Quantum chemical calculations of NMR chemical shifts of organic molecules: XI. Conformational and relativistic effects on the 31P and 77Se chemical shifts of phosphine selenides

Conformational and relativistic effects on the ³¹P and ⁷⁷Se chemical shifts of phosphine selenides were analyzed in terms of the ZORA-GIAO-B1PW91/TZP approach. The effect of conformation of phosphine selenides related to internal rotation about the single P-C bonds was found to be insignificant, while the contribution of relativistic spin-orbit interaction to the calculated values of ⁷⁷Se chemical shifts did not exceed 10 ppm. On the other hand, relativistic effects arising from magnetic shielding of the phosphorus nucleus in the P=Se fragment by selenium are fairly strong (25–30 ppm), which indicates the necessity of including the contribution of relativistic spin-orbit interaction in the calculation of ³¹P chemical shifts in phosphine selenides.