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

$\underset {methanal} {\mathop {HCHO}}$                   $\underset {ethanal} {\mathop CH_3CHO}$

$\underset {benzaldehyde} {\mathop {C_7H_6O}}$

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 $(s)$.