Quantum-chemical investigation of monosubstituted cyclopropanes

The applicability of the semiempirical MINDO/3 and MNDO methods is demonstrated for the determination of the relative changes in the strain of the three-carbon ring and examination of the contributions from the effects of substituents X to the stabilization energy of monosubstituted cyclopropanes (substituents H, OCH₃, NH₂, F, Cl, CH₃, CF₃, COCH₃, CN, NO₂). The best results, comparable with the data from nonempirical calculations, were obtained by the MINDO/3 method. The method correctly confers the changes in the geometry of substituted cyclopropane rings but systematically underestimates the strain energy by 20–40 kJ/mole. To judge from the AE_strain values, the -accepting effect of the substituents NO₂, COCH₃, and CN plays a major role in determining the electronic structure, suppressing the destabilizing -acceptor effect. In the case of the substituents F, Cl, OCH₃, and NH₂ the stabilizing -donor effect is either completely suppressed or is partly balanced by the -acceptor effect.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 21, No. 4, pp. 399–407, July–August, 1985.