DEUTERIUM AND O-18 ISOTOPE EFFECTS ON C-13 CHEMICAL-SHIFTS OF STERICALLY HINDERED AND OR INTRAMOLECULARLY HYDROGEN-BONDED O-HYDROXY ACYL AROMATICS/

A series of sterically hindered o-hydroxy aromatic ketones were synthe sized, including benzene, naphthalene, phenanthrene and pyrene derivat ives. Deuterium isotope effects on the C-13 chemical shifts of 2-hydro xy-1-acenaphthone and other sterically hindered, intramolecularly hydr ogen-bonded aromatic ketones (OH exchanged) are shown to be unusual. T he two-bond isotope effects are very large. Likewise ape the istope ef fects on C=0, C-1, C-3 and C-4 carbon resonances and some show unusual signs. These unusual effects are explained by a higher degree of twis t in the deuterio than the protio compound Steric isotope effects are also observed on OH chemical shifts of sterically hindered o-hydroxy a cetyl aromatic compounds deuteriated at the methyl group. These isotop e effects show non-additivity. For one-bond isotope effects, (1) Delta (13)C(O-18), hydrogen bonding leads to a decrease, whereas twisting of the carbonyl group leads to an increase. Two hydrogen bonds to the sa me acceptor has a reduced cumulative effect, Data for sterically hinde red, hydrogen-bonded compounds are found tea fall outside the correlat ion between delta(O-17) and (1) Delta(13)C(O-18).