March 11- 16, 2001. Orlando, Florida, USA, 42nd ENC

J-Coupler - A Tool for Automated First Order Multiplet Analysis

Antony Williams, Sergey Golotvin, Eugene Vodopianov

Abstract

We are all well aware that the dependence of the values of NMR spin-spin coupling constants on molecular conformation can be a valuable tool in the structure determination process. The continuing increase in the resonance frequency of modern NMR spectrometers allows more and more resonances to be examined using first-order multiplet analysis. While this can easily be done for the simplest patterns (doublets, triplets, quartets), more complex patterns can be extremely difficult to analyze. This is certainly an issue for synthetic organic chemists accessing walk-up spectrometers and who have not received the appropriate training in spectral analysis. The task of deducing the coupling constant values from a multiplet is the reverse process of generating a conventional splitting tree from a single line (chemical shift) by sequential branching using a given set of coupling constants. Although the general protocol of inverted splitting tree generation was published several years ago, it does not seem to have found widespread use. We will present a simple straightforward method of deducing coupling constant values from first-order multiplets based on a general inverted splitting tree algorithm but also including a peak intensity normalization procedure that utilizes multiplet symmetry and generates a set of possible first-order intensity distribution patterns. When combined together with a inverted splitting tree algorithm it is possible to find an intensity pattern that allows deduction of a proper set of coupling constants.

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