A STUDY ON THE STRUCTURE OF THE CYCLOPENTADIENYL ANION WITH C¹⁴ AS TRACER

Starting with formaldehyde-C¹⁴, 1,2-dibromocyclopentane-4-C¹⁴ (XI) was synthesized in eight steps. Conversion of XI to cyclopentadiene was accomplished in three different ways, namely: the dehydrobromination of XI with quinoline at 195–198 °C, the preparation of 1,2-bis-(trimethylammonium)-cyclopentane-4-C¹⁴ hydroxide from XI followed by thermal decomposition, and the conversion of XI to 3,5-dibromocyclopentene followed by reaction of the latter with magnesium in dry ether. Degradations of the samples of cyclopentadiene obtained by these three synthetic routes showed a completely randomized distribution of the C¹⁴ activity, with 20% of the total activity on each of the five carbon positions. These results led to the conclusion that these preparations of cyclopentadiene very likely involved ionization to the cyclopentadienyl anion. The randomized distribution of C¹⁴ in the resulting products thus furnishes a strong indication that all five carbon positions in the cyclopentadienyl anion are equivalent.