Nuclear Magnetic Resonance Spectroscopy. Variable-Temperature C and F Study of the Chair-Chair Interconversion of 1,1,3,3-Tetramethylcyclohexane and gem-Difluoro-1,1,3,3-Tetramethylcyclohexanes

A variable-temperature, proton noise-decoupled, (13)C nmr spectral study of the chair-chair interconversion in 1,1,3,3-tetramethylcyclohexane has demonstrated the utility of (13)C spectra for probing conformational equilibria. There is a much larger chemical-shift difference between the carbons of axial and equatorial methyl groups than between the protons of these methyl groups, 133 Hz compared to 7.5 Hz. Comparison of the activation parameters determined from the (13)C spectra of 1,1,3,3-tetramethylcyclohexane with those determined from a variable-temperature (19)F study on 2,2,6,6-tetramethyl-1,1-difluorocyclohexane shows that the introduction of a gem-difluoro group into the ring causes significant steric interactions. The (13)C chemical shifts for 1,1,3,3-tetramethylcyclohexane reflect the importance of the methyl-methyl 1,3-diaxial interactions.

Flexion fracture of the lumbar spine due to lap-type seat belts

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Decompressive laminectomy for low back and sciatic pain

A proportion of patients with lumbar disc syndromes have little in the way of disc protrusion, but have spinal canals, either congenitally narrow, or else narrowed by degenerative changes. These patients require myelography for their assessment and decompression by complete laminectomy for their treatment, as opposed to the more usual practice of discectomy via partial laminectomy and/or fusion. Five such cases with myelographic findings are presented.