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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 16 (2011) pp 175-182

Unexpected Degeneracy in the Hückel Description of Tetramethyleneethane

Emilio Martínez Torres

Facultad de Educación, Departamento de Química Física, Universidad de Castilla-La Mancha, 13003 Ciudad Real, Spain,
Received January 23, 2011. Accepted March 1, 2011.

Published: 15 July 2011

Abstract. It is often the case that the degeneracy of the energy levels is higher than that required by symmetry. This paper describes a simple case of excessive degeneracy that occurs in the Hückel description of the planar conformation of tetramethyleneethane molecule. It is shown that this degeneracy is due to the use of a simplified Hamiltonian which ignores all non-nearest-neighbor interactions and whose symmetry is higher than that of the molecule. This case may be useful for teaching purposes because it covers a wide variety of basic group theoretical concepts and their connection with quantum chemistry.

Key Words: In the Classroom; physical chemistry; quantum mechanics

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