¹³C, ¹³C coupling constants and ¹³C chemical shifts of aromatic carbonyl compounds. Effects of ortho‐ and peri‐interactions involving the carbonyl substituent

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

On the unusual2Jcoupling dependence onsyn/antiCHO conformation in 5‐X‐furan‐2‐carboxaldehydes

“…[24] Other examples were given by Hansen et al [25,26] who observed that in aromatic aldehydes and ketones the following relationship holds 2 J C C -C s−trans > 2 J C C -C s−cis .…”

Long range 13C13C coupling constants. A review

“…It has been suggested that these signs will be valid in all compounds of this type. 34 Methyl substitution has been found to have little effect on 'J(C0, C-i)34 (Table 12).…”

“…In the original paper on these couplings, Ihrig et aLZ1 noticed a decrease in 2J and an increase in 3J in going from an sp3 to an sp2 hybridized a-carbon but this can no longer be taken as a general rule. 34 In compounds with free rotation around C-1,C-a the ranges of numerical magnitudes were as follows: '5, 1.8-3.98 Hz; 3J, 3.42-5.4 Hz and "J, 0.8-1.18 (Table 11).…”

“…The dependence on the dihedral angle, @, is thus similar to the curve for 3J(FF).31*32 The displacements are probably due to the effect of impinging rear lobes (IRL) and to the dependence on two dihedral angles, and 0 (6), the latter associated with a reorientation of the carboxylic ccid group. 33 The dependence of 3J(cis) on 0 has been studied by Hansen et al 34 who observed an increase in 3J(cis) with increasing 0 (see 25). This means that the Karplu.…”

Azo pigments and their intermediates. A reinvestigation of the tetrazotization of 1,4-diaminoanthraquinone

“…'Comparison of the I3c data of a large number of monosubstituted anthraquinones (at C-1) and disubstituted anthraquinones (at C-1 and C-4) (14, 17) with those of anthraquinone (18) suggests that substituents at carbons 1 and 4 exert very little influence on the chemical shifts of the carbons in the second benzene ring.…”