Methyl Substitution Destabilizes Alkyl Radicals
- Blokker, Eva
- van Zeist, Willem Jan
- Sun, Xiaobo
- Poater, Jordi
- van der Schuur, J. Martijn
- Hamlin, Trevor A.
- Bickelhaupt, F. Matthias
DOIAbstract
We have quantum chemically investigated how methyl substituents affect the stability of alkyl radicals MemH3−mC⋅ and the corresponding MemH3−mC−X bonds (X = H, CH3, OH; m = 0 – 3) using density functional theory at M06-2X/TZ2P. The state-of-the-art in physical organic chemistry is that alkyl radicals are stabilized upon an increase in their degree of substitution from methyl<primary<secondary<tertiary, and that this is the underlying cause for the decrease in C−H bond strength along this series. Here, we provide evidence that falsifies this model and show that, on the contrary, the MemH3−mC⋅ radical is destabilized with increasing substitution. The reason that the corresponding C−H bond nevertheless becomes weaker is that substitution desta...
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