Media type: E-Article Title: A critical evaluation of heteronuclear TOCSY (HEHAHA) experiments for 1H,6Li spin pairs Contributor: Bergander, Klaus; Hüls, Dietmar; Glaser, Steffen J.; Günther, Harald; Luy, Burkhard imprint: Wiley, 2014 Published in: Magnetic Resonance in Chemistry Language: English DOI: 10.1002/mrc.4131 ISSN: 0749-1581; 1097-458X Keywords: General Materials Science ; General Chemistry Origination: Footnote: Description: <jats:p>Heteronuclear TOCSY (HEHAHA) experiments for <jats:sup>1</jats:sup>H,<jats:sup>6</jats:sup>Li spin pairs in organolithium compounds with adjacent strongly coupled <jats:sup>1</jats:sup>H,<jats:sup>1</jats:sup>H spin systems showed unexpected cross peak behaviour: for <jats:italic>n</jats:italic>‐butyllithium <jats:sup>1</jats:sup>H,<jats:sup>6</jats:sup>Li cross peaks were completely missing, whereas for the dimer of (<jats:italic>Z</jats:italic>)‐2‐lithio‐1‐(<jats:italic>o</jats: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 <jats:sup>6</jats:sup>Li,<jats:sup>1</jats:sup>H‐HET‐PLUSH‐TACSY sequence then showed the expected <jats:sup>6</jats:sup>Li,<jats:sup>1</jats:sup>H cross peaks for the transfer via the directly coupled <jats:sup>1</jats:sup>H and <jats:sup>6</jats:sup>Li nuclei. For <jats:italic>n</jats:italic>‐butyllithium transfer to H(C<jats:sub>α</jats:sub>) via an unresolved heteronuclear coupling constant below 0.1 Hz is unambiguously observed. Cross peaks in the 2D <jats:sup>6</jats:sup>Li,<jats:sup>1</jats:sup>H‐HET‐PLUSH‐TACSY spectra for the dimer of (<jats:italic>Z</jats:italic>)‐2‐lithio‐1‐(<jats:italic>o</jats:italic>‐lithiophenyl)ethane are readily explained by the measured coupling network and the corresponding active mixing conditions. Copyright © 2014 John Wiley & Sons, Ltd.</jats:p>