Long‐range ¹H coupling interactions: Identification of different pathways by 2D NMR δ—δ correlated spectroscopy. Applications in structural analysis

Abstract

The simplest methods of 2D 6-6 correlated spectroscopy (COSY and COSY LR) allow the easy observation of long-range coupling interactions. It is shown how these methods can lead to the discrimination between different pathways across single bonds: 4J through coplanar or gauche arrangement of the bonds and ' J through a zig-zag pathway or bond proximity. Applications to configurational and conformational analysis of polycyclic compounds, a trimer of isophorone, two natural terpenoids (carotol and daucol) and four steroids, are presented.KEY WORDS 2D NMR correlated spectroscopy COSY COSY LR Long-range couplings Coupling pathways.

Using indirect covariance processing for structure elucidation of small molecules in cases of spectral crowding

“…The observation of long‐range couplings has extensively been discussed in the literature. With respect to this study, cf Refs 27–30.…”

“…Besides the higher sensitivity, multistep or RCOSY responses have been suggested as explanation as well for the appearance of more correlations 19, 24. Since the observation of long‐range couplings due to mechanisms such as W‐ and zig‐zag28 in COSY‐type spectra is rather common for steroids, it is not obvious how to differentiate between multistep correlations and other mechanisms in covariance processed spectra. The number of artifacts other than multistep responses that were observed in the computed spectra was found to be relatively small, as supported by the numbers given in Table 1.…”

Fe(CO)3 and Rh(acac) complexes of ergosteryl and 7-dehydrocholesteryl acetates: A high field nuclear magnetic resonance study

“…Since this initial paper, detection and treatment of breast cancer. numerous other reports of the 'H spectra of steroids have this paper, we the l H and I~C NMR spectra for appeared in the literature (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16) In contrasty the 13' NMR 3p-acetoxyergosta-5,7,22 triene (ergosteryl acetate), 1, and for spectra of steroids have been exhaustively studied and excellent the closely related steroid, 3P-acetoxycholesta-5 ,7 diene (7compilations are now available (1 7, 1 8). dehydrocholesteryl acetate), 2; we also present the spectra of Another aspect Of steroid which has gained promtheir Fe(C0)3 and Rh(acac) derivatives 3 through 6.…”

“…As pointed out by others (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)30), it is still not trivial to assign all the proton resonances in complex steroids even taking advantage of the full armamentarium of 2D techniques currently available. Since there are over 40 protons in each of the compounds and the 13C NMR spectra of the 3P-acetate esters of ergosterol and of 7-dehydrocholesterol were already known (17, 31), the initial phase of our investigation involved the measurement of heteronuclear 'H-I3c shift correlated spectra (32).…”

Staudtienic Acid, a Diterpene Acid from Staudtia kamerunensis

“…Structure 1 was confirmed by observation of long range couplings in the : -*H long range COSY between the aromatic H-12 and methylene H-15 and between the aromatic H-14 and both methylenes H-7 and H-15. A cross peak observed between Me-20 and H-lax indicated that they were in a trans-diaxial relative disposition (2). Assignment of the ethylenic methylene protons at C-17 arose from the values of their 3/H-h coupling constant with H-16, which was 16.9 Hz for H-17Z and 9.9 Hz for H-17E.…”