Allyl anions in solution

The rotational barriers of allylpotassium 23c (16.7 kcal/mol) and allylcesium 23d (18.0 kcal/mol) are much higher than those of 23 a and 23b. This observation and the question ofwhether aggregates are involved in the rotational process, clearly emphasize once more the important influence of the gegenion in carbanion reactions. The experimental results with 23a-d thus lead only to a lower limit (18.0 kcal/mol) for the rotational barrier of the allyl anion in solution. Incidently, this value comes close to the lowest calculated (MP2/4-31 + G//4-31 + G) value of the allyl anion rotational barrier (22.2 kcal/mol)33). 

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