Dynamic 13C NMR studies on the internal rotation in tetraarylallyl anions

Proton noise decoupled 13C NMR spectra of lithium 1,1,3,3-bis (2,2′-biphenylylene)propenide and lithium 1,1,3,3-tetraphenylpropenide have been studied, and complete assignments have been made based on several methods, e.g. 13C13C coupling constants of selectively labelled compounds and low-temperature splitting of temperature dependent signals. The barriers to rotation about the partial double bonds of the allyl group have been determined by 13C DNMR resulting in the thermodynamic parameters of activation ΔG = 57 kj mol−1, ΔH≠ = 56.5 kj mol−1, ΔS≠ = −3J mol−1K−1 and ΔG = 55.5 kj mol−1, ΔH≠ = 63 kj mol−1, ΔS≠ = 26 kJ mol−1K−1, respectively. The results are discussed, including the hitherto known data about the topomerisation process.