It has been concluded that acetylcholine and related compounds must be in the gauche (bent) configuration when bound to the nicotinic receptor. Beers and Reich's studies on cholinergic receptors in 1970 showed a relationship affecting whether a compound was muscarinic or nicotinic. They showed that the distance from the centre of the quaternary N atom to the van der Waals extension of the respective O atom (or an equivalent H-bond acceptor) is a determining factor. If the distance is 0.44 nm, the compound shows muscarinic properties—and if the distance is 0.59 nm, nicotinic properties dominate.)