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Determination of the Rotational Barrier for Kinetically Stable Conformational Isomers via NMR and 2D TLC

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Gregory T. Rushton , William G. Burns , Judi M. Lavin , Yong S. Chong , Perry Pellechia and Ken D. Shimizu

Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208

J. Chem. Educ., 2007, 84 (9), p 1499

DOI: 10.1021/ed084p1499

Publication Date (Web): September 1, 2007

Section:

History, Education, and Documentation

Abstract

An experiment to determine the rotational barrier about a C_aryl–N_imide single bond that is suitable for first-semester organic chemistry students is presented. The investigation begins with the one-step synthesis of a N,N′-diaryl naphthalene diimide, which exists as two room temperature-stable atropisomers (syn and anti). The students then estimate the rotational barrier, ΔG^‡, by following the reequilibration of the two isomers using two-dimensional thin-layer chromatography. A more accurate determination of the rotational barrier is conducted by a ¹H NMR time study. The synthesis, purification, and kinetics experiments can be carried out within two, three-hour laboratory sessions using commercially available reagents and instrumentation found in most undergraduate laboratories.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Laboratory Instruction

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Alcohols

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