Ultrasonic relaxation and internal rotation in thiophen- and furan-2-carbaldehyde

1 January 1969

journal article
research article
Published by Royal Society of Chemistry (RSC) in J. Chem. Soc. A

p. 713-717
https://doi.org/10.1039/j19690000713

Abstract

The rates of isomerisation of the equilibrium XO-trans⇌ XO-cis in pure liquid furan-and thiophen-2-carbaldehydes have been measured by using the ultrasonic-pulse technique. In furan-2-carbaldehyde these rates were found to be complementary to a recent n.m.r. study. From the Eyring rate equation and the temperature dependance of the exchange rates the activation enthalpies for the XO-cis→ XO-trans reaction are of the order 10–11 kcal./mole for furan- and thiophen-2-carbaldehydes. In furan-2-carbaldehyde these energy barriers are compared to those found in spectroscopic studies of torsional frequencies. The Arrhenius rate parameters for furan-2-carbaldehyde (E= 11·5 ± 0·5 kcal./mole and A= 2 ± 0·8 × 10¹³ sec.^–1) were derived from the combined ultrasonic and n.m.r. data. These kinetic parameters are in reasonable agreement with a simple mechanism for internal rotation.

Keywords

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