Large Amplitude Motions in 2,3-Dimethylfluorobenzene: Steric Effects Failing to Interpret Hindered Methyl Torsion

The microwave spectrum of 2,3-dimethylfluorobezene, one the six isomers dimethylfluorobenzene, was recorded using a pulsed molecular jet Fourier transform spectrometer operating in frequency range from 2 to 26.5 GHz. internal rotations two inequivalent methyl groups, causing splittings up several hundred MHz all rotational energy levels into quintets, were analyzed and modeled. torsional barriers groups at ortho meta positions determined be 215.5740(56) cm–1 488.53(11) cm–1. A comparison with barrier heights observed for 2,6-dimethylfluorobenzene 3,4-dimethylfluorobenzene has shown that group position seems invisible its neighboring ortho-methyl group, while meta-methyl clearly senses one. Steric effects are not able explain this observation, electrostatic most probably reason. Highly accurate parameters experimentally compared those obtained quantum chemical calculations different theory.