Stereochemistries of electron impact induced hydrogen abstraction reactions proceeding through 6‐membered transition states

The stereochemistries of nine electron‐impact induced eliminations proceeding from derivatives of thecis‐4‐t‐butyl system have been determined. The predominantciselimination observed in every case is consistent with the substantial integrity of the cyclohexyl ring prior to fragmentation, and with a cyclic transition state for hydrogen abstraction. The stereochemistries of electron impact induced eliminations from 11 derivatives of thetrans‐4‐t‐butylcyclohexyl system exhibit a dichotomy. The predominatntransstereochemistry observed in six electron impact induced eliminations, and the nonstereospecific electron impact induced dehydration oftrans‐4′‐t‐butylcyclohexyl‐ethanol are consistent with nonconcerted elimination from a chair‐like cyclohexyl ring. Conversely, the McLafferty rearrangement oftrans‐4′‐t‐butyl‐cyclohexyl‐2‐propanone proceeds nonstereospecifically.trans‐4‐t‐Butylcyclohexyl acetaldehyde, 2‐methyl‐3‐(trans‐4′‐t‐butylcyclohexyl)‐1‐propane andtrans‐4‐t‐butylcyclohexyl‐S‐methyl xanthate exhibit predominantcisMcLafferty rearrangement stereochemistry. This result may be due to fragmentation through boat‐like conformers in these compounds.