Conformationally controlled intramolecular charge transfer complexes

Daniel Kost, Na'Ama Peor, Gali Sod-Moriah, Yifat Sharabi, David T. Durocher, Morton Raban

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Trans-1-acceptor-2-donor-substituted cyclohexanes (1), as well as their 4- (or 5-)methyl-substituted homologues (2), have been prepared and are shown to form intramolecular charge-transfer (donor-acceptor) complexes. These weak complexes are turned on and off by the chair-chair interconversion of the cyclohexane ring. The CT absorptions have been measured and the equilibrium constants for the ring reversal have been determined by UV/vis spectroscopy at 298 K, as well as by NMR spectroscopy at two temperatures: at 183 K, by direct comparison of signals due to the two chair conformations, and at 300 K, by comparison of calculated and measured widths of the α-proton signals. The Gibbs free energies assigned to the donor-acceptor interactions range between 0 and -1 kcal mol-1. A crystal structure of one of the complexes (1b) confirms the intramolecular donor-acceptor alignment and interaction. The regioisomers of the methyl-substituted complexes were characterized by NOE interaction between the methyl and an α-proton cis to it.

Original languageEnglish
Pages (from-to)6938-6943
Number of pages6
JournalJournal of Organic Chemistry
Issue number20
StatePublished - 4 Oct 2002

ASJC Scopus subject areas

  • Organic Chemistry

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