Conformational studies by dynamic nuclear magnetic resonance. Part 26. Interconversion barriers between syn- and anti-conformers of isomeric thiophenecarbaldehydes
- 1 January 1984
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 4,p. 819-822
- https://doi.org/10.1039/p29840000819
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.Keywords
This publication has 0 references indexed in Scilit: