| Popis: |
In this work, several features of the polar bond–polarizable bond interaction are studied using an experimental and theoretical methodology. The NMR 13C chemical shifts for 1-CN,2-OCH3-naphthalene, 1-CHO,2-OCH3-naphthalene and 5-Cl,6-OCH3,8-NH2-quinoline were measured. In these three compounds, steric interactions force the methoxy group to be oriented cis to the adjacent C–C bond with the smaller π mobile bond order. GIAO DFT-B3LYP/6-311G∗∗ magnetic shielding calculations were performed on such compounds, on their corresponding monosubstituted analogs, and on model systems that intend to mimic the electrostatic response of a naphthalene substrate to a polar group. Effects of σ electron delocalization interactions on the methoxy 13C chemical shift are studied separately using the NBO approach. Failure of the level of theory employed to describe some 13C chemical shifts in the chlorine-containing compound are rationalized in terms of contributions from the spin orbit interaction. The model compounds studied in this work shed light on the influence of the double bond character on the PB–PzB interaction. Aromatic 13C chemical shifts were proven to be sensitive probes to measure such interaction, which can be thought of as the π electrostatic response to a proximate polar moiety, causing a shielding effect on the carbon atom nearest to the positive end of the polar group. |
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