By means of nonempirical quantum-chemical approximations RHF//STO-3G, 3-21G, and 6-31G(d) conformational characteristics were studied of molecular associate of 2-methyl-1,3,2-dioxaborinane with water (1:1). A possibility of formation of two-types of complexes was demonstrated: with a donor-acceptor bond O -> B and with an intermolecular hydrogen bond OHaEuro broken vertical bar O. The calculated parameters of their relative stability and conformational behavior depend both on the reciprocal orientation of the molecules under investigation and on the concepts of the approximation used for the calculation.