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Question
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 electrophile.
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Solution
The possible products of aldol condensation from propanal and butanal are:
(i) \[\begin{array}{cc}
\phantom{..............................}\ce{OH}\phantom{...}\ce{CH3}\\
\phantom{...........................}|\phantom{.....}|\\
\ce{\underset{Propanal}{2CH3CH2CHO}->[dil.\overset{-}{O}H]\underset{3-Hydroxy-2-methylpentanal}{H3C - CH2 - CH - CH - CHO}}\\
\end{array}\]
(ii) \[\begin{array}{cc}
\phantom{.......................................}\ce{OH}\phantom{..}\ce{CH2CH3}\\
\phantom{................................}|\phantom{.....}|\\
\ce{\underset{Butanal}{2CH3(CH2)2CHO}->[dil.\overset{-}{O}H]\underset{2-Ethyl-3-hydroxyhexanal}{H3C - (CH2)2 - CH - CH - CHO}}\
\end{array}\]
(iii) When butanal acts as an electrophile and propanal as a nucleophile:
\[\begin{array}{cc}
\phantom{...........................................}\ce{OH}\\
\phantom{.........................................}|\\
\ce{\underset{Butanal}{H3C - (CH2)2CHO} + \underset{Propanal}{CH3CH2CHO}->[\overset{-}{O}H]H3C - (CH2)2 - CH - CH - CHO}\\
\phantom{.....................................................}|\\
\phantom{.........................................................}\ce{\underset{3-Hydroxy-2-methylhexanal}{CH3}}\
\end{array}\]
(iv) When propanal serves as an electrophile and butanal as a nucleophile:
\[\begin{array}{cc}
\phantom{............................................}\ce{OH}\phantom{...}\ce{C2H5}\\
\phantom{.........................................}|\phantom{......}|\\
\ce{CH3CH2CHO + CH3(CH2)2CHO -> \underset{2-Ethyl-3-hydroxypentanal}{H3C - CH2 - CH - CH - CHO}}\
\end{array}\]
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