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Geometry of Benzene from the Infrared Spectrum

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Elisabetta Cané , Andrea Miani and Agostino Trombetti

Università di Bologna, Dipartimento di Chimica Fisica e Inorganicia, Viale Risorgimento 4, 40136 Bologna, Italy

J. Chem. Educ., 1999, 76 (9), p 1288

DOI: 10.1021/ed076p1288

Publication Date (Web): September 1, 1999

Section:

History, Education, and Documentation

Abstract

The structure of benzene is fully determined once the interatomic distances r_cc and r_CH are obtained from experimental data. This infrared spectroscopy experiment allows the determination of r_cc and r_CH from the rotational analysis of an infrared active band of C₆H₆ and one of its isotopomers, C₆D₆. Here the P and R branches of the n₄ parallel band of C₆H₆ (674 cm^-1) and of C₆D₆ (496 cm^-1) are analyzed to determine the rotational constants B₀ of the ground state of both isotopomers. From B₀ values the moments of inertia are calculated and the r_CC and r_CH distances are obtained. The requirements of the experiment are availability of an IR spectrometer equipped with a KBr beam-splitter working at 0.2 cm^-1 of resolution and a short cylindrical cell fitted with KBr windows. High-performance infrared detectors are not required because the bands recorded are the strongest in the spectrum. To fit the experimental wavenumbers of the R and P branch lines at least a second degree polynomial is needed. Such a mathematical tool is generally available on a PC. The values obtained agree fairly well with the literature data for the rotational analysis of high-resolution spectra. The aim of the experiment can be extended to allow the calculation of centrifugal distortion constants, transition moments, and anharmonic constants.

Keywords (Audience):

Upper-Division Undergraduate

Keywords (Domain):

Physical Chemistry

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

IR Spectroscopy

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This article has been cited by 1 ACS Journal articles (1 most recent appear below).

Modern Developments in the Physical Chemistry Laboratory
Samuel A. Abrash
2007 973 (), 115-151
- Modern Developments in the Physical Chemistry Laboratory
  Samuel A. Abrash
  2007 973 (), 115-151
  Developments in the physical chemistry laboratory since the publication of the germinal text by Schwenz and Moore (1) are categorized and reviewed. The categories examined include modern instrumentation, current topics in chemistry, integrated ...
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