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A simple procedure for perfonning a mixed aldol condensation between symmetrical ketones and aromatic aldehydes has been published previously in this Journal (1). NMR and IR analyses of recrystallized product generally supports a symmetrical product of peneral structure 1 (the trans stereochemistry usually cannot usually be inferred by normal NMR or IR techniques). When 3-pentanone was reacted with p-chlorobenzaldehyde, however, we found the reaction roceeded smoothly to produce 2. This product was a surprise to the students and challenged their pectral interpretation and mechanistic skills.
The spectral features of 2 clearly support its structure. The infrared spectrum (Nujol mull) showed a tronp band at 1705 cm sup -1 attributable to an unconjugated carbonyl along with aromatic bands at 1600 and 825cm sup...