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Structure elucidation with lanthanide-induced shifts. 4—Bound shifts vs relative shifts

✍ Scribed by Douglas J. Raber; Milton D. Johnston Jr; Catherine M. Campbell; Christopher M. Janks; Pamela Sutton

Publisher
John Wiley and Sons
Year
1978
Tongue
English
Weight
649 KB
Volume
11
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

The use of lanthanide shift reagents (LSR's) to obtain additional structural information from nuclear magnetic resonance studies has gained widespread acceptance. However, there has not been general agreement with regard to the most appropriate methodology for analysis of the shifted NMR spectra. We present arguments that only the bound shifts (Δ~1~) corresponding to the LS complex should be used for correlation of lanthanide‐induced shifts with molecular structure by means of the pseudocontact equation. Several examples are discussed of compounds for which the relative induced shifts are dependent on the concentration of LSR. For such cases it is not possible for both Δ~1~ and Δ~2~ (the bound shift corresponding to the LS~2~ complex) to correlate successfully with the correct structure. Alternative methods of obtaining bound shifts are critically evaluated.

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