An aldol condensation reaction can take place between two of the same aldehydes or ketones (known as self-condensation) or between two unique aldehydes or ketones (known as crossed aldol condensations). A crossed aldol condensation between acetophenone and pivalaldehyde is shown below. Notice that acetophenone has only one alpha carbon (three acidic hydrogen atoms) whereas pivalaldehyde has no protons on the alpha carbon and can only act as an electrophile in this crossed aldol.
NaOH (cat)
EtOH C(CH3)3
C(CH3)3
acetophenone
pivalaldehyde
(E)-4,4-dimethyl-1-phenylpent-2-en-1-one
In this lab, you will run a crossed aldol reaction using benzaldehyde and acetone: Because acetone has two alpha carbons, it will condense with two molecules of benzaldehyde (one condensation per side), depending on reaction conditions.
NaOH (cat)
Ph
HzC
"CH3 EtOH
Ph Ph dibenzylideneacetone
benzaldehyde
acetone
CH3