OVERTONE CIRCULAR DICHROISM SPECTRA OF A CHIRAL H-C-C-H MOLECULAR FRAGMENT INTERPRETED BY CROSS CORRELATIONS OF CLASSICAL TRAJECTORIES

$^{1)}$L. Laux, V. Pultz, S. Abbate, H.A. Havel, J. Overend, A. Moscowitz, D.A. Lightner, J. Am. Soc., 1982, 104, 4276. $^{2)}$S. Abbate, G. Longhi, J.W. Givens III, S.E. Boiajiev, D.A. Lightner, A. Moscowitz, Applied Spectrosc., 1996, 50 642. $^{3)}$S. Abbate, G. Longhi, D. Cavagnat, L. Lespade, C. Bertucci, P. Salvodori, $4^{th}$ Int. Conference on CD, Bochum, Germany, 1991.Author Institution: Dipartimento di Scienze Biomediche, Universit\`a di Breschia; Chemistry Dept., University of MinnesotaA class of several chiral cyclic molecules containing a $CH_{2}CH_{2}C^{*} H$ fragment exhibit similar infrared circular dichroism spectra, the gross features of which have been elucidated some time ago(1). The corresponding near infrared (NIRCD) spectra however show different behaviors(2,3). In order to explain signs and orders of magnitudes of NIRCD rotational strengths, we ran classical trajectories calculations for a model of the $HCC^{*} H$ fragment, consisting of two coupled dissymetrically disposed CH-stretchings. We allowed for different values of the harmonic frequencies and anharmonicities and also of the interaction force constant. We computed the cross spectra of the two CH stretchings and constructed in this way theoretical NIRCD spectra for overtones up to $\Delta v=6$. The method allows to draw qualitative conclusions about the behavior of local and normal modes in CD spectra