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  Home > JCE Print > Journal of Chemical Education > Issues > 2005  > December  >
In the Classroom
A New Exploration of the Torsional Energy Surface of n-Pentane Using Molecular Models and Molecular Modeling Software
Sérgio E. Galembeck, Giovanni F. Caramori, and José Ricardo Romero
Departamento de Química, Universidade de São Paulo, 14040-901 Ribeirão Preto, São Paulo, Brazil
Cover
December 2005
Vol. 82 No. 12
p. 1800
Abstract
This article presents a computational experiment about the conformational analysis of n-pentane that can be performed by advanced undergraduate or beginning graduate students. Initially, the four main conformers were determined using molecular models, and their relative stabilities were estimated by the steric repulsions. The structures of these conformers were drawn in molecular graphics software and were optimized utilizing a force field. Vibrational frequencies were also calculated. The results obtained in this study were compared to benchmark calculations and to other force fields. Conformations were also located by conformational search software. From an estimation of the entropy, it was possible to calculate the Gibbs free energy, the relative population of each conformer, and average 3JHH coupling constants. This experiment exposes the students to several important concepts and techniques such as exploration of the conformational potential energy surface by molecular models or computational techniques and the use of literature to obtain the best available results, experimental or theoretical. It is also able to show that some experimental values represent averages between values for several conformations.
Supplement
An input and output file for optimization of geometry and vibrational analysis for the aa UC is available.
*  Contents JCE2005p1800W.doc (Microsoft Word)
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*  Citation
 Galembeck, Sérgio E.; Caramori, Giovanni F.; Romero, José Ricardo. J. Chem. Educ. 2005 82 1800.
*  Keywords
 Computational Chemistry; Computer-Based Learning; Graduate Education / Research; Laboratory Instruction; Molecular Mechanics / Dynamics; Molecular Modeling; Noncovalent Interactions; Physical Chemistry; Stereochemistry; Theoretical Chemistry; Upper-Division Undergraduate
*  History
 Created:
Last Updated:		 October 25, 2005
November 4, 2005
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