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, Δ G ‡, 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 1 H 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.
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Rushton et al. (2007) studied this question.