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RECEIVED SEPTEMBER 21, 1961The n.m.r. spectra of a number of bicyclo[2.l.l]hexane derivatives have been examined and may be interpreted consistently using one set of coupling constants.In the study of n.m.r. spectra, rigid systems such as that found in bicyclic compounds are of particular interest since they afford an opportunity to investigate the correlation between the spectral parameters and the geometry of the molecule. The bicyclo [Z.l.l]hexane derivatives which were available from a previous investigation* have therefore been examined. For convenience in the following discussion, the various protons will be designated and the substituent will replace either or both of a' and b'.The spectra of key compounds, endo-bicyclo-[2.1,1 ]hexane-5-01 (l), exo-bicyclo [2.l. llhexane-5-01 (2), bicyclo [2.1.1 ]hexane-5-one (3) and bicyclo-[2.l.l]hexane (4) are shown in Fig. 1. It will be convenient to consider the spectrum of 1 first. The doublet at r = 9.40 is the band shifted farthest upfield and has an area corresponding to one proton. This must correspond to a, b, or b', for all other protons come in pairs. I t cannot be b' since this would be shifted down field due to the hydroxy group, and presumably appears at r = 6.52.The band corresponding to the other nieinber of the pair a and b appears at r = 9.10. It is a doublet, each member of which has been split further by the influence of other protons, presumably c (7 = 7.63). I t would be expected to give two triplets, but appears to have more coniponents. OH H 1 2 1 n ' 0 3 4 (1) This work was supported by the U. S. Army Research Office (2) K. B. Wiberg and B. R. Lowry, J . Am. Chcm. Soc., 84, in (Durham).preess (1962).A confirmation of this assignment may be found in the relative intensities in the upfield doublet. The chemical shift between a and b is 18 set.-' and the coupling constant is 7.6 sec.-l. The relative intensity for the outside to the central line in an AB case is given by where Av is the chemical shift. Csing the above values, the relative intensity was calculated to be 0.49, whereas the average ratio for several spectra taken at different times was 0.46.A decision as to which band arises from a niay be made by considering the geometry of the molecule as deduced from molecular models.Looking down the Cl-Ca bond, the arrangement of a, b and c will be C I The correlation between coupling constants and dihedral angles is well established : The coupling constant is maximum a t 0' (-8 sec.-l) and lSO0 (-10 sec.-l) and minimum at 90' (-0 ~e c . -l ) .~ The coupling between a and c mill then be negligible, and that between c and b will be on the order of 3-4 set.-'. The upfield doublet n;ust then arise from a, and the split doublet arises from b. This analysis also shows that the band a t r = 7.63 must arise from c, with J b c = 2.9 set.-'. The A2Bz system arising from d and e appears at 7 = 8.50. The shape of the band indicates that a t least one of the coupling constants between the four protons is large, but the spectruni is not well enough resolved to pe...

If one of these is to be associated with mechanism 16 it seems necessary to assume that IV is an intermediate in the interconversion of species I and II and that IV converts to I somewhat more rapidly than II; IV could readily convert to either of the two possible intermediates pictured above by conventional processes.

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