Part 5. Carbonyl chemistry of ALDEHYDES & KETONES

5. The structure and nomenclature - naming of Aldehydes & Ketones

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK KS5 A/AS GCE IB advanced level organic chemistry students US K12 grade 11 grade 12 organic chemistry

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Revision Notes Part 5 CARBONYL COMPOUNDS - NOMENCLATURE of ALDEHYDES and KETONES

5.1 The molecular structure and naming of ALDEHYDES and KETONES - including nomenclature of some isomers

Nomenclature of aldehydes & ketones names and structures of aldehydes & ketones How to name aldehydes? How to name ketones? Nomenclature of substituted aldehydes or ketones - examples of acceptable names, displayed formula of aldehydes and ketones, graphic formula of aldehydes and ketones, molecular formula of aldehydes and ketones, skeletal formula of aldehydes and ketones, structural formula of aldehydes and ketones and homologous series of aldehydes and ketones, how to name the carbonyl group of compounds known as aldehydes and ketones

Part 5.1 sub-index for naming and structure of aldehydes and ketone

5.1.1 Nomenclature introduction to naming aliphatic aldehydes and ketones

5.1.2 Examples of aldehydes

5.1.3 Examples of ketones

5.1.4 Other examples of substituted ketones

5.1.5 Aromatic aldehydes and ketones

5.1.5 Oxidation sequence: alcohol ==> aldehyde/ketone ==> carboxylic acid

5.1.1 Introduction to Aldehyde and Ketone Nomenclature

• How do you name aldehydes? How do you name ketones? How do you name substituted aldehydes or substituted ketones?
• Aldehydes and ketones are a group of compounds containing the carbonyl group, C=O.
• Aldehydes always have a hydrogen atom attached to the carbon of the carbonyl group, so their functional group is -CHO (see diagram above).
  • The functional group is shown by using 'al' in the suffix part of the name e.g. methanal, ethanal, propanal etc.
  • The prefix for the aldehyde name is based on the parent alkane minus the e.
  • No number is required for the aldehyde group because the aldehyde group cannot be anything else except carbon atom 1.
    • A number would only be required if a higher ranking group is present e.g. a -COOH carboxylic acid group.
    • Aliphatic aldehydes have the general formula C_n-1H_2n-1CHO, n = 1, 2, 3 etc.
    • This generates using simplified/abbreviated structural formulae for aliphatic aldehydes ...
      •  methanal HCHO,  ethanal CH₃CHO,  propanal CH₃CH₂CHO,  butanal CH₃CH₂CH₂CHO
      • then pentanal CH₃CH₂CH₂CH₂CHO,  hexanal CH₃CH₂CH₂CH₂CH₂CHO or CH₃(CH₂)₄CHO etc.
    • The first four names of aldehydes are derived from the accepted trivial historic names of the parent alkane and then IUPAC rules dictate that you then use the numerically derived names from pentan, hexan, heptan, octan etc..
    • The usual minimum numbering system is used to give the preferred IUPAC name e.g. for a side-chain alkyl group substituent like in ...
      • 3-methylbutanal ,
      (structural formula and skeletal formula)
      • You sometimes see the H of the aldehyde group shown on the skeletal formula, but I'm not sure whether this is acceptable in exams?, I've tended to be quite strict with my skeletal formula representations of aldehydes.
      • The aldehyde group is carbon atom 1 and the substituent methyl group is attached to carbon atom 3 in the longest possible carbon chain.
      • If asked for a structural formula, do NOT use the very abbreviated style, use the above or a fully displayed formula style like for the aldehyde ethanal.
  • Because there is only one oxygen in the molecular formula, the empirical formula of aldehydes (and ketones) is always the same as molecular formula - you can't halve an oxygen atom!
• Ketones always have two carbon atom groups attached to the carbon atom of the carbonyl group, so the functional group is written as C-CO-C (remember CO in abbreviated structural formulae of ketones is actually >C=O).
  • The prefix for the ketone name is based on the parent alkane minus the e.
  • The functional group is shown by using 'one' in the suffix part of the name e.g. propanone, butanone, hexan-3-one etc.
  • A number to denote the position of the ketone group is definitely required beyond butanone and although not strictly needed for butan-2-one, since only one ketone position is possible, it is required for substituted butanones and beyond.
  • A ketone must have a minimum of three carbon atoms to get two alkyl groups attached to the carbon atom of the carbonyl group.
  • For the same 'carbon number', aldehydes and ketones are structural and functional group isomers based on e.g. for aliphatic carbonyl compounds C_nH_2nO.
    • So, ketones are functional group structural isomers of aldehydes for the same molecular formula e.g.
    • butanal and butanone
  • Using abbreviated structural formulae, where CO is actually >C=O, you get ..
  • propanone CH₃COCH₃,  butanone CH₃COCH₂CH₃, where no functional group positional number is needed, but after this from C₅ ketones onwards, a positional number is needed to correctly derive the IUPAC name for ketones ...
  • so we have .. pentan-2-one CH₃COCH₂CH₂CH₃ which is isomeric with pentan-3-one CH₃CH₂COCH₂CH₃
  • and hexan-2-one CH₃COCH₂CH₂CH₂CH₃ which is isomeric with hexan-3-one CH₃CH₂COCH₂CH₂CH₃  etc.
    • There are two pentanones and hexanones, but you should be able to recognise that there are three linear heptanones!
    • and remember, very abbreviated structural formulae might not be good enough if the structure is requested in an exam question, so use either a 'fuller' structural formula like , or full displayed formula like e.g. for the ketone butanone.
  • The substituent numbers are based on giving the carbonyl C=O carbon of the ketone having the lowest number e.g. 5-iodopentan-2-one (...one group is 2 NOT 4, iodo group is 5- NOT 1- or -4)
    • In other words the C=O functional group is given precedence over substituent groups like alkyl or halogen.
  • The number position of the C=O group in ketones needs to be specified for carbon chains of over 4, or less, if substituents are present e.g. 3-methylbutan-2-one, heptan-2-one, heptan-3-one and heptan-4-one (there is no heptan-1-one, this is heptanal !).
• Some 'old' names are quoted in (italics) though their use should be avoided if possible [but many still widely used in the chemical industry - just put one into GOOGLE!].

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These examples start with the aldehyde's molecular formula, then one or more abbreviated structural formula, then. in some cases, the full displayed formula (full structural formula) and finally the skeletal formula of the aldehyde.

The names in bold are the preferred IUPAC aldehyde name.

1. methanal (formaldehyde), CH₂O, , ,

, the simplest and first in the series of aliphatic aldehydes

Methanal is a trigonal planar shape and the planarity gives H-C=O and H-C-H bond angles of ~120^o.

2. ethanal (acetaldehyde), C₂H₄O, , , ,

, the 2nd in the aeries

Bond angles from left to right:

• For the 'methyl' group: H-C-C 109^o, H-C-H 109^o

• For the aldehyde group: C-C=O 120^o, C-C-H 120^o and O=C-H 120^o.

• The bond angles around the aldehyde group are 120^o (a planar arrangement) and if the aldehyde molecule does not have a benzene ring, all the rest of the 'alkyl' structure have bond angles ~109^o.

• e.g. the bond angles for C-C-C in the chain, H-C-C, C-C-H or H-C-H (see propanal etc. below).

3. propanal (propionaldehyde),  C₃H₆O, , , ,

• It is common skeletal formula to show the hydrogen atom of the aldehyde group, but I have chosen not to do so, my skeletal formulae obey the rules very strictly.

4. 2-methylpropanal (2 not strictly needed but advisable, 2-methypropionaldehyde),

   • C₄H₈O, , ,

5. butanal (butyraldehyde),C₄H₈O,  , ,

 

6. 2-methylbutanal (2-methylbutyraldehyde), C₅H₁₀O,  ,

7. 3-methylbutanal (3-methylbutyraldehyde) , C₅H₁₀O,  ,

8. pentanal (old name 'valeraldehyde'), C₅H₁₀O,  ,

9. hexanal, C₅H₁₀O, CH₃CH₂CH₂CH₂CH₂CHO

10. C₆H₅CHO, benzaldehyde (benzenecarbaldehyde), and 2-hydroxybenzaldehyde

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These examples start with the ketone's molecular formula, then one or more abbreviated structural formula, then, in some cases, the full displayed formula (full structural formula) and finally the skeletal formula of the ketone.

The names in bold are the preferred IUPAC ketone name.

1. propanone (acetone, dimethyl ketone, DMK), C₃H₆O,  , , ,

Bond angles: The trigonal planarity around the carbonyl group >C=O gives a C-C=O and C-C(=O)-C of 120^o and associated with the methyl group, the H-C-C and H-C-H bond angles are 109^o.

The bond angles around the ketone group are 120^o (a planar arrangement) and if the ketone molecule does not have a benzene ring, all the rest of the 'alkyl' structure have bond angles ~109^o. e.g. C-C-C, C-C-H or H-C-H.

The ketone propanone is isomeric with the aldehyde propanal (functional group structural isomers).

2. butanone (or butan-2-one, but 2 not strictly needed, methyl ethyl ketone, MEK, 2-butanone),

• C₄H₈O,  , , ,

• Bond angles: H-C-C, H-C-H and C-C-C on right are all 109^o and C-C=O on left, C-C(=O)-C and O=C-C on right are 120^o and the angles associated with the methyl group on the right are all 109^o.

• The ketone butanone is isomeric with the aldehyde butanal (functional group structural isomers).

3. 3-methylbutan-2-one

• The molecular formula, structural formula and skeletal formula of this ketone are ....

• C₅H₁₀O,  ,

 , more structural isomers of C₅H₁₀ are shown below  (4. and 5.)

• A similar naming situation arises with , C₄H₈O₂, CH₃COCH(OH)CH₃, 3-hydroxybutanone will do, or 3-hydroxybutan-2-one, which has the trivial name of 'acetoin'.

4. pentan-2-one (2-pentanone), C₅H₁₀O,   , ,

5. pentan-3-one (3-pentanone), C₅H₁₀O,   , ,

6. 3-methylpentan-2-one, C₆H₁₂O,  CH₃COCH(CH₃)CH₂CH₃

7. 4-methylpentan-2-one, C₆H₁₂O,  CH₃COCH₂CH(CH₃)₂

8. hexan-2-one (2-hexanone), C₆H₁₂O,  CH₃COCH₂CH₂CH₂CH₃

9. hexan-3-one (3-hexanone), C₆H₁₂O,  CH₃CH₂COCH₂CH₂CH₃

10. 1-phenylethanone, C₆H₅COCH₃, or just phenylethanone and considered the simplest aromatic ketone.

11. 2-hydroxyphenylethanone (you might consider ketones 10 and 11 as half aliphatic and half aromatic!

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5.1.4 Other examples of substituted ketones e.g. iodoketones and phenylketones

The names in bold are the preferred IUPAC ketone name.

1 to 3, 5 to 6 and 10 are formed by the reaction of the parent ketone with iodine in the presence of an acid (e.g. HCl_(aq), because H⁺_(aq) catalyses the reaction)

1. iodopropanone (1-iodopropanone, 1- not really needed)

2. 1-iodobutan-2-one (1-iodo-2-butanone)

3. 3-iodobutan-2-one (3-iodo-2-butanone)

4. 4-iodobutan-2-one (4-iodo-2-butanone)

5. 1-iodopentan-2-one

6. 3-iodopentan-2-one

7. 4-iodopentan-2-one

8. 5-iodopentan-2-one

9. 1-iodopentan-3-one

10. 2-iodopentan-3-one (2-iodo-3-pentanone)

11. Phenylketones e.g.

    • C₆H₅CH₃COCH₂CH₃  is 1-phenylbutan-2-one (1-phenyl-2-butanone)

    • CH₃COCH(C₆H₅)CH₃  is 3-phenylbutan-2-one (3-phenyl-2-butanone)

    • CH₃COCH₂CH₂C₆H₅  is 4-phenylbutan-2-one (4-phenyl-2-butanone)

    • These are still classed as aliphatic ketones.

12. -

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True aromatic aldehydes, R-CHO, have the aldehyde group -CHO directly attached to the ring e.g.

C₇H₆O, orbenzaldehyde, and

 C₇H₆O₂, 2-hydroxybenzaldehyde

Ketones, R₂C=O, are often 'mixed' aliphatic-aromatic in the sense that one R group is alkyl and the other is aryl e.g.

1-phenylethanone (acetophenone, methyl phenyl ketone), C₈H₈O,  , and C₈H₈O₂,  

Diphenylmethanone (diphenyl ketone), C₁₃H₁₀O, , is a completely aromatic ketone.

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Alcohols can be readily oxidised to aldehydes and ketones and aldehydes are easily oxidised further to carboxylic acids.

The reagent can be potassium dichromate(VI) K₂Cr₂O₇ , acidified with diluted sulphuric acid H₂SO_4(aq) (colour change is orange to green).

For details see 5.3 Methods of preparing aldehydes and ketones

However the oxidation products depend on the original structure of the alcohol. The alcohol functional group -OH in aliphatic alcohols is classified into primary, secondary and tertiary types (see below). When the -OH is attached directly to a benzene ring the molecule is called a phenol.

Primary aliphatic alcohols R-OH, R is H or alkyl: When oxidised they form aldehydes and then further oxidation gives a relatively stable carboxylic acid e.g.

1. ====> ====>

   • ethanol ====> ethanal ====> ethanoic acid

2. ====> ====>

   • 2-methylpropan-1-ol ====> 2-methylpropanal ====> 2-methylpropanoic acid

3.  ====> ====>

   • butan-1-ol ==> butanal ==> butanoic acid

4. ====> ====>

   • pentan-1-ol ====> pentanal ====> pentanoic acid

Secondary aliphatic alcohols R-CH(OH)-R', R or R' are both alkyl (can be aryl): When oxidised they form relatively stable ketones (see NOTE below) e.g.

1.  ====>  , propan-2-ol ====> propanone

2.  ====>  , butan-2-ol ====> butanone (butan-2-one)

3.  ====>  , pentan-3-ol ====> pentan-3-one

Tertiary aliphatic alcohols RR'R"C-OH, where R,R' or R" are all alkyl (or aryl): These are relatively stable to oxidation (see NOTE 1. further down) e.g.

1. 2-methylpropan-2-ol , or

2. 2-methylbutan-2-o l, or

3. 3-methylpentan-3-o l, or

1. Ketones and carboxylic acids are relatively stable to further oxidation because a strong C-C bond must be broken in the process. Prolonged oxidation with H₂SO_4(aq)/K₂Cr₂O₇ or using a more powerful oxidising agent, results in the formation of carbon dioxide, water and carboxylic acids of shorter carbon chain length than the original alcohol or ketone.

2. When a primary alcohol is oxidised to an aldehyde, the oxidation to the carboxylic acid is rapid. If the aldehyde formed first is the desired product, it must be immediately distilled off to prevent further oxidation.  See Organic Oxidations

LINKS TO ASSOCIATED ADVANCED ORGANIC CHEMISTRY PAGES

Multiple choice quiz on naming aldehydes or ketones

Type in name (short answer) quiz on aldehydes and ketones

10.6.1 Carbonyl compounds - ALDEHYDES and KETONES - introduction to their reactions

10.6.2 Nucleophilic addition of hydrogen cyanide to aldehydes & ketones to form a hydroxy-nitrile

10.6.3 Addition of hydrogen to aldehydes and ketones - reduction with LiAlH₄ or NaBH₄ to give alcohols

10.6.4 Iodination of ketones e.g. a 2-one like propanone (a methyl ketone) to give iodo-ketones

Quiz on Organic Structure Recognition

Summary of organic chemistry functional group tests

Intermolecular forces & boiling points of aldehydes & ketones compared to other organic molecules

The shapes and bond angles of simple organic molecules

formula keywords: how to name naming nomenclature empirical molecular formula graphic formula displayed formula skeletal formula structural isomers isomerism 5.1.1 carbonyl compounds Nomenclature introduction * 5.1.2 Examples of aldehydes * 5.1.3 Examples of ketones * 5.1.4 Other examples of substituted ketones  CH2O HCHO C2H4O CH3CHO CH3-CHO C3H6O CH3CH2CHO CH3-CH2-CHO CH3COCH3 CH3-CO-CH3 C4H8O CH3CH2CH2CHO CH3-CH2-CH2-CHO CH3COCH2CH3 CH3-CO-CH2-CH3 C5H10O CH3CH2CH2CH2CHO CH3COCH2CH2CH3 CH3CH2COCH2CH3 C7H6O C6H5CHO C6H5COCH3 chemistry revision notes structure of aldehydes & ketones how to name aldehydes ketone for AQA AS chemistry, how to name aldehydes ketone for Edexcel A level AS chemistry, how to name aldehydes ketone for A level OCR AS chemistry A, how to name aldehydes ketone for OCR Salters AS chemistry B, how to name aldehydes ketone for AQA A level chemistry, how to name aldehydes ketone for A level Edexcel A level chemistry, how to name aldehydes ketone for OCR A level chemistry A, how to name aldehydes ketone for A level OCR Salters A level chemistry B how to name aldehydes ketone for US Honours grade 11 grade 12 how to name aldehydes ketone for pre-university chemistry courses pre-university A level revision notes for how to name aldehydes ketone  A level guide notes on how to name aldehydes ketone for schools colleges academies science course tutors images pictures diagrams for how to name aldehydes ketone A level chemistry revision notes on how to name aldehydes ketone for revising module topics notes to help on understanding of how to name aldehydes ketone 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 aldehydes ketone Edexcel A level chemistry notes on how to name aldehydes ketone for OCR A level chemistry notes WJEC A level chemistry notes on how to name aldehydes ketone CCEA/CEA A level chemistry notes on how to name aldehydes ketone for university entrance examinations describe the molecular structure of aldehydes & ketones, notes on how to name aldehydes & ketones, how to draw skeletal formula of aldehydes & ketones, how to use the IUPAC nomenclature of aldehydes & ketones, examples of aldehydes & ketones molecular structures, diagrams of isomeric aldehydes & ketones, naming isomers of aldehydes & ketones These detailed notes on the structure and naming of aldehydes include the general formula of aldehyde molecules, empirical formula of aldehyde molecules, structural formula of aldehyde molecules, skeletal formula of aldehyde molecules, displayed formula of aldehyde molecules, shapes of aldehyde molecules, isomers of aldehyde molecules These detailed notes on the structure and naming of ketones include the general formula of ketone molecules, empirical formula of ketone molecules, structural formula of ketone molecules, skeletal formula of ketone molecules, displayed formula of ketone molecules, shapes of ketone molecules, isomers of ketone molecules IUPAC rules for aldehyde nomenclature. Students should be able to draw structural formula of aldehyde, displayed and skeletal formulas for aldehyde organic compounds apply IUPAC rules for nomenclature to name aldehyde 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 aldehyde organic compounds from the aldehyde IUPAC name from the homologous series of aldehydes IUPAC rules for ketone nomenclature. Students should be able to draw structural formula of ketone, displayed and skeletal formulas for ketone organic compounds apply IUPAC rules for nomenclature to name ketone 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 ketone organic compounds from the ketone IUPAC name from the homologous series of ketones

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