No abstract

No abstract

Carbon-13 n.m.r. data have been determined for a series of 26 aromatic carbony4 compounds inciuding benzoyl, naphthoyl and pyrenoyl derivatives 13C labelled in the carbonyl group. Doubly labelled anthraquinone has also been included. The compounds investigated comprise non-hindered molecules and molecules in which the carbony1 substituent is subject to orthoor periinteractions affecting conjugation of the carbonyl group with the aromatic ring. The dependence of long range 13C,13t couplimg constants involving the carbonyl carbon, in particular ' J and "J, on steric conditions is discussed, as is the possibility of deciding on the orientation of the carbonyl bond. The following results have emerged. zJ(s-t)>zJ(s-c) for ketones and aldehydes, and the reverse is valid for acids and acid derivatives. (s-t and s-c refer to the orientation of the -0 group relative to the aromatic bond in question with respect to the connecting single bond). For ketones "J(t,~-c)<~J(f,s-t), and both of these "J(t) values decrease with increasing angle of twist, 8, about the single bond, whereas 3J(c,s-c) increases with 8. For acids and acid derivatives no shnilar regularity was found.(The initial f and c refer to the geometry of the three-bond coupling path). Generally it is found that "J( t ) > 3J(c) and 'J( r) > 'J, confirming earlier results. Theoretical calculations on a few model compounds are qualitatively in accordance With the experimental results. Some sign determinations for coupling constants are presented. A short discussion is given of substituent effects on chemical shifts. Observed trends are consistent with earlier results. nation of dipole moment^,^'^ 13C n.m.r. chemical shifts5-' and molar Kerr constants' have been applied. Also X-ray methods have been used." In the present work two-and three-bond coupling constants "J(C0,Ci) are discussed in connection with this problem. The observed coupling constants have also been compared with theoretical values corresponding to

No abstract

No abstract

No abstract

No abstract

No abstract