What is the approximate lifetime of an SN2 transition state complex?

2018-03-17 10:25:53

Imagine some SN2 reaction involving an aliphatic sp3 carbon with a halide leaving group (e.g. iodide or bromide). Given the rise of femtosecond spectroscopy (e.g. using a mode-locked Ti:sapphire laser) and even attosecond spectroscopy, I'm curious if there are any studies that have measured the properties and approximate lifetime of the SN2 transition state complex? I guess that this is in the $\approx$ picosecond regime alongside the timescales for a bond stretching dynamics (e.g. between oxygen and hydrogen on a water molecule), however, is there a more precise value that is now known?

I am be curious about results from quantum mechanical simulations (using e.g. Jaguar from the Schrodinger computational chemistry suite) for SN2 reactions?

I'll specify that I'm referring to a "concerted" SN2 reaction, not, for example, the kind of reaction described in: [Chandrasekhar, J., Jorgensen, W. L. Energy profile for a non-concerted SN2 reaction in solution. J. Am. Chem. Soc.

  • 26-60 femtoseconds depending upon impact angle for $\ce{F- + CH3Cl}$ according to Mugnai et al. (Table IV.)

    2018-03-17 10:42:14