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17O-Dynamic NMR and DFT Investigation of Bis(acyloxy)iodoarenes
Laboratoire de RMN Haute Résolution CP 160/08, Université Libre de Bruxelles, Av. F.-D. Roosevelt 50, 1050 Brussels, Belgium
Dipartimento di Scienze Chimiche e Geologiche, Università di Cagliari, Complesso Universitario, S.S. 554, Bivio per Sestu, I-09042 Monserrato (CA), Italy
* Authors to whom correspondence should be addressed.
Received: 11 September 2012; in revised form: 10 October 2012 / Accepted: 19 October 2012 / Published: 26 October 2012
Abstract: Bis(acetoxy)iodobenzene and related acyloxy derivatives of hypervalent I(III) were studied by variable temperature solution-state 17O-NMR and DFT calculations. The 17O-NMR spectra reveal a dynamic process that interchanges the oxygen atoms of the acyloxy groups. For the first time, coalescence events could be detected for such compounds, allowing the determination of activation free energy data which are found to range between 44 and 47 kJ/mol. The analysis of the 17O linewidth measured for bis(acetoxy)iodobenzene indicates that the activation entropy is negligible. DFT calculations show that the oxygen atom exchange arises as a consequence of the [1,3]-sigmatropic shift of iodine. The calculated activation barriers are in excellent agreement with the experimental results. Both the 17O-NMR and DFT studies show that the solvent and chemical alterations, such as modification of the acyl groups or para- substitution of the benzene ring, hardly affect the energetics of the dynamic process. The low I-O Wiberg bond index (0.41–0.42) indicates a possible explanation of the invariance of both the energy barrier and the 17O chemical shift with para-substitution.
Keywords: hypervalent iodine; fluxional compounds; sigmatropic shift; 17O-NMR; chemical exchange; Density Functional Theory
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Fusaro, L.; Mocci, F.; Luhmer, M.; Cerioni, G. 17O-Dynamic NMR and DFT Investigation of Bis(acyloxy)iodoarenes. Molecules 2012, 17, 12718-12733.
Fusaro L, Mocci F, Luhmer M, Cerioni G. 17O-Dynamic NMR and DFT Investigation of Bis(acyloxy)iodoarenes. Molecules. 2012; 17(11):12718-12733.
Fusaro, Luca; Mocci, Francesca; Luhmer, Michel; Cerioni, Giovanni. 2012. "17O-Dynamic NMR and DFT Investigation of Bis(acyloxy)iodoarenes." Molecules 17, no. 11: 12718-12733.