PRIMARY AND SECONDARY DEUTERIUM-INDUCED ISOTOPE EFFECTS FOR C-13 NMR PARAMETERS OF BENZALDEHYDE

Deuterium-induced isotope effects on C-13 chemical shifts and (1)J(C-13-alpha,H-1) coupling constants In benzaldehyde were measured Over 30 different effects on C-13 chemical shifts were revealed. The effects through one ((1) Delta) and two bonds ((2) Delta) have mean values of 282.1 +/- 9.6 and 109.5 +/- 3.1 ppb, respectively, which is consistent with previously observed trends. Exceptions are [alpha-H-2]benzaldehyde and [o-H-2]benzaldehyde, where (2) Delta values at the quaternary carbon C-1 of only 72.6 and 69.6 ppb, respectively, were determined. While (3) Delta at the C-2,6 site in [p-H-2]benzaldehyde is absent, three different (3) Delta effects in [o-H-2]benzaldehyde were observed. The longest range effect is (5) Delta = -1.9 ppb, observed in [p-H-2] benzaldehyde. The role of the position and the number of incorporated deuterium atoms with respect to the range, magnitude and sign of these effects is discussed. Some of the observed effects are rationalized through interactions with lone-pair electrons at the oxygen atom. A number of carbon-deuterium coupling constants, (n)J(C-13,H-2), through one, two and three bonds were measured. A single primary deuterium isotope effect on (1)J(C-13-alpha,H-1) in [alpha-H-2]benzaldehyde was determined, whereas no secondary effect through three or more bonds on the same coupling constant was observed