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Chem 1152: Ch. 14

Chem 1152: Ch. 14. Aldehydes and Ketones. Introduction. Aldehyde: Carbonyl group with one or two H attached. Named by replacing –e with –al (IUPAC). The aldehyde C is always numbered as 1. Ketone: Carbonyl group with two C attached. Named by replacing –e with –one (IUPAC ).

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Chem 1152: Ch. 14

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  1. Chem 1152: Ch. 14 Aldehydes and Ketones

  2. Introduction Aldehyde: Carbonyl group with one or two H attached. • Named by replacing –e with –al (IUPAC). • The aldehyde C is always numbered as 1. Ketone: Carbonyl group with two C attached. • Named by replacing –e with –one(IUPAC). • Numbered from end closest to carbonyl group Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  3. Common Aldehydes and Ketones Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  4. Naming Aldehydes pentanal 5-chloropentanal 2-ethylbutanal m-chloro-benzaldehyde 5-chloro-2-methylbenzaldehyde 3,4-dimethylhexanal 5-methoxy-2-methylbenzaldehyde

  5. Drawing Aldehydes 2-bromo-2-methylpropanal 3-chloropentanal 3-bromo-4-phenylbutanal 2-hydroxy-5-methoxybenzaldehyde

  6. Naming Ketones 1-chloro-3-pentanone 2-pentanone 5-chloro-2-pentanone 4-ethylcyclohexanone 2-fluoro-5-methyl-4-octanone Ketone: Carbonyl group with two C attached. • Named by replacing –e with –one(IUPAC). • Numbered from end closest to carbonyl group

  7. Physical Properties • Carbonyl O cannot form H-bonds between molecules, but can form weaker dipolar bonds. • Carbonyl O can form H-bonds with water (polar solvent) for low MW ketones and aldehydes. • BP values lower than similar alcohols, but higher than those of alkanes. δ- Hydrogen bond δ+ δ- δ+ Intermolecular dipolar δ- δ+ Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  8. Hydrogenation Rxn – Aldehydes Aldehyde hydrogenation rxn Alcohol oxidation rxn Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  9. Hydrogenation Rxn – Aldehydes Aldehyde hydrogenation rxn butanal 1-butanol 3,4-dimethylhexanal 3,4-dimethyl-1-hexanol Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  10. Hydrogenation Rxns – Ketones Ketone hydrogenation rxn Alcohol oxidation rxn Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  11. Hydrogenation Rxns – Ketones Ketone hydrogenation rxn 2-butanone 2-butanol 4,4-dimethyl-3-hexanol 4,4-dimethyl-3-hexanone Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  12. Addition of alcohol to aldehydes and ketones Hemiacetal intermediate acetal Hemiketal intermediate ketal • Hemiacetal is unstable, hard to isolate. • With excess alcohol and an acid catalyst, a stable acetal is formed. • Note the bidirectional arrows

  13. Hydrolysis of acetals and ketals acetal alcohol aldehyde ketal alcohol ketone • “Cutting by water” is essentially the reverse of the addition of alcohol to either aldehyde or ketone.

  14. Intramolecular addition of alcohols to aldehyde H O C CH2OH 1 6 * H OH C H OH O C 5 2 R H C HO H C C 1 OH H 4 3 H C OH C C 4 3 2 OH H H C OH 5 H OH CH2 OH 6 Intramolecularhemiacetal glucose • C1 is hemiacetal carbon. • Attached to it you will find: H, OH, OR and R, just like non-cyclical compounds.

  15. Aldehyde Rxns – Testing for Aldehydes Tollens’ Reagent (reacts with all aldehydes, but not ketones) Benedict’s Reagent (reacts with aldehydes, alpha-hydroxy ketones) • Benedict’s Reagent reacts with ketones that have an alcohol on the adjacent carbon (e.g., glucose) • Products include a red precipitate of copper (I) oxide

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