The conformational equilibrium in solution was examined by NMR spectroscopy for a series of 7α phenyl 3 borabicyclo[3.3.1]nonane derivatives containing various substituents at the boron atom. The structures of these derivatives were studied in the crystalline state (X ray diffraction analysis) and by quantum chemical calculations (B3Pw91/6 31G*). The B...Ph transannular interactions corresponding to charge transfer from the π system of the phenyl group to the vacant p orbital of the B atom were demonstrated to be responsible for unique stability of the chair-chair conformation of these derivatives.