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Please use this identifier to cite or link to this item: http://dspace.library.iitb.ac.in/jspui/handle/10054/4411

Title: Origin of methyl torsional barrier in 1-methyl-2(1H)-pyridinimine and 3-methyl-2(1H)-pyridone: II. Ground state
Authors: PRADHAN, B
SINHA, RK
SINGH, BP
KUNDU, T
Keywords: internal-rotation barriers
energy density analysis
natural resonance theory
acetaldehyde
toluenes
orbitals
cations
ethane
Issue Date: 2007
Publisher: AMER INST PHYSICS
Citation: JOURNAL OF CHEMICAL PHYSICS, 126(11), -
Abstract: To get the insight into the electronic structure-methyl torsion correlation in nitrogen heterocyclic molecules, a comparative study on torsion of the methyl group in 1-methyl-2(1H)pyridone (1MPY), 1-methyl-2(1H)pyridinimine (1MPI), and 3-methyl-2(1H)pyridone (3MPY) was carried out using ab initio calculations. To understand the barrier forming mechanism in the ground state and its consequence on the molecular structure, the ground state torsional potential has been investigated by partitioning the barrier energy using the natural bond orbital (NBO) theoretical framework. The NBO analysis reveals that the delocalization energy is the barrier forming term whereas the Lewis energy is always antibarrier for all these molecules. To get further insight into the effect of local electronic structure on the methyl torsional barrier, the individual bond-antibond interactions and structural energy contributions have been investigated. It was found that when the bond order difference between the vicinal bonds does not change appreciably during the course of methyl rotation, the local electronic interactions with the methyl group do not play any decisive role in barrier formation as observed in the case of 1MPY and 1MPI. In these cases, it is the skeletal relaxation during methyl rotation that plays an important role in determining the barrier. On the other hand, if the bond order change is appreciable as is the case for 3MPY, the local interactions alone suffice to describe the origin of the torsional barrier of the methyl group.
URI: http://dx.doi.org/10.1063/1.2566602
http://dspace.library.iitb.ac.in/xmlui/handle/10054/4411
http://hdl.handle.net/10054/4411
ISSN: 0021-9606
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