Experimental evidence for heavy-atom tunneling in the ring-opening of cyclopropylcarbinyl radical from intramolecular 12C/13C kinetic isotope effects.
The intramolecular (13)C kinetic isotope effects for the ring-opening of cyclopropylcarbinyl radical were determined over a broad temperature range. The observed isotope effects are unprecedentedly large, ranging from 1.062 at 80 degrees C to 1.163 at -100 degrees C. Semiclassical calculations employing canonical variational transition-state theory drastically underpredict the observed isotope effects, but the predicted isotope effects including tunneling by a small-curvature tunneling model match well with experiment. These results and a curvature in the Arrhenius plot of the isotope effects support the recently predicted importance of heavy-atom tunneling in cyclopropylcarbinyl ring-opening.
Gonzalez-James
Ollie M
OM
Department of Chemistry, Texas A&M University, College Station, Texas 77842, USA.
Zhang
Xue
X
Datta
Ayan
A
Hrovat
David A
DA
Borden
Weston Thatcher
WT
Singleton
Daniel A
DA
D002247:Carbon Isotopes / Q000737:chemistry; D003517:Cyclopentanes / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D007700:Kinetics; D015394:Molecular Structure; D013696:Temperature
D002247:Carbon Isotopes; D003517:Cyclopentanes; D005609:Free Radicals