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Origin of threefold methyl torsional potential in methylindoles

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Title Origin of threefold methyl torsional potential in methylindoles
 
Creator SINHA, RK
SINGH, BP
KUNDU, T
 
Subject energy density analysis
internal-rotation barriers
flexing analysis
ethane
toluenes
orbitals
cations
methylindoles
methyl torsion
natural bond orbital (nbo)
hyperconjugation
structural energy
steric energy
 
Description In this article, we present a systematic study on mono-methylindoles to investigate the electronic origin of the threefold symmetric component (V-3) of the methyl torsional potential barrier in the ground electronic state (S-0). The structures and the torsional potential parameters of these molecules were evaluated from ab initio calculation using Hartree-Fock (HF), second order Mollar Plesset perturbation (MP2) and B3LYP density functional level of theories and Gaussian type basis set 6-31G(d, p). Natural bond orbital (NBO) analysis of these molecules were carried out using B3LYP/6-31G(d, p) level of calculation to understand the formation of the threefold V-3 term arising from the changes of various non-covalent interactions during methyl rotation. Our analysis reveals that the contributions from pi orbitals play a dominant role in the barrier height determination in this class of molecules. The threefold term in the barrier arises purely from the interactions non-local to the methyl group in case when the methyl group has two single bonds vicinal to it. On the other hand, it is the local interaction that determines the potential energy barrier when the methyl group has one single bond and one double bond vicinal to it. However, in all these cases, the magnitude of the energy barrier depends on the resonance structure formation in the benzene ring frame upon rotation of the methyl group and, therefore, the energetics of the barrier cannot be understood without considering the molecular flexing during methyl rotation.
 
Publisher SPRINGER
 
Date 2011-08-29T16:18:15Z
2011-12-26T12:58:40Z
2011-12-27T05:49:01Z
2011-08-29T16:18:15Z
2011-12-26T12:58:40Z
2011-12-27T05:49:01Z
2008
 
Type Article
 
Identifier THEORETICAL CHEMISTRY ACCOUNTS, 121(1-2), 59-70
1432-881X
http://dx.doi.org/10.1007/s00214-008-0450-7
http://dspace.library.iitb.ac.in/xmlui/handle/10054/12132
http://hdl.handle.net/10054/12132
 
Language en