Search

9-13C-Anthrone (1), -9-methylanthracene (2), and -9-methoxyanthracene (3) enriched to more than 90% have been synthesized and carbon-carbon coupling constants involving the labeled-9-carbon have been determined. It is shown that these long-range carbon-carbon couplings can be used to make correct chemical shift assignments. These assignments are verified by a study of homologous compounds and of proton-coupled spectra. These long-range carbon-carbon coupling constants, along with previously obtained couplings from toluene and benzoic acid, find good correlation with the π-bond order of the respective coupling paths. A surprisingly large 4Jcc is noted for 2 and 3.

Fluorene-9-13C, fluorenone-9-13C, acenaphthenone-11-13C, acenaphthenone-12-13C, 1-methylcyclopentanol-1-13C and 1-methylcyclopentene-1-13C were synthesized to obtain J(CC) values between the natural carbons and the labeled carbons. Each of these compounds possessed at least one asymmetric dual-path coupling, i.e., coupling between the labeled carbon and another carbon via simultaneous two- and three-bonded coupling paths. Model 13C-labeled compounds were synthesized where necessary to give expected values of the constituent mono-path couplings. Values of these dual-path couplings (2+3)J suggested that the observed value is the (at least approximate) algebraic sum of the two constituent J values.

In a series of norbornanes, benzonorbornenes, and norbornenes, the vicinal cis couplings 3Jexo,exo and 3Jendo,endo are determined. A trend is recognized in which Jexo,exo steadily decreases in this series while Jendo,endo remains relatively constant; in norbornenes Jexo,exo and Jendo,endo are about the same. These observations are understood by means of theoretical calculations performed for representative compounds of the series. This study indicates that interactions of the C7-methylene bridge with the bonds of the C2C3 ethylene bridge are responsible for the nonequivalence of Jexo,exo and Jendo,endo in norbornanes, and that in norbornenes interaction of the olefin functionality with bonds of the ethylene bridge is responsible for bridging Jexo,exo back fortuitously close to Jendo,endo.

A series of (>90% isotopic purity) 13C-labeled aliphatic alcohols of the general structure CCC13COH were synthesized and studied by 13C n.m.r. to obtain all 13C13C couplings involving the labeled carbon. The 2J(CC) values were small (

A series of 7-13C-labeled o-substituted toluene derivatives and carboxyl-13C-isocrotonic and crotonic acid were synthesized and studied by 13C NMR spectroscopy to obtain 13C13C spin-spin coupling constants involving the labeled carbon. The cis3J(CC) values were different from those in previous studies in that these J(CC) values were relatively small and the usual dependence of 3J(CC) on the s-character of the terminal carbon was reversed. Further, a strong dependence of 3J(CC) on the conformational orientation of a terminal carbonyl group was shown to exist. Through-space interactions of the two coupling carbons were shown to contribute to these ‘anomalous’ results, and thus it was shown the cis carbon-carbon couplings may not be directly related to geometrically equivalent proton-proton couplings, as are other carbon-carbon couplings.