\(\underset{propanal}{\mathop{C{{H}_{3}}C{{H}_{2}}CHO}}\,\)                   \(\underset {trichloroethanal}{\mathop {Cl_3CCHO}}\)

\(\underset {methanal} {\mathop {HCHO}}\)                   \(\underset {ethanal} {\mathop CH_3CHO}\)

\(\underset {benzaldehyde} {\mathop {C_7H_6O}}\)

Trichloroethanal, methanal and benzaldehyde do not undergo aldol condensation. Aldol condensation is not given by aldehydes and ketones which do not contain \(\alpha \) - hydrogen atom \((s)\).