Illustrated Glossary of Organic Chemistry

Measles: An atom having one or more lone pairs is said to have measles. The presence of measles may allow for resonance. Two adjacent atoms with measles may have a weakened bond due to electron pair repulsion.


   

This oxygen atom has measles. Carbon has
a open valence shell. This cation has resonance.
In hydrogen peroxide, lone pair/lone pair repulsion weakens the
oxygen-oxygen bond. This molecule slowly decomposes at room
temperature, fragmenting into two hydroxyl radicals.