¹⁷O nuclear magnetic resonance spectroscopic study of substituted phthalic anhydrides and phthalides

Abstract

IntroductionThe differential reactivity of the two carbonyl groups of unsymmetrically substituted phthalic anhydrides has been extensively studied (1-9); however, clear understanding of the factors that control the selectivity has yet to be achieved. The utility of 170 nrnr spectroscopy has been rapidly increasing (10-12), and it has been successfully used to estimate electronic characteristics (13-15) and local environment changes arising from steric interactions for a number of functional groups (16-21), including carbonyl groups (1 8-21). For example, it has been recently demonstrated that large bulky groups (e.g., tert-butyl) cause considerable in-plane distortion of the molecular structure of phthalic anhydride when placed at the 3 position (22). The steric interactions were reflected in the 170 chemical shift data of these compounds. In an effort to gain insight into the influence of substituents of varying electronic character on the properties and reactivities of the two carbonyl functions of 3-substituted phthalic anhydrides, we have studied the 170 chemical shifts of a series of phthalic anhydrides (1) and related phthalides (2 and 3).

On the regioselectivity of the condensation of stabilized phosphoylids with 3-substituted phthalic anhydrides

“…Recent experimental results suggest that the 3-nitro substituent in 6 assumes a 0 Po 6 nonplanar conformation. From the study of the "0 chemical shift-torsional angle relationship, it is estimated that the 3-nitro group is rotated 35" from the plane of the aromatic ring (15,16). The MIND013 calculations (17) carried out on the model with nonplanar NO2 show that the LUMO coefficient on the carbon of the ortho carbonyl group is only marginally larger than the LUMO coefficient on the carbon of the meta group 6.…”