Abstract-Accurate parameters for the two title compounds have been obtained by the aid of a spectral subtraction technique in conjunction with analysis by LAOCN3. It is observed that Jleq,8eS and J1ax.zax are abnormally large and small, respectively, and the significance of these and other coupling constants are discussed in terms of the probable geometry of tert-butylcyclohexane. The tert-butyl group affects the chemical shifts of the 4-protons, indicating that tert-butylcyclohexyl derivatives are poor models for fixed conformers of monosubstituted cyclohexanes. The deuterium isotope effects on proton chemical shifts appear to be influenced by the same factors as proton-proton coupling constants.~-T~~~-BUTYLCYCLOHEXYL derivatives have played an important role in the development of the theory of conformational analysis of cyclohexane systems. A method frequently ~s e d l .~*~ for determining the equilibrium between the two rapidly exchanging chair conformers of simple cyclohexyl derivatives, utilizes chemical shift measurements on such averaged systems, together with values for the analogous protons in the epimeric 4-tert-butylcyclohexyl derivatives, it being assumed that the latter are satisfactory models for the fixed conformations. Low temperature NMR studies have, however, indicated that the chemical shifts for the 'pure' conformers are different from those of the model compound^.^*^*^ The origin of these discrepancies has not been determined, and several factors such as long-range shielding and geometric distortion might be implicated.There has been no direct determination of the geometry of tert-butylcyclohexane, although the electron diffraction study of cis-and trans-Ctert-butyl-1-chlorocyclohexane has been reported' and an X-ray diffraction structure determination has been carried out for cis-(pbromophenyl)-4-tert-butylcyclohexane.8 Several force field calculations of the structure of tert-butylcyclohexane have been published~~1° of which that by Altona and SundaralingamlO is the most complete.Recently, Remijnse, Van Bekkum and Wepster deduced all the chemical shifts of tert-butylcyclohexane, and four of the ten vicinal coupling constants, from the spectra of three tert-butylperdeuterocyclohexanes retaining cis vicinal pairs of protons, and from an incomplete analysis of the spectrum of tert-butylcyclohexane-3,3,5,5-~&.~l We now report complete analyses of this compound (2) and of the -3,3,4,4,5,5-d6 derivative (l), which confirm and augment the results of these workers.
EXPERIMENTALThe mass spectral data were obtained using an AEL-MS 9 mass spectrometer at 70 eV. Vapour phase chromatography (GLC) data were obtained using a Perkin-Elmer 881 Gas Chromatograph.All solvents used in the experiments described were distilled. Ether for use in lithium aluminum hydride reductions was dried by distillation from calcium hydride and stored over sodium wire.
4-tert-
tert-Butylcyclohexane-3,3,4,4,5,5-d, (1).A mixture of mossy zinc (1 g), mercuric chloride (0.3 g), DCl (0.1 ml, 38% in D,O, 99% D, Stohler Isotope Chem...
