title: Transition states of strain-promoted metal-free click chemistry: 1,3-dipolar cycloadditions of phenyl azide and cyclooctynes.
abstract: Density functional theory (B3LYP) calculations on the transition states for the Huisgen 1,3-dipolar cycloadditions of phenyl azide with acetylene, cyclooctyne, and difluorocyclooctyne are reported. The low activation energy of the cyclooctyne "strain-promoted" cycloaddition (DeltaE = 8.0) compared to the strain-free acetylene cycloaddition (DeltaE = 16.2) is due to decreased distortion energy (DeltaEd) of cyclooctyne (DeltaDeltaEd = 4.6) and phenyl azide (DeltaDeltaEd = 4.5) to achieve that cycloaddition transition state. Electronegative fluorine substituents on cyclooctyne further increase the rate of cycloaddition by increasing interaction energies.
authors: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA.
authors: Daniel H
authors: DH
authors: Ess
authors: Gavin O
authors: GO
authors: Jones
authors: K N
authors: KN
authors: Houk