In chemistry, the term geminal refers to the relationship between two atoms or functional groups that are attached to the same atom. The word comes from Latin gemini meaning "twins". A geminal diol, for example, is a diol (a molecule that has two alcohol functional groups) attached to the same carbon atom, as in methanediol.
The prefix gem may also be applied to a chemical name to denote this relationship, as in a gem-dibromide for "geminal dibromide".
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.
The following example shows the conversion of a cyclohexyl methyl ketone to a gem-dichloride through a reaction with phosphorus pentachloride. This gem-dichloride can then be used to synthesize an alkyne.
The related term vicinal refers to the relationship between two functional groups that are attached to adjacent atoms.
Words and music by jimmy nall
When the world is dark, when the lights go down
When the demons walk, when they're all around
There's a light that comes from a place on high
There's a light that comes that the angels shine
And it shines for you, and it shines for me
And it shlnes for all, and it shines for free
When the world is dark, when the demons walk
There's a light that shines like a burning arc
And though I walk through the valley of the shadow
I will fear no evil
And though I walk through the valley of the shadow
I will fear no evil
Since the dawn of time, when the world began
We've borne witness to all the acts of man
How he ruled the earth, when he learned to walk
How he learned to hurt, when he learned to talk
And he's broken laws, and he's broken dreams
And he's broken bones, and ignored the screams
Through the longest day, through the darkest night
There wlll always shine, his redeeming light
And though I walk through the valley of the shadow
I will fear no evll
And though I walk through the valley of the shadow