THE EFFECTS OF DEUTERIUM SUBSTITUTION ON THE RATES OF ORGANIC REACTIONS. IX. BRIDGEHEAD $beta$-DEUTERIUM IN A CARBONIUM ION SOLVOLYSIS

The bicyclic tertiary chloride 11-methyl-11-chloro-9, 10-dihydro-9,10- ethanoanthracene and its -12,12-d2 and -9,10-d/sub 2/ analogs were synthesized and their solvolysis rates measured in 60% aqueous ethanol at 45 deg . While the for a carbonium ion solvolysis (k/sub H//k/sub D/ = 1.14), the bridgehead deuterated analog (-9,10-d/sub 2/) exhibits an isotope effect, k/sub H//k/sub D/ = 0.988, not appreciably different. It was concluded that the BETA -deuterium isotope effect is strongly dependent on the spatial orientation of the isotopic bond. This is consistent with the earlier suggestion that hyperconjugative intramolecular transmission of electronic charge is an essential factor in causing BETA -deuteriumsubstituted compounds to give slower carbonium ion type reactions than their protium analogs. Inductive interactions seem to cause a much smaller effect, possibly in the opposite direction. (auth)