Structure and conformations of isoprene by vibrational spectroscopy and gas electron diffraction

Isoprene-mediated lithiation of imidazole derivatives. Mechanism considerations

“…4.7%) corresponding to the gauche (or skew), the s-cis being too scarcely populated to be detected, according to vibrational spectroscopy and gas electron diffraction studies. 21 According to our calculations for the equilibrium depicted in Equation 3, three conformers were also detected, corresponding to the s-trans-7 (180º dihedral), 22 , can be rationalized taking into consideration that the calculations were performed for the isolated anions in gas phase without the stabilizing effect of the counterions. Thus, the observed energetic balance is principally due to the contribution of NMI (as the only neutral and stable species in the equilibrium).…”

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.…”

“…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.…”

“…2c) was not observed. 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.…”