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Issue 4, 1984
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Conformational studies by dynamic nuclear magnetic resonance. Part 26. Interconversion barriers between syn- and anti-conformers of isomeric thiophenecarbaldehydes

Abstract

The low-temperature 13C n.m.r. spectra (25.16 MHz) of thiophene-2- and -3-carbaldehyde [(1) and (2)] display line-broadening effects due to the exchange between their S,O-syn- and S,O-anti-conformers. In both cases the free energy of activation for rotation of the –CHO moiety was measured, the values being 10.15 and 8.5 kcal mol–1 for (1) and (2), respectively. In the case of thiophene-3-carbaldehyde (2) the signals of both conformers were detected, the ratios being 97:3 at –140 and 93:7 at –100 °C in favour of the S,O-anti-conformer. In thiophene-2-carbaldehyde (1) the minor conformer (S,O-anti) was present in too small an amount to be unambiguously detected by a conventional spectrometer, but spectra taken with a superconducting instrument (75.48 MHz) revealed ca. 1.5% of this conformer at –100 °C.

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Article type: Paper
DOI: 10.1039/P29840000819
Citation: J. Chem. Soc., Perkin Trans. 2, 1984,0, 819-822
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    Conformational studies by dynamic nuclear magnetic resonance. Part 26. Interconversion barriers between syn- and anti-conformers of isomeric thiophenecarbaldehydes

    L. Lunazzi, G. Placucci, C. Chatgilialoglu and D. Macciantelli, J. Chem. Soc., Perkin Trans. 2, 1984, 0, 819
    DOI: 10.1039/P29840000819

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