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aldehydes and ketones nomenclature (c) doc baldehydes and ketones nomenclature (c) doc bDoc Brown's GCE A Level AS A2 Chemistry  Revising Advanced Level Organic Chemistry

Revision Notes Part 5 CARBONYL COMPOUNDS - 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, molecular formula, skeletal formula, structural formula of these homologous series and how to name the carbonyl group of compounds known as aldehydes and ketones

Organic Chemistry Part 5 sub-index: 5.1.1 Nomenclature introduction * 5.1.2 Examples of aldehydes * 5.1.3 Examples of ketones * 5.1.4 Other examples of substituted ketones * 5.1.5 Oxidation sequence: alcohol ==> aldehyde/ketone ==> carboxylic acid * Other advanced level organic chemistry links


Revision notes on the structure and naming-nomenclature of Aldehydes and Ketones

5.1.1 Introduction to Aldehyde and Ketone Nomenclature

aldehydes and ketones nomenclature (c) doc b

  • How do you name aldehydes? How do you name ketones? How do you name substituted aldehydes or 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 the 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.
  • Ketones always have two carbon atoms attached to the carbon atom of the carbonyl group, so the functional group is C-CO-C (see diagram above).
    • 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.
    • The substituent numbers are based on giving the carbonyl C=O carbon the lowest number e.g. 2-methylbutanal ('al' position = 1). The number position of the C=O group in ketones needs to be specified for carbon chains of over 4, or less, if substituents 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!).
  • For the same 'carbon number', aldehydes and ketones are structural and functional group isomers based on e.g. for aliphatic carbonyl compounds CnH2nO.
  • Some 'old' names are quoted in (italics) though their use should be avoided if possible [but many still used - just put one into GOGGLE!].


5.1.2 Examples of Aldehydes

  1. methanal (formaldehyde), aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b

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

  3. ethanal (acetaldehyde), aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b

  4. Bond angles from left to right: H-C-C 109o, C-C=O 120o, C-C-H 120o and O=C-H 120o.

  5. propanal (propionaldehyde), aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b

  6. 2-methylpropanal (2 not strictly needed but advisable, 2-methypropionaldehyde),

    • aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b

  7. butanal (butyraldehyde), aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b

  8. 2-methylbutanal (2-methylbutyraldehyde), aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b

  9. 3-methylbutanal (3-methylbutyraldehyde), aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b

  10. pentanal (old name 'valeraldehyde'),aldehydes and ketones nomenclature (c) doc b , aldehydes and ketones nomenclature (c) doc b

  11. aldehydes and ketones nomenclature (c) doc b benzaldehyde (benzenecarbaldehyde), and aldehydes and ketones nomenclature (c) doc b 2-hydroxybenzaldehyde


5.1.3 Examples of ketones

  1. propanone (acetone, dimethyl ketone, DMK), aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b

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

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

    • aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b

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

  4. 3-methylbutan-2-one (2 and 3 not strictly needed BUT advisable, 3-methyl-2-butanone),

    • aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b

  5. pentan-2-one (2-pentanone), aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b

  6. pentan-3-one (3-pentanone), aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b, aldehydes and ketones nomenclature (c) doc b

  7. 1-phenylethanone aldehydes and ketones nomenclature (c) doc b

  8. aldehydes and ketones nomenclature (c) doc b2-hydroxyphenylethanone


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

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. (c) doc b iodopropanone (1-iodopropanone, 1- not really needed)

  2. (c) doc b1-iodobutanone (1-iodobutan-2-one, -2- not really needed, 1-iodo-2-butanone)

  3. (c) doc b3-iodobutanone (3-iodobutan-2-one, -2- not really needed, 3-iodo-2-butanone)

  4. (c) doc b4-iodobutanone (4-iodobutan-2-one, -2- not really needed, 4-iodo-2-butanone)

  5. (c) doc b1-iodopentan-2-one (-2- needed, 1-iodo-2-pentanone)

  6. (c) doc b3-iodopentan-2-one (-2- needed, 3-iodo-2-pentanone)

  7. (c) doc b4-iodopentan-2-one (-2- needed, 4-iodo-2-pentanone)

  8. (c) doc b5-iodopentan-2-one (-2- needed, 5-iodo-2-pentanone)

  9. (c) doc b1-iodopentan-3-one  (-3- needed, 1-iodo-3-pentanone)

  10. (c) doc b2-iodopentan-3-one (-3- needed, 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)

  12. -


5.1.5 Alcohol oxidation sequences

Alcohols can be readily oxidised to aldehydes and ketones and aldehydes are easily oxidised further to carboxylic acids. The reagent can potassium dichromate(VI) K2Cr2O7 , acidified with diluted sulphuric acid H2SO4(aq) (colour change is orange to green).

For details of the practical method see Organic Redox Reactions

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. aldehydes and ketones nomenclature (c) doc b==>aldehydes and ketones nomenclature (c) doc b==>aldehydes and ketones nomenclature (c) doc b

    • ethanol ==> ethanal ==> ethanoic acid

  2. aldehydes and ketones nomenclature (c) doc b==>aldehydes and ketones nomenclature (c) doc b==>(c) doc b

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

  3. aldehydes and ketones nomenclature (c) doc b ==> aldehydes and ketones nomenclature (c) doc b==>aldehydes and ketones nomenclature (c) doc b

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

  4. aldehydes and ketones nomenclature (c) doc b==>aldehydes and ketones nomenclature (c) doc b==>aldehydes and ketones nomenclature (c) doc b

    • 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. aldehydes and ketones nomenclature (c) doc b ==> aldehydes and ketones nomenclature (c) doc b, propan-2-ol ==> propanone

  2. aldehydes and ketones nomenclature (c) doc b ==> aldehydes and ketones nomenclature (c) doc b, butan-2-ol ==> butanone (butan-2-one)

  3. aldehydes and ketones nomenclature (c) doc b ==> aldehydes and ketones nomenclature (c) doc b, 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 , aldehydes and ketones nomenclature (c) doc b or aldehydes and ketones nomenclature (c) doc b

  2. 2-methylbutan-2-o l, aldehydes and ketones nomenclature (c) doc b or aldehydes and ketones nomenclature (c) doc b

  3. 3-methylpentan-3-o l, aldehydes and ketones nomenclature (c) doc b or aldehydes and ketones nomenclature (c) doc b

NOTE:

  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 H2SO4(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.


LINKS TO ASSOCIATED ADVANCED ORGANIC CHEMISTRY PAGES

Multiple choice quiz on naming aldehydes or ketones

(c) doc bType in name (short answer) quiz on aldehydes and ketones

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

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

All Advanced Organic Chemistry Notes

Summary of Organic Functional Groups Notes

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


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