Nondegenerate equilibrium in (2-propyl)cycloalkyl cations. Comparison of (2-propyl)cyclopentyl and (2-propyl)cyclohexyl cation using 13C NMR spectroscopy, equilibrium isotope effects and quantum chemical calculations

Hans-Ullrich Siehl; Valerije Vrek; Olga Kronja

doi:10.1039/B107756B

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Nondegenerate equilibrium in (2-propyl)cycloalkyl cations. Comparison of (2-propyl)cyclopentyl and (2-propyl)cyclohexyl cation using ¹³C NMR spectroscopy, equilibrium isotope effects and quantum chemical calculations†

Hans-Ullrich Siehl,*^a Valerije Vr [c with combining breve]

ek^b and Olga Kronja*^b

Author affiliations

* Corresponding authors

^a Division of Organic Chemistry I, University of Ulm, Ulm, Germany
E-mail: ullrich.siehl@chemie.uni-ulm.de
Fax: +49-(0)731 50 22787
Tel: +49-(0)731-5022800

^b Faculty of Pharmacy and Biochemistry, University of Zagreb, Zagreb, Croatia
E-mail: kronja@pharma.hr
Fax: +385-1-485216
Tel: +385-1-4818301

Abstract

Tertiary (2-propyl)cyclopentyl and (2-propyl)cyclohexyl carbocations were investigated by ¹³C NMR spectroscopy in superacid solution. Both ions undergo fast nondegenerate 1,2-hydride shifts to the corresponding 2-cycloalkyl-2-propyl cations. The direction of these equilibria depends on the size of the ring. The more stable isomer of the (2-propyl)cyclopentyl cation has the formal positive charge at the endocyclic carbon atom, while the more stable isomer of the (2-propyl)cyclohexyl cation has the formal charge at the exocyclic carbon atom. The dynamic NMR results were confirmed by NMR spectroscopic measurement of the equilibrium isotope effects and rationalized by quantum chemical calculations.

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Supplementary files

Redundant coordinates for structures 1A, 1B, 1TS, 2A, 2B1, 2B2 and 2TS; van't Hoff plot for equilibrium between 1A and 1B PDF (47K)

Article information

DOI: https://doi.org/10.1039/B107756B
Article type: Paper
Submitted: 28 Aug 2001
Accepted: 29 Oct 2001
First published: 03 Dec 2001

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J. Chem. Soc., Perkin Trans. 2, 2002, 106-113

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Nondegenerate equilibrium in (2-propyl)cycloalkyl cations. Comparison of (2-propyl)cyclopentyl and (2-propyl)cyclohexyl cation using ¹³C NMR spectroscopy, equilibrium isotope effects and quantum chemical calculations

H. Siehl, V. Vr<img border="0" src="https://www.rsc.org/images/entities/char_0063_0306.gif" alt="[c with combining breve]" xmlns="http://www.rsc.org/schema/rscart38" />ek and O. Kronja, J. Chem. Soc., Perkin Trans. 2, 2002, 106 DOI: 10.1039/B107756B

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Journal of the Chemical Society, Perkin Transactions 2