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High-resolution infrared and electron-diffraction studies of trimethylenecyclopropane ([3]-radialene)



Corey Wright, Joshua Holmes, Joseph W. Nibler, Kenneth Hedberg, James D. White, Lise Hedberg, Alfons Weber, Thomas A. Blake


Combined high-resolution spectroscopic, electron-diffraction, and quantum theoretical methods are particularly advantageous for small molecules of high symmetry and can yield accurate structures that reveal subtle effects of electron delocalization on molecular bonds. The smallest of the radialene compounds, trimethylenecyclopropane, [3]-radialene, has been synthesized and examined in the gas phase by these methods. The first high-resolution infrared spectra have been obtained for this molecule of D3h symmetry, leading to an accurate B0 rotational constant value of 0.1378629(8) cm-1, within 0.5% of the value obtained from electronic structure calculations (density functional (DFT) B3LYP/cc-pVTZ). This result is employed in an analysis of electron-diffraction data to obtain the rz bond lengths (in Å): C-H = 1.072 (17), C-C = 1.437 (4), and C=C = 1.330 (4). The analysis does not lead to an accurate value of the HCH angle but from comparisons of theoretical and experimental angles for similar compounds, the theoretical prediction of 117.5˚ is believed to be reliable to within 2˚. The effect of  electron delocalization in radialene is to reduce the single C-C bond length by 0.07 A compared to that in cyclopropane.
Journal of Physical Chemistry


Radialene, high-resolution infrared spectrum, electron diffraction, molecular structure, DFT calculations


Wright, C. , Holmes, J. , Nibler, J. , Hedberg, K. , White, J. , Hedberg, L. , Weber, A. and Blake, T. (2013), High-resolution infrared and electron-diffraction studies of trimethylenecyclopropane ([3]-radialene), Journal of Physical Chemistry, [online], (Accessed April 16, 2024)
Created May 15, 2013, Updated October 12, 2021