The MNDO method was used to study the extremal points on the potential energy surface of the reaction of bromine and 1-heptene. The formation of 1,2-dibromoheptane is energetically favored relative to formation of 1-bromo-2-heptene. (H2O)nHBr associates reduce the activation energy of the transition state and act as a strong catalytic agent for the molecular reaction. Lvov Research Institute of Judicial Examination, 7 Soborna pl., Lvov 290004, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 4, pp. 239–243, July–August, 1998.