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Reaction selectivity, hydrogen isotope effect and steric hindrance in the aromatic halogenation of polyalkylbenzenes

✍ Scribed by Enrico Baciocchi; Gabriello Illuminati; Giancarlo Sleiter

Publisher: Elsevier Science
Year: 1960
Tongue: French
Weight: 267 KB
Volume: 1
Category: Article
ISSN: 0040-4039
DOI: 10.1016/s0040-4039(00)70276-0

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✦ Synopsis

The observation that aromatio halogenation with moleoular halogen ie a lees eeleotive reaotion with polymetbylbeneenee then with monosubatituted benzenee, a~ based on the reaotion con&ante of the reaotione in eaoh individual eerie6 2,3 , aaggests that the two methyl group8 ortho to the attaoked position in the former moleoules may effeotively lower the eensitivity of the reagent to the ohanges of the eleotron density of the aromatio'eubetrate by hindering the approach of the attaoking entity. Presumably a sterio effeot of this kind may alter the detailed timing of the prooees and be accrompanied by a shift of the reaotion ooordinate for the rate-determining transition state toward increasing extents of C-E bond breaking, in the potential energy ourve of the reaotion. If bond breaking made enough progreee, a hydrogen isotope effeat would result in the aromatic halogenation of hindered polymethylbenzenee.

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