Getting van der Waals Forces Right

I'm actually going to ignore the headline on this article at Chemistry World, although coming up with it must have made someone's day. Once I'd gotten my head back up out of my hands and read the rest of the piece, it was quite interesting. It's a summary of this paper in Nature Chemistry, which used the ingenious system shown to measure what the alkyl-chain interactions are worth in different solvents. The team has now used a synthetic molecular balance to measure the strength of van der Waals interactions between apolar alkyl chains in more than 30 distinct organic, fluorous and aqueous solvent environments. The balance measurements show that the interaction between alkyl chains is an order of magnitude smaller than estimates of dispersion forces derived from measurements of vaporisation enthalpies and dispersion-corrected calculations. Moreover, the team found that van der Waals interactions between the alkyl chains were strongly attenuated by competitive dispersion interactions with the surrounding solvent molecules. There are two ways to look at this, and they're not mutually exclusive. One, which the Chemistry World article takes (in a quote from lead author Scott Cockcroft), is that this could simplify computational approaches to compound interactions, because calculating van der Waals forces is a much more intensive process. If solvent interactions are just going to cancel them out, why spend the resources? And that's true, but it brings up the other question: why ...
Source: In the Pipeline - Category: Chemists Tags: Chemical News Source Type: blogs