Variable temperature NMR studies on 3-imino-2,2,4,4-tetramethylcyclobutanones: Gibbs free energy for inversion of groups on nitrogen

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Title: Variable temperature NMR studies on 3-imino-2,2,4,4-tetramethylcyclobutanones: Gibbs free energy for inversion of groups on nitrogen
Author: Chong, Hing-Lun
Abstract: A value for the free energy of activation, or G for the inversion of groups on the imino nitrogen of the title compounds was calculated from data obtained from variable temperature NMR. The coalescence temperature, Tc, is obtained as the temperature at which the non-equivalent methyl resonances of the title compounds collapse to a singlet. G is calculated from G =2.3RTc(10.32 + logTc/k) Eq.3 derived from the Eyring Equation. p-Methoxyphenylimino-2,2,4,4-tetramethyl 3-cyclobutanone (4) is found to possess an energy of activation equal to that of 18.55 kcal/mole with its temperature of coalescence at 118C. p-Nitrophenylimino-2,2,4,4-tetramethyl 3-cyclobutanone (5) is found to have an energy of activation for inversion to be 14.25 kcal/mole. The coalescence temperature found for the nitro derivative was found to be subsequently lower than that of the methoxy, 35C. The G value of N-(2,2,4,4-tetramethyl-3 -cyclobutanone)-p-toluenesulfonamide (16) was found to have a value no greater than 16.42 kcal/mole with a corresponding Tc value of 76C. Whereas, the N-(3,3-Dichloro-2,2,4,4-tetramethyl-3-cyclobutanone)- toluenesulfonamide (17) yielded a value of 15.32 kcal/mole for the inversion energy. The Tc was found to be 56C. The data support the hypothesis that lone pair orbital interaction in the transition state affect the free energy of inversion of groups attached to the imino nitrogen.
Record URI: http://hdl.handle.net/1850/14706
Date: 2003-08

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