Protonation and ring closure of stereoisomeric α-substituted cinnamic acids in superacidic media studied by 13C NMR spectroscopy and computations

I. Pálinkó, Arwed Burrichter, Golam Rasul, Béla Török, G. K Surya Prakash, George A. Olah

Research output: Contribution to journalArticle

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Abstract

Five α-substituted cinnamic acids [(E)- and (Z)-2,3-diphenyl-, (E)- and (Z)-3-(2-methoxyphenyI)-2-phenyl- and (E)-2-(2-methoxyphenyl)-3-phenyl-propenoic acids] have been protonated in fluorosulfonic acid at -78°C. Protonation of the carboxylic group and a second protonation on the methoxy group at -78°C or the ring bearing the methoxy group at 0°C have been observed by 13C NMR spectroscopy. Upon protonation (Z)-α-phenylcinnamic acid is transformed to a protonated indenol derivative. Dehydrative ring closure begins at -78°C and goes to completion at 0°C. Similar transformations of the other studied Z-acid are suppressed by the deactivating effect of the protonated methoxy group. Only protonation has been observed for the E-acids at -78°C as well as 0°lculations at the HF/3-21G level provide the equilibrium structures of the corresponding cations. Results of IGLO/13C NMR shift calculations are in good agreement with the experimental findings.

Original languageEnglish
Pages (from-to)379-385
Number of pages7
JournalJournal of the Chemical Society, Perkin Transactions 2
Issue number2
Publication statusPublished - Feb 1998

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Protonation
Nuclear magnetic resonance spectroscopy
Acids
Bearings (structural)
Cations
Nuclear magnetic resonance
Derivatives
cinnamic acid

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Protonation and ring closure of stereoisomeric α-substituted cinnamic acids in superacidic media studied by 13C NMR spectroscopy and computations. / Pálinkó, I.; Burrichter, Arwed; Rasul, Golam; Török, Béla; Prakash, G. K Surya; Olah, George A.

In: Journal of the Chemical Society, Perkin Transactions 2, No. 2, 02.1998, p. 379-385.

Research output: Contribution to journalArticle

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AU - Török, Béla

AU - Prakash, G. K Surya

AU - Olah, George A.

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