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NCERT Class XII Chemistry
Chapter - Aldehydes, Ketones and Carboxylic Acids
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Question : 9 of 28
Marks: +1, -0
Write structural formulas and names of four possible aldol condensation products from propanal and butanal. In each case, indicate which aldehyde acts as nucleophile and which as an electrophile
Solution:  
The possible products of aldol condensation from propanal and butanal are
(i)  2 CH3CH2CHOPropanal  →dil O−H  H3CCH2C∣OH  HC∣CH3HCHO3-Hydroxy-2-methylpentanal\text{(i)}\;\underset{\text{Propanal}}{2\,\mathrm{CH_3CH_2CHO}}\;\xrightarrow{\text{dil }\overset{-}{\mathrm{O}}\mathrm{H}}\;\underset{\text{3-Hydroxy-2-methylpentanal}}{\overset{\mathrm{OH}}{\overset{\vert}{\mathrm{H_3CCH_2C}}}\;\overset{\mathrm{CH_3}}{\overset{\vert}{\mathrm{HC}}}\mathrm{HCHO}}
(ii)  2 CH3(CH2)2CHOButanal  →dil O−H  H3C(CH2)2−C∣OHH−C∣CH2CH3HCHO2-Ethyl-3-hydroxyhexanal\text{(ii)}\;\underset{\text{Butanal}}{2\,\mathrm{CH_3(CH_2)_2CHO}}\;\xrightarrow{\text{dil }\overset{-}{\mathrm{O}}\mathrm{H}}\;\underset{\text{2-Ethyl-3-hydroxyhexanal}}{\mathrm{H_3C(CH_2)_2-}\overset{\mathrm{OH}}{\overset{\vert}{\mathrm{C}}}\mathrm{H-}\overset{\mathrm{CH_2CH_3}}{\overset{\vert}{\mathrm{C}}}\mathrm{HCHO}}
(iii) When butanal acts as an electrophile and propanal as nucleophile :
H3C(CH2)2CHOButanal+CH3CH2CHOPropanal→O−HH3C(CH2)C∣OHHC∣CH3HCHO3-Hydroxy-2-methylhexanal\underset{\text{Butanal}}{\mathrm{H_3C(CH_2)_2CHO}} + \underset{\text{Propanal}}{\mathrm{CH_3CH_2CHO}} \xrightarrow{\overset{-}{\mathrm{O}}\mathrm{H}} \underset{\text{3-Hydroxy-2-methylhexanal}}{\mathrm{H_3C(CH_2)}\overset{\mathrm{OH}}{\overset{\vert}{\mathrm{C}}}\underset{\mathrm{CH_3}}{\underset{\vert}{\mathrm{HC}}}\mathrm{HCHO}}
(iv) When propanal serves as an electrophile and butanal as nucleophile :
CH3CH2CHO+CH3(CH2)2CHO→H3CCH2C∣OHH−C∣C2H5HCHO2-Ethyl-3-hydroxypentanal\mathrm{CH_3CH_2CHO} + \mathrm{CH_3(CH_2)_2CHO} \rightarrow \underset{\text{2-Ethyl-3-hydroxypentanal}}{\overset{\mathrm{OH}}{\overset{\vert}{\mathrm{H_3CCH_2C}}}\mathrm{H-}\overset{\mathrm{C_2H_5}}{\overset{\vert}{\mathrm{C}}}\mathrm{HCHO}}
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