Abstract: The dependence of the orientation of aryloxydefluorination of 2,4-difluoronitrobenzene (1) (o/p ratio) by the action of X-substituted lithium phenoxides 2 (X = p-OMe, p-Me, p-Et, p-iPr, p-tBu, m-Me, H, p-F) in liquid ammonia in the temperature range from -55 to -35 degreesC has been investigated. The enthalpic preference for ortho-fluorine substitution decreases with weakening substituent electron-donating capability in the order: p-OMe > p-Me approximate to p-Et > m-Me,H greater than or equal to p-E The predominant fluorine substitution at the ortho position for X = p-Me, p-Et turns into a preference for substitution at the para position when X = p-iPr, and this increases further on going to X = p-tBu. PM3, AM1 and MNDO MO calculations showed greater stability of the intermediate anionic sigma -complexes formed on nucleophile addition at the para position, thus suggesting that the predominant ortho substitution manifested for X = p-OMe, m-Me, H, p-F and p-Alk = Me, Et is due to control over orientation by the charge distribution in the substrate. The substrate electronic structure, as a controlling factor, is probably changed by the relative stability of intermediate anionic sigma -complexes on going to p-Alk = iPr, tBu, as a consequence of an enhancement of the substituent's electron-withdrawing nature with the increase in alkyl group polarizability in the order: p-Me approximate to p-Et < p-iPr < p-tBu.

Cite: Politanskaya L. , Malykhin E. , Shteingarts V.
The influence of nucleophile substituents on the orientation in the reaction between 2,3-difluoronitrobenzene and lithium phenoxides in liquid ammonia
European Journal of Organic Chemistry. 2001. V.2001. N2. P.405-411. DOI: 10.1002/1099-0690(200101)2001:2<405::AID-EJOC405>3.0.CO;2-6 WOS Scopus РИНЦ

Dates:

Published print:

Jan 1, 2001

Identifiers:

Web of science	WOS:000166621900022
Scopus	2-s2.0-0035133446
Elibrary	13366730
OpenAlex	W2017605209

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