Proposal for Sets of 77Se NMR Chemical Shifts in Planar and Perpendicular Orientations of Aryl Group and the Applications

The orientational effect of p-YC(6)H(4) (Ar) on delta(Se) is elucidated for ArSeR, based on experimental and theoretical investigations. Sets of delta(Se) are proposed for pl and pd employing 9-(arylselanyl)anthracenes (1) and 1-(arylselanyl)anthraquinones (2), respectively, where Se-C(R) in ArSeR is on the Ar plane in pl and perpendicular to the plane in pd. Absolute magnetic shielding tensors of Se (sigma(Se)) are calculated for ArSeR (R = H, Me, and Ph), assuming pl and pd, with the DFT-GIAO method. Observed characters are well reproduced by the total shielding tensors (sigma(t)(Se)). The paramagnetic terms (sigma(P)(Se)) are governed by sigma(P)(Se)(xx) + sigma(P)(Se)(yy), where the direction of n(P)(Se) is set to the z-axis. The mechanisms of the orientational effect are established both for pl and pd. Sets of delta(Se: 1) and delta(Se: 2) act as the standards for pl and pd, respectively, when delta(Se) of ArSeR are analyzed based on the orientational effect.