ALDEHYDES AND KETONES: NUCLEOPHILIC ADDITION TO THE CARBONYL GROUP 435 17.19 (a) First consider all the isomeric aldehydes of molecular formula CsHioo. Pentanal 3-Methylbutanal H (S)-2-Methylbutanal (R)-2-Methylbutanal 2, 2-Dimethylpropanal There are three isomeric ketones. 2-Pentanone 3-Pentanone 3.Methyl-2-butanone (b) Reduction of an aldehyde to a primary alcohol does not introduce a stereogenic center into the molecule. The only aldehydes that yield chiral alcohols on reduction are therefore those that already contain a stereogenic center. H OH CH,OH (S)-2-Methylbutanal (S)-2-Methyl-1-butanol (R)-2-Methylbutanal (R)-2-Methyl-l-butanol Among the ketones, 2-pentanone and 3-methyl-butanone are reduced to chiral alcohols 2-Pentanone 2-Pentanol (chiral but racemic OH 3-Pentanone 3-Pentanol 3-Methyl-2-butanone Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website17.19 (a) First consider all the isomeric aldehydes of molecular formula C5H10O. There are three isomeric ketones: (b) Reduction of an aldehyde to a primary alcohol does not introduce a stereogenic center into the molecule. The only aldehydes that yield chiral alcohols on reduction are therefore those that already contain a stereogenic center. Among the ketones, 2-pentanone and 3-methyl-butanone are reduced to chiral alcohols. NaBH4 CH3OH O 3-Methyl-2-butanone OH 3-Methyl-2-butanol (chiral but racemic) NaBH4 CH3OH O 3-Pentanone OH 3-Pentanol (achiral) NaBH4 CH3OH O 2-Pentanone OH 2-Pentanol (chiral but racemic) (R)-2-Methylbutanal (R)-2-Methyl-1-butanol NaBH4 CH3OH H O H OH H H (S)-2-Methylbutanal (S)-2-Methyl-1-butanol NaBH4 CH3OH O OH H H 2-Pentanone 3-Pentanone 3-Methyl-2-butanone O O O H H (S)-2-Methylbutanal O (R)-2-Methylbutanal O 2,2-Dimethylpropanal H H H O O H Pentanal O H 3-Methylbutanal ALDEHYDES AND KETONES: NUCLEOPHILIC ADDITION TO THE CARBONYL GROUP 435 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website