Naslov
Reactivity of cations and zwitterions formed in photochemical and acid-catalyzed reactions from m-hydroxycycloalkyl substituted phenol derivatives

Autori
Cindro, Nikola ; Antol, Ivana ; Mlinarić-Majerski, Kata ; Halasz, Ivan ; Wan, Peter ; Basarić, Nikola

Izvornik
Journal of organic chemistry (0022-3263) 80 (2015), 24; 12420-12430

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
excited state proton transfer (ESPT) ; carbocations ; zwitterions ; DFT ; laser flash photolysis ; m-quinone methide

Sažetak
Three m-substituted phenol derivatives, each with a labile benzylic alcohol group and bearing either protoadamantyl 4, homoadamantyl 5, or a cyclohexyl group 6, were synthesized and their potential thermal acid-catalyzed and photochemical solvolytic reactivity studied, using preparative irradiations, fluorescence measurements, nanosecond laser flash photolysis, and quantum chemical calculations. The choice of m-hydroxy-substitution was driven by the potential for these phenolic systems to generate m-quinone methides on photolysis which could ultimately drive the excited state pathway, as opposed to forming simple benzylic carbocations in the corresponding thermal route. Indeed, thermal acid-catalyzed reactions gave the corresponding cations which undergo rearrangement and elimination from 4, only elimination from 5, and substitution and elimination from 6. On the other hand, photoexcitation of 4-6 to S1 in a polar protic solvent, proton dissociation from the phenol coupled by elimination of the benzylic OH (as hydroxide ion) gave zwitterions (formal m-quinone methides). The zwitterions exhibit different reactivity from the corresponding cations due to a difference in charge distribution, as shown by DFT calculations. Thus, protoadamantyl zwitterion has a less non-classical character than the corresponding cation so it does not undergo 1, 2-shift of the carbon atom, as observed in the acid-catalyzed reaction.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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