The Electrophilic Substitution of Arenes: Is the π Complex a Key Intermediate and What Is Its Nature?

Lenoir, Dieter

doi:10.1002/chin.200319226

Cited by 1 publication

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“…[2][3][4] For example, the electrophilic aromatic substitution reaction of benzene (C6H6) proceeds via C6H6 + E + ⇄ [C6H6E] + → C6H5E + H + , in which E + is an electrophile; [C6H6E] + can be regarded as a protonated substituted benzene. [5][6] The preferred site of protonation in the substituted benzenes and the energetics of protonation are thus important in determining the rate of such chemical reactions. The physical conditions (e.g., temperature and pressure), the substitution by functional groups, and solvation might affect the preferential site of protonation.…”

Section: Introductionmentioning

confidence: 99%

Infrared Spectra of Isomers of Protonated Aniline in Solid para-Hydrogen

2020

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The protonation sites of aniline molecule play important roles in its chemical reactions, but the preferred protonation site of gaseous aniline has yet to be determined. In this work, we recorded infrared (IR) absorption spectra of three isomers of protonated aniline, H + C6H5NH2, produced on electron bombardment during matrix deposition at 3.2 K of a mixture of aniline and para-H2. The intensities of IR lines of H + C6H5NH2 decreased during maintenance of the electron-bombarded matrix in darkness because of neutralization with electrons that were slowly released from their trapping sites. The observed lines were classified into three groups according to their behavior upon secondary photolysis with light at 375 and 254 nm and assigned to para-, amino-, and ortho-H + C6H5NH2, the three most stable isomers of protonated aniline, according to comparison of experimental spectra with quantumchemically predicted spectra of five possible isomers of H + C6H5NH2. The spectra of para-and ortho-H + C6H5NH2 are newly distinguished. The approximate relative abundance of these isomers in solid p-H2 was para : amino : ortho ≈ (1.0 ± 0.1) : (1.0 ± 0.6) : (0.6 ± 0.1). The possible mechanisms of formation are discussed.

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