Journal article

Publication year: 2015

Pages: 7828-7834

Journal: Journal of the American Chemical Society

Volume number: 137

Issue number: 24

DOI Link: https://doi.org/10.1021/jacs.5b03322

Publisher: American Chemical Society

Abstract: 

Matrix-isolation experiments near 3 K and state-of-the-art quantum chemical computations demonstrate that oxalic acid [1, (COOH)₂]
exhibits a sequential quantum mechanical tunneling phenomenon not
previously observed. Intensities of numerous infrared (IR) bands were
used to monitor the temporal evolution of the lowest-energy O–H rotamers
(1cTc, 1cTt, 1tTt) of oxalic acid for up to 19
days following near-infrared irradiation of the matrix. The relative
energies of these rotamers are 0.0 (1cTc), 2.6 (1cTt), and 4.0 (1tTt) kcal mol^–1. A 1tTt → 1cTt → 1cTc isomerization cascade was observed with half-lives (t_1/2) in different matrix sites ranging from 30 to 360 h, even though the sequential barriers of 9.7 and 10.4 kcal mol^–1
are much too high to be surmounted thermally under cryogenic
conditions. A general mathematical model was developed for the complex
kinetics of a reaction cascade with species in distinct matrix sites.
With this model, a precise, global nonlinear least-squares fit was
achieved simultaneously on the temporal profiles of nine IR bands of the
1cTc, 1cTt, and 1tTt rotamers. Classes of both fast (t_1/2 = 30–50 h) and slow (t_1/2
> 250 h) matrix sites were revealed, with the decay rate of the
former in close agreement with first-principles computations for the
conformational tunneling rates of the corresponding isolated molecules.
Rigorous kinetic and theoretical analyses thus show that a “domino”
tunneling mechanism is at work in these oxalic acid transformations.

Harvard Citation style: Schreiner, P., Wagner, J., Reisenauer, H., Gerbig, D., Ley, D., Sarka, J., et al. (2015) Domino Tunneling, Journal of the American Chemical Society, 137(24), pp. 7828-7834. https://doi.org/10.1021/jacs.5b03322

APA Citation style: Schreiner, P., Wagner, J., Reisenauer, H., Gerbig, D., Ley, D., Sarka, J., Csaszar, A., Vaughn, A., & Allen, W. (2015). Domino Tunneling. Journal of the American Chemical Society. 137(24), 7828-7834. https://doi.org/10.1021/jacs.5b03322