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-1 3-alpha,H-1) coupling constants In benzaldehyde were measured Over 30 different effects on C-13 chemical shifts were revealed. The effects t hrough one ((1) Delta) and two bonds ((2) Delta) have mean values of 2 82.1 +/- 9.6 and 109.5 +/- 3.1 ppb, respectively, which is consistent with previously observed trends. Exceptions are [alpha-H-2]benzaldehyd e and [o-H-2]benzaldehyde, where (2) Delta values at the quaternary ca rbon C-1 of only 72.6 and 69.6 ppb, respectively, were determined. Whi le (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] ben zaldehyde. The role of the position and the number of incorporated deu terium atoms with respect to the range, magnitude and sign of these ef fects is discussed. Some of the observed effects are rationalized thro ugh 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 determin ed, whereas no secondary effect through three or more bonds on the sam e coupling constant was observed