkanes structure and naming (c) doc b showing the 'linear', but actually zig-zag C-C-C-C chain of 4 with no branching.

    • alkanes structure and naming (c) doc b represents 3-methylhexane. A zig-zag line of 5 C-C bonds (but 6 C atoms) and a dash from the 3rd carbon atom indicating the C-C bond to the methyl group.

    • alkanes structure and naming (c) doc b is 3-ethylpentane, you need an extra alkanes structure and naming (c) doc b to indicate ethyl.

  • See also ball and stick/ball and spring models and space-filling models for ethane.

  • A general formula e.g. CnH2n+2 for non-cyclic alkanes, represents a member of a homologous series when n is designated an integer value for the number of carbon atoms (in the alkane molecule)

    • e.g. if n = 5, it gives the molecular formula of pentane C5H12.

    • A homologous series is a series of compounds with the same functional group in which each member differs from the next member by a constant amount e.g. for alkanes, the addition of a -CH2- 'unit' as the series is ascended n = 1, 2, 3 etc.

    • Consequently, they have a very similar molecular structure, very similar physical and chemical properties.

    • However, within a homologous series, the members will show trends in physical properties like increasing boiling point or decreasing solubility, which are a function of intermolecular forces that increase with chain length.

    • A functional group is a group of atoms responsible for the characteristic reactions of a compound.

    • BUT, alkanes do not have a specific functional group, but they do form a homologous series of compounds with the same sort of molecular structure and similar chemistry, namely chains of carbon atoms combined with the maximum number of hydrogen atoms - so they are saturated hydrocarbon molecules.


 

1.1.3 A simplified structural comparison of aliphatic, alicyclic and aromatic hydrocarbon compounds

  • The names in bold are the preferred IUPAC names.

  • 1. ALIPHATIC - have no benzene ring in their structure (see 3.) and can have an open linear carbon chain, or branched carbon chain structure or a carbon ring structure. If they have a non-benzene ring cyclic structure, they may be termed alicyclic, but they are still aliphatic (see 2.) examples of linear and branched aliphatic alkane compounds.

    • heptane, alkanes structure and naming (c) doc b or alkanes structure and naming (c) doc b   (linear alkane)

    • 2-methylbutane, alkanes structure and naming (c) doc b or alkanes structure and naming (c) doc b  (branched alkane)

    • and lots more examples on this page!

    • Note the general formula for non-cyclic alkanes is CnH2n+2

 

  • 2. ALICYCLIC - these molecules have an aliphatic structure but contain a cyclic or ring structure of at least 3 carbon atoms (can't be less than 3 and must be carbon!) BUT not a benzene ring e.g.

    • Cyclobutane, cyclopentane, cyclohexane

    • alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b    and    alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b    and    alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b, no branches here

    • Methylcyclohexane, alkanes structure and naming (c) doc b or alkanes structure and naming (c) doc b, a branched example of an alicyclic alkane.

    • Alicyclic alkanes resemble the aliphatic molecules illustrated in 1. both physically and chemically, and there are lots more of them on this page!

    • NOTE that later in your course you will meet lots of other homologous series of aliphatic compounds e.g. alkenes, alcohols and halogenoalkanes etc. some of which may have an aliphatic/alicyclic ring structure.

    • Note the general formula for cyclic alkanes (alicyclic) is CnH2n  (two hydrogens less than non-cyclic alkanes)

     

  • 3. AROMATIC - These molecules contain a benzene ring based a 'special' cyclic C6 system, which is an unsaturated ring (BUT not an alkene system) e.g.

    • benzene C6H6, (c) doc b or (c) doc b

     

    • methylbenzene C7H8, C6H5CH3 or (c) doc b or (c) doc b or (c) doc b

    • and lots more on the 'Aromatic molecules' page whether they be aromatic hydrocarbons or phenols etc.

     

  • NOTE:

    • (i) Some molecules can be classified in several ways depending on which part of their structure imparts the functional group chemistry you might be interested in e.g.

      • phenylethene ('styrene'),(c) doc b is named as a derivative of ethene, but its chemistry could be that of an aliphatic alkene (C=C group) or an aromatic compound (contains a benzene ring).

       

    • (ii) Substituted hydrocarbons e.g. a halogen replacing a hydrogen atom on the carbon chain, does not affect these basic definitions e.g.

      • aliphatic: 2-chloropropane, (c) doc b or (c) doc b

       

      • alicyclic: fluorocyclopropane, (c) doc b , (c) doc b

       

      • aromatic: 2,3-dichloromethylbenzene, (c) doc b


 

1.1.4 A brief guide to working out isomers of non-cycloalkanes CnH2n+2

The alkane names in bold are the preferred IUPAC names.

  • Isomers are molecules with the same molecular formula but different in some way in their molecular structure.

  • With alkanes you get structural isomerism because you can vary the arrangement of atoms in the carbon chain.

  • Structural chain isomers of alkanes

  • No structural isomers exist for methane, ethane or propane.

  • However, from C4H10 onwards structural isomers exist. (for other examples and explanation see Isomerism Part 1)

  • C4H10 can be set out as a linear carbon chain to give butane itself.

    • alkanes structure and naming (c) doc b

      • Or you can make a 3 carbon chain with a 'branch in the middle to give methylpropane.

    • alkanes structure and naming (c) doc b and that's it, two isomers for C4H10.

     

  • For C5H12 you can make 3 isomers:

    1. alkanes structure and naming (c) doc b pentane, longest possible linear or 'unbranched chain'.

    2.  alkanes structure and naming (c) doc b, 2-methylbutane, longest chain with a single branch shortening the main chain by 1 carbon.

    3. alkanes structure and naming (c) doc b 2,2-dimethylpropane, shortest possible main chain by double branching and shortening the main chain by 2 carbons.

  • You can extend these ideas from C6H14 onwards, working out by trial and error all the possible branchings in terms of methyl, dimethyl, trimethyl or ethyl groupings etc. I've described lots of alkane examples on this page.

  • The 18 structural chain isomers of C8H18 are worked out for you in section 1.1.7 and anything else from C6-C7 or C9 onwards, you can work out for yourself!

  • Optical (R/S) isomerism occurs from molecular formula C7H16 onwards.

    • R/S isomerism occurs when you have a chiral carbon atom or asymmetric carbon atom in the molecule, that is a carbon atom with 4 different atoms/groups attached to it. It is then possible to have two non-superimposable mirror image forms - two molecular versions with the same molecular formula.

  • The first possible example i.e. with 4 different groups attached to give a chiral carbon is 3-methylhexane.

  • alkanes structure and naming (c) doc b

  • The 4 different groups are -H, -CH3, -CH2-CH3 and -CH2CH2CH3 attached to the central asymmetric/chiral carbon atom.

  • The mirror-image forms (enantiomers) would be extremely difficult to separate.

  • Other examples and explanation of Optical (R/S) Isomerism.


 

1.1.5 The homologous series of alkanes - non-cyclic saturated hydrocarbons with up to 7 carbon atoms for the general formula CnH2n+2 

The alkane names in bold are the preferred IUPAC names.

  1. (a) alkanes structure and naming (c) doc b the molecular formula of methane, two full structural graphic/displayed formula representations are

    • (b)alkanes structure and naming (c) doc b (displayed formula) and (c)alkanes structure and naming (c) doc b which gives a 3-dimensional (3D) structural formula impression of the molecule.

    • The H-C-H bond angle is 109.5o giving a perfect tetrahedral shape so ALL the C-C-H, H-C-H or H-C-H angles are approximately 109o in all the non-cyclic alkanes shown below.

    • is a 3D ball and stick representation of the methane molecule.

    • The tetrahedral shape of methane arises from the mutual repulsion of four bonding pairs of electrons around the central carbon atoms.

      • Although only methane can have a tetrahedral shape, the same electron pair repulsion theory predicts, correctly, that, apart from cyclopropane, cyclobutane and cyclopentane, all the C-C-C, C-C-H and H-C-H bond angles will be approximately 109o in linear alkanes, branched alkanes and cyclic alkane molecules from cyclohexane onwards.

      • For more see dot & cross diagrams and molecule shapes derived from electron pair repulsion theory

     

  2. structural formulae (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b

    1. or displayed formulae (c)alkanes structure and naming (c) doc b or (d)alkanes structure and naming (c) doc b ethane,

    • molecular formula (e)alkanes structure and naming (c) doc b, the skeletal formula is (f)alkanes structure and naming (c) doc b, yes! just a dash!

    • NOTE: from (a) to (d) you go from the most abbreviated structural formula representation to the maximum 3D structural graphic formula representation on a 2D format!

    • The shape is essentially derived from two tetrahedral bond networks linked by the common C-C bond.

    • ball-and-stick model of ethane showing the typical bond angles of approximately 109o for H-C-H and C-C-H bond angles in non-cyclic saturated hydrocarbons i.e. alkanes.

    • space-filling model of ethane

     

  3. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b or

    1. (c)alkanes structure and naming (c) doc b or (d)alkanes structure and naming (c) doc b

    • (a) and (b) are the abbreviated structural formula for propane,

    • (c) and (d) full displayed structural formula, but (d) is a 3D version to indicate the spatial arrangement of the atoms,

    • for molecular formula (e)alkanes structure and naming (c) doc b and the skeletal formula is (f)alkanes structure and naming (c) doc b

    • All the C-C-C, C-C-H or H-C-H bond angles are ~109o. and this applies to all the rest of the linear or branched alkanes which are NOT cyclic.

     

  4. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b are abbreviated structural formula for butane

    •  (normal or n-butane), molecular formula (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  5. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b are the abbreviated structural formula for methylpropane (isobutane), the prefix 2- isn't strictly needed. BUT can be added for clarity, especially for beginners,

    • the molecular formula is (c) alkanes structure and naming (c) doc b and

    • the skeletal formula is (d)alkanes structure and naming (c) doc b and is the simplest branched hydrocarbon.

     

  6. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b are abbreviated structural formula

    •  for pentane (normal or n-pentane), molecular formula (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  7. (a)alkanes structure and naming (c) doc b (b)alkanes structure and naming (c) doc babbreviated structural formula for methylbutane (isopentane),

    • (prefix 2- isn't strictly needed, but 2-methybutane helps at the beginning of studying organic nomenclature), the molecular formula is (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  8. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b are the abbreviated structural formula for dimethylpropane (neopentane),

    • (the prefix 2,2- isn't strictly needed but can help initially),

    • molecular formula (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  9. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b

    • are abbreviated structural formula for hexane (normal or n-hexane),

    • molecular formula (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  10. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b are abbreviated structural formula for

    •  2-methylpentane (NOTE: prefix numbers definitely needed from now on),

    • molecular formula alkanes structure and naming (c) doc band the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  11. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b are abbreviated structural formula

    •  for 3-methylpentane, the molecular formula is (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  12. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b are abbreviated structural formula for

    •  2,2-dimethylbutane (NOTE: numbers needed here, cross-check with 7.),

    • molecular formula (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  13. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b are abbreviated structural formula for

    • 2,3-dimethylbutane, molecular formula (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  14. (a)alkanes structure and naming (c) doc b 

    • or (b)alkanes structure and naming (c) doc b

    • are the abbreviated structural formula for heptane, molecular formula (c)alkanes structure and naming (c) doc b

    • and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  15. (a)alkanes structure and naming (c) doc b 

    • or (b)alkanes structure and naming (c) doc b 

    • are the abbreviated structural formula for 2-methylhexane,

    • molecular formula (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  16. (a)alkanes structure and naming (c) doc b

    • or (b)alkanes structure and naming (c) doc b 

    • are abbreviated structural formula for 3-methylhexane, molecular formula (c)alkanes structure and naming (c) doc b

    • and the skeletal formula is (d)alkanes structure and naming (c) doc b , has an asymmetric carbon atom so will exhibit optical (R/S) isomerism

     

  17. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b are abbreviated structural formula

    • for 3-ethylpentane, molecular formula (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  18. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b are abbreviated structural formula

    • for 2,2-dimethylpentane, molecular formula (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  19. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b  are abbreviated structural formula

    • for 2,3-dimethylpentane, molecular formula (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b  , has an asymmetric carbon atom so will exhibit optical (R/S) isomerism

     

  20. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b  are abbreviated structural formula

    • for 2,4-dimethylpentane, molecular formula (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  21. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b  are abbreviated structural formula

    •  for 3,3-dimethylpentane, molecular formula (c)alkanes structure and naming (c) doc b and the skeletal formula is (d)alkanes structure and naming (c) doc b

     

  22. (a)alkanes structure and naming (c) doc b or (b)alkanes structure and naming (c) doc b are the abbreviated structural formula for

    • 2,2,3-trimethylbutane, molecular formula alkanes structure and naming (c) doc band the skeletal formula is (d)alkanes structure and naming (c) doc b


 

1.1.6 Cycloalkanes (general formula  CnH2n & isomeric with non-cyclic alkenes)

The alkane names in bold are the preferred IUPAC names.

  • Cycloalkanes are named according to the rules previously described, but the name is based on the number of carbon atoms in the ring itself.

  • The 'smallest' cycloalkanes must have at least 3 carbon atoms in the ring.

  • The structures are shown as abbreviated structural formulae and skeletal formulae.

  • They are sometimes referred to as examples of alicyclic hydrocarbons, that is, aliphatic in nature, but with a ring i.e. cyclic-aliphatic compounds, as opposed to an aromatic ring compound based on a benzene ring.

    1. cyclopropane, C3H6 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b note C-C-C bond angle is 60o

    2. because all three carbon atoms are in the same plane, the only cycloalkane in which all the carbon atoms are in the same plane. It means the C-C-C bond is highly strained and easily broken unlike the majority of C-C-C bonds in alkane molecules.

    3. methylcyclopropane, C4H8 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    4. 1,1-dimethylcyclopropane, C5H10 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    5. 1,2-dimethylcyclopropane, C5H10 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    6. ethylcyclopropane, C5H10 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    7. cyclobutane, C4H8 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b note the C-C-C bond angle may look as if it is 90o

    8. but there are two slightly angled 'butterfly' conformations which oscillate from one form to another with maximum C-C-C bond angles of ~88o. In other words the carbon atoms are NOT in the same plane, which is the case for every cycloalkane except cyclopropane (above). The H-C-H bond angles are ~107o in cyclobutane.

    9. methylcyclobutane, C5H10 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    10. 1,1-dimethylcyclobutane, C6H12 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    11. 1,2-dimethylcyclobutane, C6H12 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    12. 1,3-dimethylcyclobutane, C6H12 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    13. ethylcyclobutane, C6H12 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    14. cyclopentane, C5H10 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b, all bond angles ~109o? it is NOT planar, the pentagon is bent.

       

    15. methylcyclopentane, C6H12 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    16. 1,1-dimethylcyclopentane, C7H14 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    17. 1,2-dimethylcyclopentane, C7H14 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    18. 1,3-dimethylcyclopentane, C7H14 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    19. ethylcyclopentane, C7H14 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    20. propylcyclopentane, C8H16 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    21. butylcyclopentane, C9H18 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    22. pentylcyclopentane, C10H20 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    23. cyclohexane, C6H12 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b, all bond angles ~109o NOT 120o, the hexagon is bent into its most stable double pointed chair form - its most stable conformation.

      ball-and-stick diagram of cyclohexane

       

    24. methylcyclohexane, C7H14 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    25. 1,1-dimethylcyclohexane, C8H16 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    26. 1,2-dimethylcyclohexane, C8H16 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    27. 1,3-dimethylcyclohexane, C8H16 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    28. 1,4-dimethylcyclohexane, C8H16 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    29. ethylcyclohexane, C8H16 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    30. propylcyclohexane, C9H18 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    31. butylcyclohexane, C10H20 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

       

    32. pentylcyclohexane, C11H22 , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

 


1.1.7 to 1.1.9 Larger Alkanes with 8-10 carbon atoms CnH2n+2 continued


1.1.7 Illustrated as brief guide to working out the 18 isomers of non-cycloalkanes C8H18

The alkane names in bold are the preferred IUPAC names.

(1) octane, CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH3   

Start with the linear (unbranched) carbon chain, then make the next longest chain with a single, but shortest, carbon branch (-CH3), to give three methylheptanes ...

(2) 2-methylheptane, (CH3)2CHCH2CH2CH2CH2CH3

 

(3) 3-methylheptane, CH3CH2CH(CH3)CH2CH2CH2CH3

 

(4) 4-methylheptane, CH3CH2CH2CH(CH3)CH2CH2CH3

then do double methyl branching permutations to make 6 dimethylhexanes ...

 

(5) 2,2-dimethylhexane,  alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

 

(6) 2,3-dimethylhexane,  alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

 

(7) 2,4-dimethylhexane,  alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

 

(8) 2,5-dimethylhexane,  alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

 

(9) 3,3-dimethylhexane, alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

 

(10) 3,4-dimethylhexane,  alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

then you can make one ethylhexane ...

 

(11) 3-ethylhexane,  alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

and don't try 2-ethylhexane, because its actually 3-methylheptane using the nomenclature rules correctly.

Now you can do a double branching again to make two ethylmethylpentanes ...

 

(12) 3-ethyl-2-methylpentane, alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

 

(13) 3-ethyl-3-methylpentane,  alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

and you can do a triple branching to give four trimethylpentanes ...

 

(14) 2,2,3-trimethylpentane, (CH3)3CCH(CH3)CH2CH3

(15) 2,2,4-trimethylpentane (isooctane), (CH3)3CCH2CH(CH3)2, ,

 

(16) 2,3,3-trimethylpentane, (CH3)2CHC(CH3)2CH2CH3

 

(17) 2,3,4-trimethylpentane, (CH3)2CHCH(CH3)CH(CH3)2

Then finally, the most branched isomer is the single tetramethylbutane (shortest possible main chain) ...

 

(18) 2,2,3,3-tetramethylbutane, (CH3)3CC(CH3)3

 


1.1.8 Examples of isomers of C9H20

The alkane names in bold are the preferred IUPAC names.

  • 3-ethyl-2,2-dimethylpentane, alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

     

  • 3-ethyl-2,3-dimethylpentane, alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

     

  • 3-ethyl-2,4-dimethylpentane, alkanes structure and naming (c) doc b,alkanes structure and naming (c) doc b

     

  • 3-ethyl-2-methylhexane , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

     

  • 3-ethyl-3-methylhexane , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

     

  • 3-ethyl-4-methylhexane , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

     

  • 4-ethyl-2-methylhexane , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

     


1.1.9 Examples of isomers of C10H22  (many have an asymmetric carbon atom so will exhibit optical (R/S) isomerism)

The alkane names in bold are the preferred IUPAC names.

  • 3-ethyl-2,2-dimethylhexane , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

     

  • 3-ethyl-2,3-dimethylhexane , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

     

  • 3-ethyl-2,5-dimethylhexane , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

 

  • 3-ethyl-2,4-dimethylhexane , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

     

  • 4-ethyl-2,2-dimethylhexane , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

     

  • 4-ethyl-2,3-dimethylhexane , alkanes structure and naming (c) doc b, alkanes structure and naming (c) doc b

     

  • 4-ethyl-3,3-dimethylhexane , alkanes structure and naming (c) doc b


A Level Organic Chemistry Part 1 sub-index:

1.1.1 Alkane nomenclature explained

1.1.2 Different ways of representing molecules and classes of formula

1.1.3 Comparison of aliphatic/alicyclic/aromatic compounds - definition & examples

1.1.4 Alkane isomerism explained

1.1.5 Homologous series of alkane examples, general formula CnH2n+2 including isomers of molecular formulae up to C7H16 (up to n = 7)

1.1.6 Examples of cycloalkanes 'alicyclic' compounds of general formula CnH2n

1.1.7 All 18 alkane isomers of C8H18 * 1.1.8 Examples of alkane isomers of C9H20

1.1.9 Examples of alkane isomers of C10H22

and also

Multiple choice Quiz on the structure and naming (nomenclature) of ALKANES

Type in name  Quiz on the structure & naming of ALKANES (and naming cycloalkanes)

Combined multiple choice and type in name quiz on alkanes

Matching pair quiz on hydrocarbon structure

Alkanes and Petrochemical Industry INDEX

 All Advanced Organic Chemistry Notes

 Index of GCSE/IGCSE Oil - Useful Products Chemistry Revision Notes


formula keywords: how to name naming nomenclature empirical molecular formula graphic formula displayed formula skeletal formula structural isomers isomerism  CH4 C2H6 CH3CH3 CH3-CH3 C3H8 CH3CH2CH3 CH3-CH2-CH2-CH3 C4H10 CH3CH2CH2CH3 CH3-CH2-CH2-CH3 C4H8 C5H12 C5H10 C6H14 C6H12 C7H16 C8H18 C9H20 C10H22 chemistry revision notes structure of alkanes AS AQA GCE A level chemistry how do you name alkanes? AS Edexcel GCE A level chemistry alkane nomenclature rules AS OCR GCE A level chemistry what is the molecular structure of alkanes? AS Salters GCE A level chemistry how to work out isomers of alkanes US grades 11 & 12 chemistry IUPAC naming of alkanes notes for revising the structure and naming of linear and cyclic alkanes how to name alkanes for AQA AS chemistry, how to name alkanes for Edexcel A level AS chemistry, how to name alkanes for A level OCR AS chemistry A, how to name alkanes for OCR Salters AS chemistry B, how to name alkanes for AQA A level chemistry, how to name alkanes for A level Edexcel A level chemistry, how to name alkanes for OCR A level chemistry A, how to name alkanes for A level OCR Salters A level chemistry B how to name alkanes for US Honours grade 11 grade 12 how to name alkanes for pre-university chemistry courses pre-university A level revision notes for how to name alkanes  A level guide notes on how to name alkanes for schools colleges academies science course tutors images pictures diagrams for how to name alkanes A level chemistry revision notes on how to name alkanes for revising module topics notes to help on understanding of how to name alkanes university courses in science careers in science jobs in the industry laboratory assistant apprenticeships technical internships USA US grade 11 grade 11 AQA A level chemistry notes on how to name alkanes Edexcel A level chemistry notes on how to name alkanes for OCR A level chemistry notes WJEC A level chemistry notes on how to name alkanes CCEA/CEA A level chemistry notes on how to name alkanes These detailed notes on the structure and naming of alkanes include the general formula of alkane molecules, empirical formula of alkane molecules, structural formula of alkane molecules, skeletal formula of alkane molecules, displayed formula of alkane molecules, shapes of alkane molecules, isomers of alkane molecules IUPAC rules for alkane nomenclature. Students should be able to draw structural formula of alkane, displayed and skeletal formulas for alkane organic compounds apply IUPAC rules for nomenclature to name alkane acid organic compounds including chains and rings and be able to apply IUPAC rules for nomenclature to draw the structural, displayed or skeletal structure of alkane organic compounds from the alkane IUPAC name from the homologous series of alkanes

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