The polar bond-polarizable bond interaction in 1-X,2-methoxy naphthalenes.An experimental and theoretical study

In this work, several features of the polar bond-polarizable bond interacti on are studied using an experimental and theoretical methodology. The NMR C -13 chemical shifts for 1-CN,2-OCH3-naphthalene, 1-CHO,2-OCH3-naphthalene a nd 5-CHO,CH3,8-NH2-quinoline were measured. In these three compounds, steri c interactions force the methoxy group to be oriented cis to the adjacent C -C bond with the smaller pi mobile bond order. GIAO DFT-B3LYP/6-311G** magn etic shielding calculations were performed on such compounds, on their corr esponding monosubstituted analogs, and on model systems that intend to mimi c the electrostatic response of a naphthalene substrate to a polar group. E ffects of sigma electron delocalization interactions on the methoxy C-13 ch emical shift are studied separately using the NBO approach. Failure of the level of theory employed to describe some C-13 chemical shifts in the chlor ine-containing compound ore rationalized in terms of contributions from the spin orbit interaction. The model compounds studied in this work shed ligh t on the influence of the double bond character on the PBPzB interaction. A romatic C-13 chemical shifts were proven to be sensitive probes to measure such interaction, which can be thought of as the pi electrostatic response to a proximate polar moiety, causing a shielding effect on the carbon atom nearest to the positive end of the polar group. (C) 2000 Elsevier Science B .V. All rights reserved.