High-resolution infrared spectroscopy of cubane, C8H8

Abstract

Carbon-cage molecules have generated a considerable interest from both experimental and theoretical point of views. We recently performed a high-resolution study of adamantane (C$_{10}$H$_{16}$), the smallest hydrocarbon cage belonging to the diamandoid family. There exist another family of hydrocarbon cages with additional interesting chemical properties: the so-called Platonic hydrocarbons that comprise dodecahedrane (C$_{20}$H$_{20}$) and cubane (C$_8$H$_8$). Both possess C--C bond angles that deviate from the tetrahedral angle (109.8$^{\circ}$) of the $sp^3$ hybridized form of carbon. This generates a considerable strain in the molecule. Cubane itself has the highest density of all hydrocarbons (1.29 g/cm$^3$). This makes it able to store larges amounts of energy, although the molecule is fully stable. Up to now, only one high-resolution study of cubane has been performed on a few bands [2].

We report here a new wide-range high-resolution study of the infrared spectrum of cubane. The sample was synthesized in Bari upon decarboxylation of 1,4-cubanedicarboxylic acid thanks to the improved synthesis of literature [3]; its ${}^{1}$H and $^{13}$C NMR, FTIR, and mass spectrometry agreed with reported data [4]. Several spectra have been recorded at the AILES beamline of the SOLEIL French synchrotron facility. They cover the 800 to 3100 cm$^{-1}$ region. Besides the three infrared-active fundamentals ($\nu_{10}$, $\nu_{11}$ and $\nu_{12}$), we could record many combination bands, all of them displaying a well-resolved octahedral rotational structure. We present here a preliminary analysis of some of the recorded bands, performed thanks the SPVIEW and XTDS software, based on the tensrorial formalism developed in the Dijon group [5].

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{\footnotesize\noindent[1] O. Pirali, V. Boudon, J. Oomens, M. Vervloet, {\em J. Chem. Phys.\/}, {\bf 136}, 024310 (2012).\newline

[2] A. S. Pine, A. G. Maki, A. G. Robiette, B. J. Krohn, J. K. G. Watson, Th. Urbanek, {\em J. Am. Chem. Soc.\/}, {\bf 106}, 891--897 (1984).\newline

[3] P. E. Eaton, N. Nordari, J. Tsanaktsidis, P. S. Upadhyaya, {\em Synthesis\/}, {\bf 1}, 501, (1995).\newline

[4] E. W. Della, P. T. Hine, H. K. Patney, {\em J. Org. Chem.\/}, {\bf 42}, 2940 (1978).\newline

[5] Ch. Wenger, V. Boudon, M. Rotger, M. Sanzharov and J.-P. Champion, {\em J. Mol. Spectrosc.\/}, {\bf 251} 102--113 (2008).}