A theoretical comparison of the chemical shifts of three related heterocycles: 1H-pyrazoles, 1H-1,2,4-triazoles and 1H-1,2,4-diazaphospholes

Seventeen derivatives of 1H-pyrazoles, 1H-1,2,4-triazoles and 1H-1,2,4-diazaphospholes (three of them existing in two tautomeric forms, thus forming 20 families of compounds) were studied theoretically. At the GIAO/B3LYP/6-311++G(d,p) level, the calculations reproduce fairly well the available experimental chemical shifts. The completeness of the calculated absolute shieldings allows to discuss the relationships between the 4-position (CH, C, N and P) chemical shifts. There are noticeable differences due to the different contributions of the substituents at positions 3 and 5.