Abstract
A rigorous error analysis of LIS is described which avoids the use of any normalising atom. This analysis is used to investigate the LIS of benzaldehyde and thiophen- and furan-2-aldehyde. The non pseudo-contact components of the Yb(fod) 3 induced shifts are isolated and found to be appreciable at the carbonyl carbon and the ortho and para carbons. Estimation of the diamagnetic contribution to these shifts with La(fod) 3 allows a precise analysis of the 1H and 13C LiS of these aldehydes without the need to invoke any contact shifts. The lanthanide-complex geometry found is essentially one-site, i.e. 100% population on the unhindered exo side of the carbonyl. The lanthanide is in the molecular plane of the aldehydes with Ln O and Ln.O.C. parameters of ca 2.5A˚and 140°, respectively. This procedure also gives the percent population of the O-cis conformer of furfural as ca 70–75% in CDCl 3 solution.
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