Transition State Stabilization by SCF 2 -H⋅⋅⋅O Bifurcated Hydrogen Bond

The difluoromethylthio group (SCF H), which is generally considered a highly lipophilic weak hydrogen bonding donor, has attracted special interest from the pharmaceutical and agrochemical industry. Remarkably, there have been relatively few literature investigations of SCF H hydrogen bonding interactions. Here, we report the determination of the hydrogen bond acidity parameter A of the SCF H in the most popularly used electrophilic difluoromethylthiolating reagent. We present kinetic and computational evidence of the RSCF -H⋅⋅⋅O2 bifurcated hydrogen bond for stabilizing the SCF H-transferring transition state, which could cause a reversal of apparent electrophilic reactivity of difluoromethylthiolating and trifluoromethylthiolating reagents. Solvent effects on the RSCF -H⋅⋅⋅O2 bifurcated hydrogen bonds will also be discussed.