Microwave spectrum, torsional frequency and barrier to internal rotation in phenylboron difluoride

Abstract

Microwave spectra of the ground and first three excited torsional states of C₆H₅¹¹BF₂ and for the ground and first two excited torsional states of C₆H₅¹⁰BF₂ have been assigned. The variation of the inertial defect with torsional quantum number shows the molecule to be planar. The torsional frequency has been determined as ν= 49 cm^–1 and the barrier to internal rotation as Y₂= 1114 cm^–1(13.3 kJ mol^–1). With the assumption of a regular benzene ring (r_C—C= 1.397 Å and r_C—H= 1.084 Å) the geometry of the rest of the molecule is calculated to be r_C—B= 1.551 Å, r_B—F= 1.330 Å and FBF = 116.0°.