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THE classical stereochemists were familiar with the concept of boat and chair conformations 192 for cyclohexane. Only in the last decade has it become firmly established that the chair conformation is more stable 394 than the boat, although it is, of course, appreciated that the energy barrier separating the two forms is so low6 as to prevent investigation of the phenomenon by the classical stereochemical methods at the disposal of the organic chemist.The number of geometrically possible conformations becomes very much greater when the fusion of two cyclohexane rings to give trans-and cis-decalin is considered. Fortunately, if chair conformations are accepted as being more stable than boat conformations, then there is a unique conformation for both trans-(I) and cis-decalin ( 11). (I) is the conformation of transdecalin which has been accepted for many years, whereas (11) differs from the two-boat Sachse-Mohr cis-decalin conformation (111), which is usually depicted in the text books. Experimental evidence that (11) is the correct representation of cis-decalin has been obtained by the electron diffraction studies of Hassel and his colleagues 6 and is supported by chemical evidence.'

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