Details

Autor(en) / Beteiligte

• Politanskaya, Larisa
• Malykhin, Evgenij
• Shteingarts, Vitalij

Titel

The Influence of Nucleophile Substituents on the Orientation in the Reaction between 2,4-Difluoronitrobenzene and Lithium Phenoxides in Liquid Ammonia

Ist Teil von

• European journal of organic chemistry, 2001-01, Vol.2001 (2), p.405-411

Ort / Verlag

Weinheim: WILEY-VCH Verlag GmbH

Erscheinungsjahr

2001

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• 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 °C has been investigated. The enthalpic preference for ortho‐fluorine substitution decreases with weakening substituent electron‐donating capability in the order: p‐OMe > p‐Me ≈︁ p‐Et > m‐Me > H ⩾ p‐F. 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 σ‐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 σ‐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 ≈︁ p‐Et < p‐iPr < p‐tBu.