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Low‐Temperature 13 C‐NMR Spectra of 6 Li‐ and 13 C‐Labelled Sulfur‐ and Selenium‐Substituted Organolithium Derivatives
Author(s) -
Seebach Dieter,
Gabriel Josef,
Hässig Robert
Publication year - 1984
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19840670421
Subject(s) - chemistry , heteroatom , geminal , nmr spectra database , selenium , crystallography , tetrahydrofuran , sulfur , coupling constant , delocalized electron , chemical shift , nuclear magnetic resonance spectroscopy , spectral line , stereochemistry , ring (chemistry) , organic chemistry , physics , particle physics , astronomy , solvent
The 13 C‐NMR spectra of 19 different, singly, doubly, and triple 13 C‐labelled α‐sulfur‐ and α‐selenium‐substituted 6 Li‐derivatives generated from methyl and phenyl thioethers, thioacetals, trithio‐orthoesters and from their selenium analogues have been recorded in ethereal solutions (tetrahydrofuran (THF), 2‐methyltetrahydrofuran (MTHF) at temperatures between −30° and −110°. The effects of H/Li‐exchange upon chemical shifts and coupling constants, as well as the values and multiplicities of Li, 13 C‐coupling are interpreted in vie wof crystal structures of some of the same compounds. In two thirds of the cases studied, the H‐decoupled 13 C‐NMR signals observed below −80° were triplets, proving that the C‐atoms are bonded to single 6 Li‐atoms. This is compatible either with monomeric or with dimeric, heteroatom‐bridged structures. The direct 1 H, 13 C‐ and 13 C, 13 C‐coupling constants ( 1 J ) decrease, the 13 C, 77 Se‐coupling constants increase upon lithiation. More striking is that the geminal coupling 13 C‐S‐ 13 C ( 2 J ) is too small to be observed in the non‐metalated species, while it ranges from 3.7 to 7.5 Hz in the lithiated derivatives. These observations may be interpreted as resulting from delocalization of electron density from the carbonionic center towards the adjacent heteroatom.