Solvents are usually considered to be passive participants in chemical reactions – simply a liquid environment that allows substances that react to come together. Now Arthur Bragg, Molly Cavanagh and Benjamin Schwartz of the University of California have shown that this simple idea is not the case in certain circumstances.

The team prepared neutral sodium atoms in the solvent tetrahydrofuran using two separate methods – by adding an electron to a positive sodium ion in one; and by taking an electron away from a negative ion in the other. They discovered that it took the solvent and the neutral sodium atoms twice as long to reach equilibrium after negative sodium atoms were neutralized compared with positive atoms. This is contrary to linear response theory, which states that this would not happen if the solvent atoms were simply adjusting to a newly appeared neutral sodium atom without regard for how it came into being.

Further reading

A E Bragg, M C Cavanagh and B J Schwartz 2008 Science 321 1817.