An investigation of the molecular dynamics of substituted 1,3,4,5-tetrahydro-2H-l,Ibenzodiazepin-2-0ne derivatives revealed that these molecules adopt cycloheptadiene-like boat conformations. There is an equilibrium between the quasi-axial and the quasiequatorial conformer in which the quasi-axial conformer is predominant. The difference in their conformational energies is less than 1 kcal mol-'. 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.