Hindered internal rotation in some singly methylated trans-stilbenes

Journal Article · Wed Jun 01 00:00:00 EDT 1988 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.454422· OSTI ID:5218513

Spangler, L H; Bosma, W B; van Zee, R D; Zwier, T S

The fluorescence excitation and several dispersed fluorescence spectra for supersonically cooled p-methyl-trans-stilbene and the two m-methyl-trans-stilbenes are presented. Despite significant spectral congestion present in these molecules which contain low frequency modes and internal rotation structure, nearly complete assignments of the excitation spectra are given. One notable transition is assigned as a combination of a nontotally symmetric vibration and a nontotally symmetric level of the methyl rotor. All three species have a ground state barrier to internal rotation of approx.28 cm/sup -1/. Excited state barriers and conformational changes observed on excitation are 150 cm/sup -1/ and 35/sup 0/ for p-Me, and 80 cm/sup -1/ and 60/sup 0/, and 186 cm/sup -1/ and 30/sup 0/ for the two m-Me compounds. The p-Me compound shows a threefold barrier to internal rotation rather than a sixfold one, indicating that the two meta positions are inequivalent. The large differences in barrier height and conformational change on excitation between the two meta isomers, whose origins are separated by 207 cm/sup -1/, confirm this inequivalence.

• Research Organization: CLS-2, Los Alamos National Laboratory, Los Alamos, New Mexico 87545
• OSTI ID: 5218513
• Journal Information: J. Chem. Phys.; (United States), Vol. 88:11
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
STILBENE
CONFORMATIONAL CHANGES
FLUORESCENCE
METHYLATION
MOLECULAR BEAMS
ROTATION
SUPERSONIC FLOW
VIBRATIONAL STATES
AROMATICS
BEAMS
CHEMICAL REACTIONS
ENERGY LEVELS
EXCITED STATES
FLUID FLOW
HYDROCARBONS
LUMINESCENCE
MOTION
ORGANIC COMPOUNDS
400102* - Chemical & Spectral Procedures