D. Bougeard

The vibrational spectra of tert-butyl (tert-butylimino)borane ((CH3)3CBNC(CH3)3) and di-tert-butylethyne ((CH3)3CCCC(CH3)3)

Abstract The i.r. and Raman spectra of tert-butyl(tert-butylimino)borane with fairly pure 10 B and in natural isotopic abundance were recorded in the liquid state. Corresponding spectra were obtained for the isoelectronic di-tert-butylethyne. The fundamental frequencies were assigned in terms of a linear chain and staggered tert-butyl groups ( C 3ν . and D 3 d symmetries for the iminoborane and the ethyne, respectively). Valence force fields were constructed, keeping most of the force constants common for the two compounds. Reasonably good fits were obtained between the experimental and calculated frequencies. When fermi resonance interaction perturbing the 11 BN stretching mode was taken into account the 10 B 11 B isotopic shifts were well predicted from the calculations. The i.r and Raman intensities of the iminoborane and the ethyne spectra were calculated my means of CNDO calculations and the very simple “activity measure” and are discussed in terms of the experimental data.

Determination of the Structures of Organic Molecules by Computer Evaluation and Simulation of Infrared and Raman Spectra

A non-linear molecule with n atoms is able to perform 3n-6 different normal vibrations. Depending on the molecular symmetry these vibrations are visible as bands in the infrared and the Raman spectrum, each with a typical intensity. This means: the frequency and intensity values of both vibrational spectra supply about 3(3n-6) different data for each definite kind of molecules.