A theoretical study of inversion barriers and NMR chemical shifts of 3-pyrazolines (2,3-dihydro-1H-pyrazoles)

A rather neglected family of heterocyclic compounds, the 3-pyrazolines or 2,3-dihydro-1H-pyrazoles, has been studied theoretically at the B3LYP/6-311++G(d,p) level to obtain geometries and energies and at the GIAO/B3LYP/6-311++G(d,p) level for NMR chemical shifts. The calculated barriers of inversion of the N-substituents reproduce adequately the scarce experimental data. The calculated H-1 and C-13 chemical shifts are consistent with those reported in the literature. A combination of both results, geometries, and C-13 chemical shifts, shed light on the conformation of N-phenyl groups.

Automated summary

The neglected family of 3-pyrazolines or 2,3-dihydro-1H-pyrazoles was studied theoretically, with calculations at the B3LYP/6-311++G(d,p) level for geometries and energies and at the GIAO/B3LYP/6-311++G(d,p) level for NMR chemical shifts. The calculated barriers of inversion of N-substituents showed good agreement with experimental data, and H-1 and C-13 chemical shifts were consistent with literature values. The combination of geometry results and C-13 chemical shifts provided insights into the conformation of N-phenyl groups.