A critical evaluation of heteronuclear TOCSY (HEHAHA) experiments for 1H, 6Li spin pairs1. (28th August 2014)

• Record Type: Journal Article
• Authors: Bergander, Klaus; Hüls, Dietmar; Glaser, Steffen J.; Günther, Harald; Luy, Burkhard
• Is Part Of: Magnetic resonance in chemistry. Volume 52:Number 12(2014:Dec.)
• Page Start: 739
• Page End: 744
• Publication Date: 2014-08-28
• Subjects: Nuclear magnetic resonance spectroscopy -- Periodicals; Chemistry, Organic -- Periodicals; Magnetic resonance -- Periodicals; 538.36
• DOI: 10.1002/mrc.4131
• Languages: English
• ISSNs: 0749-1581

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Heteronuclear TOCSY (HEHAHA) experiments for ¹H, ⁶Li spin pairs in organolithium compounds with adjacent strongly coupled ¹H, ¹H spin systems showed unexpected cross peak behaviour: for <italic>n</italic>‐butyllithium ¹H, ⁶Li cross peaks were completely missing, whereas for the dimer of (<italic>Z</italic>)‐2‐lithio‐1‐(<italic>o</italic>‐lithiophenyl)ethane, a cross peak for remote protons was observed even at very short mixing times. It was assumed that strong magnetization transfer within the proton spin systems was responsible for these results, which prevented unambiguous chemical shift assignments. Selective experiments with the ⁶Li, ¹H‐HET‐PLUSH‐TACSY sequence then showed the expected ⁶Li, ¹H cross peaks for the transfer via the directly coupled ¹H and ⁶Li nuclei. For <italic>n</italic>‐butyllithium transfer to H(C_α) via an unresolved heteronuclear coupling constant below 0.1 Hz is unambiguously observed. Cross peaks in the 2D ⁶Li, ¹H‐HET‐PLUSH‐TACSY spectra for the dimer of (<italic>Z</italic>)‐2‐lithio‐1‐(<italic>o</italic>‐lithiophenyl)ethane are readily explained by the measured coupling network and the corresponding active mixing conditions. Copyright © 2014 John Wiley &amp; Sons, Ltd.</p> </abstract>