Anomalous Chemical Shifts in the Proton Magnetic Resonance Spectra of the Dimethylcyclohexanes and Related Hydrocarbons
High-resolution proton magnetic resonance spectra were determined for the dimethylcyclohexanes and several related hydrocarbons between —130°C and 130°C. All of the compounds which should undergo rapid ring inversion at room temperature produce spectra which change on cooling because of “freezing out” of this motion. The assumption that appearance of the ring-hydrogen resonances as a relatively narrow band is invariably a symptom of rapid ring inversion is shown to be unfounded. Several of the ring spectra differ drastically from what is predicted using a bond-anisotropy model. A previously unrecognized effect, then, must make a significant contribution to the observed chemical shifts.
KeywordsProton Chemical Shift Raney Nickel Ring Hydrogen Ring Inversion Methine Hydrogen
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