The atropisomeric and conformationalproperties of 1,5-benzodiazepines with an N-sulfonyl (p-tosyl/mesyl) group (IIa/b) were investigated by comparison with those of the N-benzoyl congeners (I). Similar to I, when the Ar–N(SO2) axis was frozen by a C9-substitution in the molecules, IIa/b were separated into the (aR)- and (aS)-atropisomers. The conformation of IIa/b revealed that the substituent (p-tolyl/methyl