Conformational Information from Vibrational Spectra of Styrene, trans-Stilbene, and cis-Stilbene

Abstract

Two electron correlation theories, second-order Møller−Plesset perturbation (MP2), and density functional (DFT) methods have been adopted to obtain fully optimized structures of styrene, trans-stilbene, and cis-stilbene. Full geometry optimizations with MP2 shows that the nonplanar conformations of styrene and trans-stilbene are preferred by 0.24 (styrene) and 0.80 kcal/mol (trans-stilbene), respectively. However, B3LYP, BLYP, and BVWN prefer a planar conformation contradicting the MP2 results. Due to the disorder of the crystal, X-ray experimental data of CC double bond length of trans-stilbene seem to be too short. Vibrational spectra of these molecules are calculated at the BLYP/6-31++G** level without any empirical scaling. The agreement with experiment is excellent, some normal modes are reassigned. The dependence of the IR spectrum as a function of conformation in the 700−800 cm-1 region allows the determination of the solution-phase conformation. Both styrene and trans-stilbene are planar in solution, implying that these molecular conformations are mainly determined by the intermolecular forces rather than intramolecular ones.

Simulation of Single Molecule Inelastic Electron Tunneling Signals in Paraphenylene−Vinylene Oligomers and Distyrylbenzene[2.2]paracyclophanes

“…Discrepancies between experiment and calculations (and between different levels of theory) concerning the planarity in these species stem form the notoriously flat potential surface involving torsional rotation about C-C bonds joining the phenyl and vinyl groups. 76 In our HF/3-21G calculations we impose a planar configuration; thus, there are some imaginary frequencies associated with the torsional motion; we ignore these modes in the calculation of the conductance and IETS signals. Panels A and B of Figure 4 show the simulated conductance and IETS intensities as a function of the applied bias, respectively.…”

Crystal Structure of 2-(4-Hydroxy-3-Methoxyphenyl)-6- (4-Hydroxy-3-Methoxystyryl)-1-Methyl-2, 3-Dihydropyridine-4 (1H)-One by X-Ray Powder Diffraction

“…Meanwhile the double bonds C12-C17 and C10-C11 (1.365 and 1.366 Å respectively) become longer compared to the C=C bond in ethylene which is 1.334-1.339 Å (Choi, 1997). The bond length of C12-C17 is comparable to the value of the corresponding bond in 1, 3-cyclohexendione in its crystalline enol form measured by inelastic incoherent neutron scattering spectra (Hudson et al, 2004), which is 1.361 Å.…”

Investigation on the Growth, Structural and Third Order Nonlinear Optical Properties of 4-Ethoxy-4-N-Methyl-4-Stilbazoliumhexafluorophosphate (EMSHP) Single Crystal

“…The optical nonlinearities of instrumental atoms is forasmuch as of high level of electron delocalization and it is the primary distribute of the perceptible or IR range [23]. The third-order NLO properties of EMSHP were scrutinized utilizing Z-scrutinize order to make up one's inclination the third supplication nonlinear refractive index (n 2 ) and nonlinear absorption co-efficient (β) [24,25] utilizing He-Ne optical maser (5 mW) of wavelength at 632.8 nm was utilized as a spring and the well coldness across is 0.5 mm.…”