DEUTERIUM-INDUCED ISOTOPE EFFECTS OF A C-H-CENTER-DOT-CENTER-DOT-CENTER-DOT-SE HYDROGEN-BOND ON THE IR AND NMR-SPECTRA OF 6H,12H-DIBENZO[B,F][1,5]DISELENOCIN

Deuterium-induced isotope effects of the C-H ... Se nonbonded interact ion of 6H,12H-dibenzo[b,f][1,5]diselenocin (1) were investigated. The IR spectroscopic behavior of 6H,12H-dibenzo[b, f][1,5]diselenocin-6,6, 12,12-d(4) (1-d(4)) was compared with that of the reference compound ( benzyl-alpha,alpha-d(2) phenyl selenide (2-d(2))). The results for bot h boat (1B) and chair (1C) conformers of 1 indicated that the C-H ... Se interaction causes the decrease in the low wavenumber shift of nu(1 ) (Delta nu(1) = -2 cm(-1) for 1B-d(4) and -12 cm(-1) for 1C-d(4), whe reas Delta nu(1) = -15 cm(-1) for 1B and -52 cm(-1) for 1C). The (77)S eNMR showed the upheld isotope shift due to the through-space C-H ... Se interaction (Delta Delta delta = 0.44 ppm for 1B and 0.25 ppm for 1 C). These findings clearly suggested that the interaction is attractiv e in nature. MO calculations at the HF/3-21G level and NBO analysis s howed the importance of the electron delocalization from the selenium lone pair to the antibonding orbital of the C-H bond. These observatio ns strongly suggested that the interaction be called a C-H ... Se hydr ogen bond.