Theoretical study on the molecular structures of toluene, para-fluorotoluene, para-chlorotoluene, and 4-methylpyridine and their sixfold internal rotational barriers

Chen, P. C.; Chang, Fenfen

doi:10.1002/(sici)1097-461x(2000)77:4<772::aid-qua8>3.0.co;2-6

Cited by 8 publications

(3 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A 4-picoline-methyl- d 3 molecule has three deuterium atoms in the methyl group, which can be detected by ESDIAD, if the molecule were adsorbed in an upright configuration . The methyl group of 4-picoline has an extremely low internal rotation barrier, 0.5860 meV in the gas phase . The thermal energy at 80 K (7 meV) is enough therefore to activate the internal rotational motion of the methyl group.…”

Section: Resultsmentioning

confidence: 99%

Adsorption Geometry of 4-Picoline Chemisorbed on the Cu(110) Surface: A Study of Forces Controlling Molecular Self-Assembly

Ahner

Yates

2002

J. Am. Chem. Soc.

View full text Add to dashboard Cite

The adsorption of 4-picoline (4-methylpyridine) on the Cu(110) surface has been studied with time-of-flight electron stimulated desorption ion angular distribution (TOF-ESDIAD) and other methods. Using deuterium labeling in the methyl group and hydrogen labeling on the aromatic ring, it has been possible to separately monitor by TOF-ESDIAD the C-D bond directions and the C-H bond directions in the adsorbed molecule. These triangulation measurements have led to a detailed understanding of the conformation of the adsorbed molecule relative to the Cu(110) crystal lattice, allowing one to witness changes in the molecular conformation as adsorbate-adsorbate interactional effects take place for increasing coverages. At low coverages, the molecule adsorbs by the N atom at an atop Cu site with the aromatic ring parallel to the <001> azimuth and with the molecular axis inclined 33 (+/- 5) degrees along the <001> azimuth. As rows of 4-picoline molecules form long range ordered chain structures oriented along the <112> azimuth, the aromatic ring twists 29 degrees about the inclined molecular axis as a result of forces between the adsorbate molecules. The initial tilting of the molecular axis at low coverage is likely due to the interaction of the positive-outward dipole with its image in the substrate. The ring twist may result from dipoleminus signdipole forces between the adsorbate molecules in the rows formed tending to form nested parallel pyridine rings. These studies are the first to apply the TOF-ESDIAD method for the measurement of the direction of chemical bonds at more than one molecular location within an adsorbed molecule and the new method is named electron stimulated desorption-molecular triangulation (ESD-MT). The results obtained give information of importance in understanding the factors which control conformational effects during the molecular self-assembly of complex adsorbed molecules on surfaces.

show abstract

Section: Resultsmentioning

confidence: 99%

Adsorption Geometry of 4-Picoline Chemisorbed on the Cu(110) Surface: A Study of Forces Controlling Molecular Self-Assembly

Ahner

Yates

2002

J. Am. Chem. Soc.

View full text Add to dashboard Cite

show abstract

“…The B3LYP calculated internal rotational barriers agreed best with the experimentally derived value. 25 We used the CASSCF method to calculate the geometry and harmonic frequencies of the planar and orthogonal configurations. The planar configuration had higher energy and one imaginary frequency, À21.7 cm À1 , while the orthogonal configuration had lower energy and no imaginary frequency, indicating that the orthogonal configuration is the most stable one for the ground state of p-ClT.…”

Section: Geometries Of the Ground State And Several Excited Statesmentioning

confidence: 99%

Multireference calculations of the fluorescence, phosphorescence and photodissociation of p-chlorotoluene

Liu

Lunell

2005

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

Equilibrium geometries and vibrational frequencies of the ground and some excited states of p-chlorotoluene were calculated by the complete active space self-consistent field (CASSCF) method. Multi-reference CASSCF second order perturbation theory (MSCASPT2) calculations were performed on the vertical excitation energies of six singlet and triplet excited states. The potential energy curves along the Cl-C6H4CH3 bond distance of a number of low-lying singlet and triplet excited states were calculated by the CASPT2 method based on CASSCF partially optimized geometries. The fluorescence and one component of the dual phosphorescence observed experimentally were clearly explained by the CASPT2 calculated transition energies. According to those CASPT2 potential energy curves, the photodissociation of p-chlorotoluene at 266 nm was attributed to the predissociation of the first triplet excited state after its intersystem crossing with the first singlet excited state. The internal rotation and substitution effects of methyl on the photodissociation were discussed in detail.

show abstract

“…Because of its industrial importance 5,6 and chemical properties, toluene has been extensively studied by using vibrational spectroscopy 7 and computational chemistry. [8][9][10] The methyl group was recognized to be an important factor accelerating the intramolecular vibrational redistribution. 11,12 Quantum computations were successfully used in the past to interpret torsionally induced absorption 13 and supersonic jet spectra.…”

Section: Introductionmentioning

confidence: 99%

Raman spectral evidence of methyl rotation in liquid toluene

Kapitán

Hecht

Bouř

2008

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

In order to rationalize subtle details in the liquid phase toluene Raman backscattering spectra, an analysis was performed based on a quantum-mechanical Hamiltonian operator comprising rotation of the methyl group and the angular dependence of vibrational frequencies and polarizability derivatives. The separation of the methyl torsion from the other vibrational motions appears to be necessary in order to explain relative intensity ratios of several bands and an anomalous broadening of spectral intensity observed at 1440 cm(-1). These results suggest that the CH3 group in the liquid phase rotates almost freely, similarly as in the gaseous phase, and that the molecule consequently exhibits effectively C(2v) point group symmetry. A classical description and an adiabatic separation of the methyl rotation from other molecular motion previously used in peptide models is not applicable to toluene because of a strong coupling with other vibrational motions. Density functional computations, particularly the BPW91 functional, provide reasonable estimates of harmonic frequencies and spectral intensities, as well as qualitatively correct fourth-order anharmonic corrections to the vibrational potential.

show abstract

Theoretical study on the molecular structures of toluene, para-fluorotoluene, para-chlorotoluene, and 4-methylpyridine and their sixfold internal rotational barriers

Cited by 8 publications

References 21 publications

Adsorption Geometry of 4-Picoline Chemisorbed on the Cu(110) Surface: A Study of Forces Controlling Molecular Self-Assembly

Adsorption Geometry of 4-Picoline Chemisorbed on the Cu(110) Surface: A Study of Forces Controlling Molecular Self-Assembly

Multireference calculations of the fluorescence, phosphorescence and photodissociation of p-chlorotoluene

Raman spectral evidence of methyl rotation in liquid toluene

Contact Info

Product

Resources

About