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The shielding of H‐α in the stabilized rotameric forms of α,α‐di‐ tert ‐butylthioacetic esters. The electric and magnetic anisotropic effects of the thione group
Author(s) -
Balasubrahmanyam S. N.,
Bharathi S. Narasimha,
Usha G.
Publication year - 1983
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/omr.1270210805
Subject(s) - anisotropy , chemistry , electromagnetic shielding , spectral line , group (periodic table) , chemical shift , branching (polymer chemistry) , shielding effect , crystallography , cndo/2 , alkane stereochemistry , stereochemistry , nuclear magnetic resonance , physics , molecule , organic chemistry , crystal structure , quantum mechanics
The currently accepted geometry of carbonyl magnetic anisotropic effects, if regarded as extendable to the thione group, imply that the more deshielded of the two H‐α lines in the 1 H NMR spectra of α,α‐di‐ tert ‐butylthioacetic esters should be assigned to the ‘180° form’ in which CS is antiperiplanar to C‐αH. CNDO results, however, indicate the opposite; the line should be assigned to the ‘O° form,’ in which CS eclipses C‐αH, if the predicted considerable increase in 1s density at H‐α on going from the 0° form to the 180° form is taken into account. A change in 1s density at H‐α as a result of increased branching of alkylation at C‐α is also found. These specific effects must be taken into account when discussing the anisotropic effects of CO or CS on H‐α shifts.