Studying the vibration frequencies and infrared absorption stresses of cyclo-tributane benzene and assigning the energy of its thermal breakdown products to the hexagonal planar radialin compound using quantum mechanics calculations.

Abstract

MINDO/3-FORCES, PM3 and ab initio calculations were carried out for the
vibration frequencies, IR absorption intensities and normal coordinates of the
tricyclobutabenzene (D3h) compound at its calculated equilibrium geometry.
Assignment of the modes of vibration (3N-6) was done depending on the picture of
their modes drawn applying the DRAW. MOL routine.
The potential energy curve for thermal cracking of tricyclobutabenzene compound
was obtained by changing the distance of the terminal C-C bonds of the cyclobutane
rings using semiemperical quantum mechanical method (PM3) to find the reaction
path. The thermal cracking results of tricyclobutabenzene compound was converted it
to the planar 6-Radialine (D3h) compound which had the higher energy and less stable
than the tricyclobutabenzene compound.
Interesting relations between the different modes of the IR calculation spectra were
also was found on inspecting their frequencies.
CH str. (planar 6-Radialine) > CH str. (tricyclobutabenzene)
νCH str.(symmetric) > νCH str. (asymmetric)
νCC str.(asymmetric) > νCC str.(symmetric)
δ(CH2 (scissoring)) > δ(CH2 (rocking))
γ (CH2 (waging)) > γ (CH2 (twisting))
δ (CC) > γ (CC)