Vibrational analysis of buta-1,3-diene and its deutero and 13C derivatives and some of their rotational isomers

Gas phase infrared spectra and corresponding DFT calculations of , -diphenylpolyenes

“…A possible explanation for this finding could be the increased p-electron delocalization between double and single bonds in DPH. This greater p-electron delocalization with increasing chain length has just recently been confirmed using microwave spectroscopy and high level calculations [54,5,55] for the unsubstituted analogues and is also reflected in the bond lengths as shown in Table 3. During the c(C-H) out-ofplane vibration the planar character of the orbitals located at the carbon atoms is decreased.…”

“…The vibrational spectra of unsubstituted polyenes and especially of buta-1,3-diene [1] and hexa-1,3,5-triene [2,3] have extensively been studied and normal coordinate analyses have been carried out by many authors which are cited and discussed in Refs. [4][5][6][7][8]. In the field of a, x-diphenylpolyenes the molecular structures of trans-stilbene (tSB) and cis-stilbene (cSB) in the gas phase have been studied theoretically [9][10][11][12] and by electron diffraction [13,14].…”

Predictive abilities of scaled quantum mechanical molecular force fields: application to 2,3-dimethylbuta-1,3-diene

“…Indeed, the difference between the wavenumbers of the C=C stretching bands of strans-I (m 5 and m 34 , Table 2) are approximately 30 cm -1 , whereas in the case s-gauche-I the difference between the analogous wavenumbers is only *15 cm -1 , see Table 2. This feature of the vibrational spectrum of conjugated p-compounds is typical in going from a planar conjugated structure involving a =C-C= moiety to the corresponding non-planar s-gauche structure [32][33][34].…”

“…The difference in positions of the experimental bands of the synphase and antiphase stretching vibrations of the formal double bonds of I are also characteristic of the skeletal structures of the s-trans-I and s-gauche-I conformers by analogy with buta-1,3-diene [32][33][34]. Indeed, the difference between the wavenumbers of the C=C stretching bands of strans-I (m 5 and m 34 , Table 2) are approximately 30 cm -1 , whereas in the case s-gauche-I the difference between the analogous wavenumbers is only *15 cm -1 , see Table 2.…”

Quantitative infrared absorption cross sections of isoprene for atmospheric measurements

“…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.…”