Ab initio structures and vibrational analysis of the isoprene conformers

Quantitative infrared absorption cross sections of isoprene for atmospheric measurements

“…3, to an out-of-plane asymmetric CH 3 stretch, ν 23 , and the peak at 2985 cm −1 to ν 4 , a symmetric CH 2 stretch. Subsequent work (Traetteberg et al, 1984;Bock et al, 1987) was in agreement with these assignments. , however, concluded that 2956 cm −1 was not a fundamental mode.…”

“…The conformation analysis was reexamined by Traetteberg et al (1984), who, using gas electron diffraction and theoretical techniques, determined that the gauche form did indeed exist, that it accounted for ∼ 5 % at room temperature, and that the planar s-cis was unlikely to be present at all. Subsequent ab initio analyses (Bock et al, 1987;Bock and Panchenko, 1989) confirmed this, although the angle of the gauche conformer was uncertain. More recent work, including a detailed study of a series of 10 methyl-substituted 1,3-butadienes (Squillacote and Liang, 2005), established the gauche s-cis conformer of isoprene to be 2.46 kcal mol −1 (10.29 kJ mol −1 or 860 cm −1 ) less stable than the planar strans form, while the planar s-cis conformer was theoretically determined to be 3.16 kcal mol −1 less stable than the planar s-trans form.…”

“…While the consensus in the literature supports this conclusion, there has been some dispute regarding the scis conformer (Fig. 2b), its fractional abundance at room temperature, and whether the conformer is planar or gauche (Traetteberg et al, 1984;Bock et al, 1987;Cias et al, 2007;Panchenko and De Mare, 2008;Squillacote and Liang, 2005;Allodi et al, 2008). Compton Squillacote and Liang (2005) using the G3B3 method.…”

“…Nonetheless, there is an abundance of studies on the vibrational spectra of isoprene, but most have focused on elucidating the structure and identifying its conformational equilibria (Compton et al, 1976;Traetteberg et al, 1984;Bock et al, 1987;Bock and Panchenko, 1989;; fundamental modes typically were assigned during the structural analyses. Based on these previous vibrational assignment studies and structural determinations, and the need for quantitative absorption cross-section data, this paper makes the first comprehensive report of the infrared band strengths of isoprene.…”

Vibrational spectra of 1,3,5-hexatriene and methylated derivatives—II. The coupling pattern for lateral methylation

“…For these compounds a good agreement is found in CT between calculated and observed vibrational wavenumbcrs. A more recent study of isoprene [40] supports the CT isoprene values. CT mainly uses a modified Urey-Bradley force field [36, 411 whereas we use a valence type of force field.…”