Convenient criterion for the distinction between electrophilic and electron transfer reactions of electron-rich alkenes

✍ Scribed by Nathan L. Bauld; J. Todd Aplin; Wang Yueh; Stephanie Endo; Angie Loving

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 205 KB
• Volume: 11
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199801)11:1<15::aid-poc960>3.0.co;2-l

✦ Synopsis

Both experimental and theoretical studies confirm that the formation of aryl vinyl ether and aryl vinyl sulfide cation radicals from the corresponding neutral substrates correlates with the Brown ' parameters as opposed to Hammett ' values. Peak oxidation potentials for both classes of substrates correlate preferentially with ' , as do gas-phase ionization energies calculated by both semi-empirical and ab initio methods. In contrast, the protonation energies of the same substrates, which relate to carbocation formation, correlate preferentially with ' values, as do rates of protonation and other electrophilic additions. These observations permit a sharp distinction between electrophilic and electron transfer reactions of these two common classes of electron-rich substrates. Using this criterion, the cycloadditions of tetracyanoethylene to these substrates are found to proceed via an electrophilic mechanism, rather than by a previously proposed electron transfer mechanism.