Distinguishing between two- and three-bond correlations for all ¹³C multiplicities in heteronuclear NMR spectroscopy

Abstract

A novel two-dimensional method, SEA XLOC, for distinguishing between two- and three-bond correlations in heteronuclear NMR spectroscopy is introduced and demonstrated on ibuprofen and by a complete set of correlations with a simple and most complex quaternary 13C multiplet in strychnine.

Resolution Enhancement in SEA XLOC for Heteronuclear NMR Long‐Range Correlation

“…In a recent report, a two‐dimensional method, SEA XLOC, was introduced for distinguishing between two‐ and three‐bond heteronuclear long‐range correlations in NMR spectroscopy. The distinction is based on different multiplet widths of zero‐quantum (ZQ or echo) and double‐quantum (2Q or antiecho) signals in the indirect dimension of a 2D spectrum of e. g. a 1 H− 13 C correlation one.…”

“…In order to compare the experiment in Figure with the earlier SEA XLOC pulse sequence it must be kept in mind that the former for a given phase cycle requires twice as many scans per t 1 increment as the latter. Thus for the same instrument time the choice is between running the experiment in Figure with a given set of parameters or the earlier version with the same parameters and twice the number of t 1 increments.…”

“…In the limit of high resolution, there is no benefit from doubling the number of t 1 increments in the earlier implementation of SEA XLOC compared to the version in Figure that therefore is expected to offer the best spectral resolution in that regime. In the limit of coarse resolution with double number of t 1 increments in the earlier implementation of SEA XLOC the line widths of and above in principle become and indicating similar resolution in the two alternative implementations.…”

“…Figures and show excerpts of SEA XLOC spectra of ibuprofen (left in Scheme ) obtained with the earlier SEA XLOC pulse sequence (referred to as F 1 ‐magnitude ) and with the new experiment in Figure (referred to as F 1 ‐absorptive ).…”

“…The results are in accordance with the general remarks above. As described in the original paper, the ZQ profile (red) being narrower than the 2Q profile (black) is indicative of a two‐bond correlation and the opposite is indicative of a three‐bond correlation.…”