In:
Magnetic Resonance in Chemistry, Wiley, Vol. 42, No. 9 ( 2004-09), p. 776-780
Abstract:
It is demonstrated that long‐range n J ( 1 H, 117 Sn) coupling constants down to 0.3 Hz, can be accurately quantified from non‐linear fitting of the sine modulation of the associated 1 H 117 Sn correlation cross‐peak intensities sampled as a function of the heteronuclear antiphase coherence preparation time in the 1 H 117 Sn J ‐HMQC pulse sequence. The contribution of additional, undesired modulations is illustrated and assessed using the product operator formalism, and is traced back to contributions that arise from miss‐setting of the wandering 180° pulse angle in the constant time period. The power of the method and its use in the characterization of weak intramolecular donor–acceptor interactions are illustrated by the determination of long‐range n J ( 1 H, 117 Sn) coupling constants of bis[3‐(dimethylamino)propyl]tin derivatives, [Me 2 N(CH 2 ) 3 ] 2 SnR 2 ( 2 , R = Me; 3 , R = Ph; 4 , R = t ‐Bu). By comparing these with the values found for the corresponding bis(4‐methylpentyl)tin derivatives, [Me 2 CH(CH 2 ) 3 ] 2 SnR 2 ( 2 ′ , R = Me; 3 ′ , R = Ph), which lack such interactions, the use of long‐range coupling constants to detect intramolecular donor–acceptor interactions is evaluated. It is concluded that n J ( 1 H, 117 Sn) couplings up to six bonds through an organic carbon chain can be quantified, whether donor–acceptor interactions are present or not. Furthermore, evidence is presented that, when two scalar coupling pathways co‐exist, the pathway involving an intramolecular donor–acceptor interaction can have opposite sign, thus decreasing the overall coupling constant to a value smaller than that actually measured in the absence of a donor–acceptor interaction, where only one coupling pathway is active. There is nevertheless clear numerical value discrimination in the series of compounds investigated between long‐range couplings in derivatives without weak intramolecular donor–acceptor interactions and those where such interactions can exist. Copyright © 2004 John Wiley & Sons, Ltd.
Type of Medium:
Online Resource
ISSN:
0749-1581
,
1097-458X
Language:
English
Publisher:
Wiley
Publication Date:
2004
detail.hit.zdb_id:
1475029-6
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