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Phenylcyclopropane Energetics and Characterization of Its Conjugate Base: Phenyl Substituent Effects and the C-H Bond Dissociation Energy of Cyclopropane.
- Source :
-
Journal of Organic Chemistry . 10/7/2016, Vol. 81 Issue 19, p9175-9179. 5p. - Publication Year :
- 2016
-
Abstract
- The α-C-H bond dissociation energy (BDE) of phenylcyclopropane (1) was experimentally determined using Hess' law. An equilibrium acidity determination of 1 afforded ΔH°acid = 389.1 ± 0.8 kcal mol-1, and isotopic labeling established that the α-position of the three-membered ring is the favored deprotonation site. Interestingly, the structure of the base proved to be a key factor in correctly determining the proper ionization site (i.e., secondary amide ions are needed, and primary ones and OH- lead to incorrect conclusions since they scramble the deuterium label). An experimental measurement of the electron affinity of 1-phenylcyclopropyl radical (EA = 17.5 ± 2.8 kcal mol-1) was combined with the ionization energy of hydrogen (313.6 kcal mol-1) to afford BDE = 93.0 ± 2.9 kcal mol-1. This enabled the effect of the phenyl substituent to be evaluated and compared to other situations where it is attached to an sp³- or sp²-hybridized carbon center. M06-2X, CCSD(T), G4, and W1BD computations were also carried out, and a revised C-H BDE for cyclopropane of 108.9 ± 1.0 kcal mol-1 is recommended. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00223263
- Volume :
- 81
- Issue :
- 19
- Database :
- Academic Search Index
- Journal :
- Journal of Organic Chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 118665330
- Full Text :
- https://doi.org/10.1021/acs.joc.6b01718