Carbon‐13 NMR studies of substituted naphthalenes. I—complete assignments of the ¹³C chemical shifts with the aid of deuterated derivatives

Abstract

Proton-coupled as well as noise-decoupled '"C NMR spectra of several substituted naphthalenes have been studied. Complete assignments of the ' " C signals based on selectively deuterated derivatives and on the '"C-'H coupling pattern have been made. For the methoxynaphthalenes, acetylnaphthalenes and naphthaldehydes the dominant conformations of the substituents have been deduced from the '"C chemical shifts.

Naphthalene Glycosides in Cassia senna and Cassia angustifolia

“…undergo a relative downfield shift of + 10, + 5 and + 5 ppm, respectively. This effect parallels the downfield shift already observed for proton H4 (A 6: + 0.3 ppm) confirming that the conjugative interaction of the 1methoxyl group with the naphthalene ring is lost [5].…”

“…The other sugar carbons are almost identical in the five compounds and correspond closely to the shift values reported for f3-glucosyl-coumarines [6]. The methoxyl carbons in anisole and methoxynaphthalene derivatives are known to display a significant downfield shift by increased ortho substitution [5,7]. In TMS ethers were prepared by reaction of the glyeosides and aglycones with a mixture of hexamethyldisilazane and trimethylehiorosilane in pyridine (Tri-sil, Pierce Chemical Company, Rockford, Illinois) for 30 mm at room temperature.…”

“…A detailed analysis of the '3C data shows that their difference resides most probably in the position of the O-(3-glucose substituent. In the five products, three aromatic carbons C,, C6 and C8 substituted by the hydroxyl, methoxyl or glucosyloxy groups are strongly deshielded (6 150 to 159 ppm) with respect to the '3C chemical shift in naphthalene itself [5]. In Ia, lila and V, five carbons C2, C4, Gsa, C5 and C7 are shielded to various amounts by the mesomere effect of the OR substituents in ortho or para positions.…”

“…In these products, proton H4 is shifted downfield by about 0.3 ppm. This may be rationalized by admitting that the more voluminous methoxyl groups, replacing the OH substituent in position 1, is out of plane for steric reasons and cannot longer influence proton H4 by conjugative interaction [5]. This implies the presence of, in addition to the 2-acetyl substituent already mentioned, another substituent in pen position 8.…”

High‐resolution 13C nuclear magnetic resonance spectra of some solid biphenyl derivatives

“…When the aldehydic proton is replaced by a methyl group, this difference is considerably reduced by the effects of steric interaction, as reported for the formyl and acetyl derivatives of naphthalene in solution. 28 The chemical shift assignments in Table 2 for 4,4'-diacetylbiphenyl, therefore, correspond to the following conformation:…”