Question

Which of the following compounds would be the main product of an aldol condensation of acetaldehyde and acetone ?

• A. $ CH_3CH = CH \cdot CHO $
• B. $ CH_3CH = CHCOCH_3 $
• C. $ (CH_3)_2C = CH \cdot CHO $
• D. $ (CH_3)_2C = CHCOCH_3 $

Answer 1

Answer: (B)

When aldehydes condense with ketones, it is the $\alpha$ -hydrogen atom of the ketone which involved in the aldol condensation.

$CH _{3} CHO + HCH _{2} COCH _{3} \ce{->[{ NaOH }]}$

$\underset{\text{major}}{CH _{3} CH ( OH ) CH _{2} COCH _{3}} + CH _{3} CH ( OH ) CH _{2} CHO +\left( CH _{3}\right)_{2} C ( OH ) CH _{2} COCH _{3} +\left( CH _{3}\right)_{2} C ( OH )- CH _{2} CHO$

$\underset{\text{major product}}{CH _{3} CH ( OH ) CH _{2} COCH _{3}} \ce{->[{\Delta}][{-H_2O}]} \underset{\text{major product} (25 \%)}{CH _{3} CH = CHCOCH _{3}}$