1‐Cyclohepta‐2,4,6‐trienyl‐selanes—a 77 Se NMR study: Indirect nuclear 77 Se 13 C spin–spin coupling constants and application of density functional theory (DFT) calculations

1‐Cyclohepta‐2,4,6‐trienyl‐selanes Se(C 7 H 7 ) 2 (2c), RSeC 7 H 7 with R = Bu, t Bu, Ph, 4‐FC 6 H 4 (12a,b,c,d) were prepared by the reaction of the corresponding silanes, Si(SeMe 3 ) 2 and RSeSiMe 3 , respectively, with tropylium bromide C 7 H 7 Br. In spite of the low stability of the selanes even in dilute solutions and at low temperature, they could be characterised by their 1 H, 13 C and 77 Se NMR parameters. Coupling constants 1 J ( 77 Se, 13 C) were measured and calculated by DFT methods at the B3LYP/6‐311+G(d,p) level of theory. The comparison of experimental and calculated coupling constants 1 J ( 77 Se, 13 C) included numerous selenium carbon compounds with largely different SeC bonds, revealing a satisfactory agreement. Both the spin–dipole (SD) and the paramagnetic spin‐orbital (PSO) terms contributed significantly to the spin–spin coupling interaction, in addition to the Fermi contact (FC) term. Copyright © 2006 John Wiley & Sons, Ltd.