Geminal

Also the shortened prefix gem may be applied to a chemical name to denote this relationship, as in a gem-dibromide for "geminal dibromide".

[citation needed] The concept is important in many branches of chemistry, including synthesis and spectroscopy, because functional groups attached to the same atom often behave differently from when they are separated.

Geminal diols, for example, are easily converted to ketones or aldehydes with loss of water.

[2] The related term vicinal refers to the relationship between two functional groups that are attached to adjacent atoms.

[3][4] The following example shows the conversion of a cyclohexyl methyl ketone to a gem-dichloride through a reaction with phosphorus pentachloride.