The room-temperature crystal structures of eighteen compounds are reported. (2) symmetry. There are only three exceptions to this non-mixing rule among thirty-odd of the many propellane structures reported in the literature. The considerable deviations found from ideal conformations are ascribed to crystal packing effects and, for molecules with n = 1 and 2, to the deviations from tetrahedrality at the bridgehead atoms; this serves to explain the 'Klammer' effect. The lowest-energy conformations from molecular-mechanics calculations are generally those found experimentally.

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A stereospecific 180-labelling study shows that the syn-hydroxy group is preferentially lost from the syn,anti-title diol upon i-C 4HlO chemical ionization, indicating occurrence of a stereoelectronic effect in this process. A collision-induced dissociation study of deuterium-and 180-1abelled analogs shows that a symmetrical ether structure is not formed in the above process by an SNimechanism. This result leads to the conclusion that the stereoelectronic assistance of the anti-OH group in the loss of the syn-hydroxyl is expressed either in a weak transition state interaction or by other processes such as f3-elimination via hydrogen transfer with concomitant double bond formation.

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The title compounds have been isolated and their structures determined by X‐ray crystallography. Their relative stability is discussed in terms of theory and experiment. The endo‐adduct is the thermodynamically more stable one.