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Origin of methyl torsional barrier in 1-methyl-2-(1H)-pyridone

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Title Origin of methyl torsional barrier in 1-methyl-2-(1H)-pyridone
 
Creator PRADHAN, B
SINGH, BP
NANDI, CK
CHAKRABORTY, T
KUNDU, T
 
Subject pi(asterisk)-sigma(asterisk) hyperconjugation mechanism
internal-rotation barriers
staggered conformation
substituted toluenes
anionic states
ethane
2-pyridone
s-1
 
Description The laser induced fluorescence excitation and single vibronic excitation dispersed fluorescence spectra have been studied for supersonic jet cooled 1-methyl-2(1h)-pyridone. The methyl torsional bands and some low frequency vibrational transitions were assigned for both ground and excited states. The torsional parameters V-3=244 cm(-1) and V-6=15 cm(-1) for the ground state and V-3 = 164 cm(-1) and V-6= 40 cm(-1) for the excited state were obtained. To get the insight into the methyl torsional barrier, ab initio calculations were performed and compared with the experimental results. Origin of potential barrier was traced by partitioning the barrier energy into changes in bond antibond interaction, structural, and steric energies accompanying methyl rotation using natural bond orbital analysis. The role of local interactions in ascertaining the barrier potential reveals that its nature cannot be understood without considering the molecular flexing. The hyperconjugation between CH sigma* and ring pi* observed in lowest unoccupied molecular orbital (LUMO) stabilizes the methyl group conformer that undergoes a 60 degrees rotation in the excited state with respect to that of the ground state, and it is the change in LUMO that plays important role in the excited state barrier formation. (c) 2005
 
Publisher AMER INST PHYSICS
 
Date 2011-07-16T10:56:54Z
2011-12-26T12:49:44Z
2011-12-27T05:35:22Z
2011-07-16T10:56:54Z
2011-12-26T12:49:44Z
2011-12-27T05:35:22Z
2005
 
Type Article
 
Identifier JOURNAL OF CHEMICAL PHYSICS, 122(20), -
0021-9606
http://dx.doi.org/10.1063/1.1901567
http://dspace.library.iitb.ac.in/xmlui/handle/10054/4410
http://hdl.handle.net/10054/4410
 
Language en