Nuclear Magnetic Resonance Spectroscopy. Barriers to Internal Rotation in Some Halogenated Methylbutanes

Barriers to internal rotation about the C(2)-C(3) bonds have been determined for ten closely related halogenated methylbutanes by detailed line-shape analysis of their nuclear magnetic resonance spectra. The experimental barriers range from 9 to 16 kcal/mol. In addition, for some of the compounds investigated, free energy differences were obtained for rotational isomers under conditions of slow conformational exchange. The results are discussed in terms of possible contributing nonbonded interactions