Chemists have found lots of examples of hydrogen bonding

chemists have found lots of examples of hydrogen bonding Hydrogen atoms, armed with a lone electron, generally form a single bond with one other atom. For example, hydrogen can form a pretty strong covalent bond – made of a shared pair of electrons - with a carbon atom. The bond is found in every organic compound, from petrol to paraquat.

In contrast, other atoms that are willing to loosely share their electrons with a hydrogen atom can sometimes form a weaker 'hydrogen bond' with it – as though the hydrogen atom forms a bridge between two other atoms (see picture).

But over recent years, chemists have found lots of examples of hydrogen bonding that don't quite fit the classic Pauling definition, and the Gold Book has long been due an update, says Gautam Desiraju, a chemist at the Indian Institute of Science in Bangalore. He was on a task force established by IUPAC in 2005 to revise the current, conservative definition.