Theoretical structure determination of a class of heterocyclic compounds: The pyrazolidines

Theoretical calculations at the B3LYP-D3(BJ)/6–311++G(d,p) level of a series of 35 neutral pyrazolidines and 3 protonated derivatives have been carried out for different conformers generated using the CREST program. Seven optimized geometries were compared with X-ray determined structures and their 1H and 13C GIAO calculated chemical shifts with experimental results. The remaining pyrazolidines were compared with the available NMR information. The core of the present paper is the use of the pseudorotational wheel of Cremer and Pople to discuss the experimental and calculated conformation of the five-membered ring.