The Se-77 NMR chemical shifts (delta(obsd)(Se)) of p-YC6H4SeMe (1: Y = H (a), OMe (b), Me (c), Cl (d), Br (e), COOR (f), and NO2 (g)) and p-YC6H4SePh (2) were determined or redetermined in chloroform-d. The delta(obsd)(Se) values of 2, p-YC6H4SeR (R = CN (3), Bz (4), H (5), Br (6), Et (7), C6H4Y-p (8), CH=CH2 (9), CH =CHCl-t (10), and CHCH2CCl2-cyclo (11)), 1,1'-[8-(p-YC6H4Se)C10H6Se](2) (12), and 1-(MeSe)-8-(p-YC6H4Se)C10H6 (13) were plotted against those of 1. The plots were analyzed as two correlations. For example, the points corresponding to a-e make a group (g(m)), and those of d-g belong to another one (g(n)). This must be a reflection of the differences in the dihedral angles between the aryl rings and the Se-R bonds, which should result in the different contributions of the inductive and mesomeric effects of the substituents Y on the d,b,d(Se) values. After reexamination of the applicability of the GIAO magnetic shielding tensor for the selenium nucleus (sigma(Se)) in selenium compounds of various structures, a(Se) was calculated for the model compounds, 5, with the B3LYP/6-311+G(d,p) method, to explain the d,b,d(Se) values of 1-13 uniformly: delta(calcd)(Se) was defined as -(sigma(Se) -sigma(Se)(MeSeMe)). Each selenol was optimized to be the planar structure (14) or the perpendicular one (15). New parameters were devised such as delta(calcd)(Se:theta(B)) = (1 - sin theta(B))delta(calcd)(Se)(14) + sin (theta(B))delta(calcd)(Se)(15) The d,b,d(Se) values of 1-13 correlated well with the new parameters, delta(calcd)(Se:theta(B)), which gave the best-fitted theta(B) values. The structures of 1-13 in solutions were explained uniformly by the evaluated theta(B) values. The observed ratios of the slopes for g(m) versus those of g(n) were also correlated with the theta(B) values.