首页   按分类浏览 期刊浏览 卷期浏览 An NMR Study of intramolecular shielding in AlkylN(Arylsulfonyl)Methyl]‐Carbamates, ‐Th...
An NMR Study of intramolecular shielding in AlkylN(Arylsulfonyl)Methyl]‐Carbamates, ‐Thiolcarbamates, ‐Thionocarbamates, and ‐Dithiocarbamates

 

作者: S. van der Werf,   J. B. F. N. Engberts,  

 

期刊: Recueil des Travaux Chimiques des Pays‐Bas  (WILEY Available online 1970)
卷期: Volume 89, issue 4  

页码: 423-441

 

ISSN:0165-0513

 

年代: 1970

 

DOI:10.1002/recl.19700890413

 

出版商: WILEY‐VCH Verlag

 

数据来源: WILEY

 

摘要:

AbstractThe chemical shifts of the ester alkyl groups of alkylN‐[(arylsulfonyl)methyl]‐carbamates are displayed as doublets of unequal intensity at temperatures where rotation around the nitrogen to carbonyl bond is slow on the NMR time scale.Comparison with NMR data of simple alkylN‐substituted carbamates indicates that the ester alkyl absorption of at least one of the rotamers shows an appreciable upfield shift. These upfield shifts are dependent on the ring current in the aromatic nucleus of the molecule. An explanation for these observations is presented in terms of preferred conformations (with minimized lone pair‐lone pair repulsion) in which the ester alkyl group is situated above (or below) the plane of the aromatic ring. Minor structural changes in the molecule eliminate the shielding effect which supports the proposed shielding mechanism. Further evidence for intramolecular shielding was obtained from the observed solvent and temperature dependence of the chemical shifts of the ester alkyl protons. No evidence could be obtained for inter‐ or intramolecular association between the aromatic ring and the ester function.Chemical shift data for alkylN‐[(arylsulfonyl)methyl]thiolcarbamates, ‐thionocarbamates and ‐dithiocarbamates also indicate intramolecular shielding of the este

 

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