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The spin delocalization substituent parameters σ: 3. The spin‐delocalizing abilities of the acetyl and trimethylsilyl groups. Synthesis of four substituted trifluorostyrenes
Author(s) -
YuHuang Zhang,
DaXin Wang,
GuoZhen Ji,
XiKui Jiang
Publication year - 1988
Publication title -
acta chimica sinica english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.28
H-Index - 41
eISSN - 1614-7065
pISSN - 0256-7660
DOI - 10.1002/cjoc.19880060212
Subject(s) - chemistry , trimethylsilyl , substituent , ethylene , chemical shift , medicinal chemistry , delocalized electron , polar effect , spin (aerodynamics) , electron delocalization , stereochemistry , computational chemistry , organic chemistry , catalysis , thermodynamics , physics
Four substituted α, β, β‐trifluorostyrenes (TFSs) namely, p trimethylsilyltrifluorostyrene (1), p ‐acetyltrifluorostyrene ethylene ketal (2), p ‐acetyltrifluorostyrene (3) and p ‐phenoxytrifluorostyrene (4), have been synthesized. The rate constants ( k 2 ) of the thermal cyclodimerization of 1 and 3 have been measured in the temperature range 120—160°C. The polar parameters σ P of the four TFSs calculated from 19 F NMR chemical shifts are: for p ‐trimethylsilyl‐1, 0.21; 1‐ethylenedioxy‐ethyl‐, —0.01; p ‐acetyl‐, 0.61 and p ‐phenoxy‐,—0.47. The spin de‐localization substituent parameters σ• T of p ‐trimethylsilyl and p ‐acetyl groups are 0.29 and 0.52 respectively. Thus both the p ‐trimethylsilyl and the p ‐acetyl groups act as electron‐attracting groups which can also effectively stabilize a spin.