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Polymers 2010, 2(3), 353-363; doi:10.3390/polym2030353

Diasteromeric Effect on the Homolysis of the C–ON Bond in Alkoxyamines: A DFT Investigation of 1,3-Diphenylbutyl-TEMPO

* ,
UMR 6264 LCP CNRS-Aix-Marseille Université, case 521, Avenue Escadrille Normandie-Niemen, 13397 Marseille Cedex 20 France
* Author to whom correspondence should be addressed.
Received: 2 September 2010 / Revised: 16 September 2010 / Accepted: 16 September 2010 / Published: 27 September 2010
(This article belongs to the Special Issue Advanced Polymer Architectures)
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The rate constants kd of the homolysis of the C–ON bond in styryl dyads TEMPO-based alkoxyamines have recently been published (Li et al. Macromolecules 2006, 39, 9201). The diastereoisomers exhibited different values which were higher than for the unimer TEMPO-styryl alkoxyamine 1. At a first glance, the localization of the steric strain was not obvious. To decipher this problem, diastereoisomer models 2 (RR/SS) and 3 (RS/SR), as well as the released alkyl radicals, were calculated at the \B3LYP/6-31G(d) level. It was revealed that the increase in kd from 1 to 3 was due to the compression (buttressing effect) of the reactive center by the second styryl moiety. The difference in kd for the diastereoisomer was clearly an activation entropy effect DS because the alkyl fragment of the RS/SR diastereoismer exhibited the same conformation as the released radical whereas the conformation for the RR/SS diastereoisomer was quite different and thus required the rotation of several bonds to reach the correct TS, which cost DS, and thus lowers kd.
Keywords: DFT calculations; nitroxide mediated polymerization; remote steric effect DFT calculations; nitroxide mediated polymerization; remote steric effect
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Blachon, A.; Marque, S.R.A.; Roubaud, V.; Siri, D. Diasteromeric Effect on the Homolysis of the C–ON Bond in Alkoxyamines: A DFT Investigation of 1,3-Diphenylbutyl-TEMPO. Polymers 2010, 2, 353-363.

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