Tetramethyl&shy;ammonium fluoride is the quaternary ammonium salt with the formula (CH)NF. This hygroscopic white solid is a source of “naked fluoride": fluoride ions not complexed with a metal atom. Most other soluble salts of fluoride are in fact bifluorides, HF. Historically, there have been two main approaches to prepare tetramethyl&shy;ammonium fluoride: hydrofluoric acid neutralization of tetramethyl&shy;ammonium hydroxide, and salt metathesis between different ammonium salts and inorganic fluoride sources, such as KF or CsF. Because the fluoride anion is extremely basic, the salt slowly reacts with acetonitrile, inducing dimerization to CHC(NH)=CHCN, which co-crystallizes.