NMR spectra and conformational analysis of substituted 1,3,4,5‐tetrahydro‐2H‐1,5‐benzodiazepin‐2‐one derivatives

An investigation of the molecular dynamics of substituted 1,3,4,5‐tetrahydro‐2 H ‐1,5‐benzodiazepin‐2‐one derivatives revealed that these molecules adopt cycloheptadiene‐like boat conformations. There is an equilibrium between the quasi‐axial and the quasi‐equatorial conformer in which the quasi‐axial conformer is predominant. The difference in their conformational energies is less than 1 kcal mol −1 . The most important factor influencing the energy barrier between the conformers is the presence of a substituent other than hydrogen at N‐1. Our findings disprove earlier reports by other workers.