AbstractFourier transform Raman and infrared spectra have been recorded of diazepam (7‐chloro‐1,3‐dihydro‐1‐methyl‐5‐phenyl‐2H‐1,4‐benzodiazepin‐2‐one) and four compounds with closely related structures. These compounds are all 7‐chloro‐1,3‐dihydro‐5‐phenyl‐2H‐1,4‐benzodiazepin‐2‐ones and differ only in the nature of the substituent (R) at N‐1. The five compounds are nordazepam (R  H), diazepam (R  CH3), pinazepam (R  CH2CCH), halazepam (R  CH2CF3) and prazepam (R  cyclopropylmethyl). Prominent features of the infrared and Raman spectra have been assigned to functional groups of the parent structure and the substituent groups. The spectra of nordazepam suggest that the compound exists as a centrosymmetric cyclic dimer in the solid state. Complete tabulations of the observed wavenumbers of the five molecules are given. The