Geminal
Molecular-structure relationship
In chemistry, the descriptor geminal (from Latin gemini 'twins') refers to the relationship between two atoms or functional groups that are attached to the same atom. 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. Also the shortened prefix gem may 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.
| Alkane | geminal | vicinal | isolated | |
| Methane | not existing | not existing | ||
| Ethane | not existing | |||
| Propane | ||||
| Substituents on selected dibromoalkanes labeled red. | ||||
The related term vicinal refers to the relationship between two functional groups that are attached to adjacent atoms. This relative arrangement of two functional groups can also be described by the descriptors α and β.
011H NMR spectroscopy
In 1H NMR spectroscopy, the coupling of two hydrogen atoms on the same carbon atom is called a geminal coupling. It occurs only when two hydrogen atoms on a methylene group differ stereochemically from each other. The geminal coupling constant is referred to as 2J since the hydrogen atoms couple through two bonds. Depending on the other substituents, the geminal coupling constant takes values between −23 and +42 Hz.
02Synthesis
Sources and credits
This article is adapted from the Wikipedia article “Geminal”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- Methan Lewis.svg by NEUROtiker, Public domain
- Cyclohexyl methyl ketone to gem-dichloride.png by Baconunderwear at English Wikipedia, Public domain
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