geminal

In chemistry it is called geminal (from Latin. Gemini "twins") when two identical functional groups (for example, halogens, such as, fluorine , chlorine or bromine ) to the same carbon - atom within a chain or a ring system bound. Deviating definitions do not exclude different substituents , but point out that they are usually similar substituents.

Comparison of geminal with vicinal and isolated substitution patterns.

	Alkane	geminal	vicinal	isolated
methane			does not exist	does not exist
Ethane				does not exist
propane
Red marked substituents on selected dibromoalkanes.

Further terms describing the relative arrangement of two functional groups are vicinal , isolated, and α and β positions .

¹ H-NMR spectroscopy

In ¹ H- NMR spectroscopy , the coupling of two hydrogen atoms located on the same carbon atom is referred to as geminal coupling . It only occurs when two hydrogen atoms on a methylene group differ stereochemically from one another. The geminal coupling constant is referred to as ² J because the hydrogen atoms couple together across two bonds. Depending on the other substituents, the geminal coupling constant assumes values ​​between −23 and +42 Hz.

Individual evidence

1. ^ Brockhaus ABC Chemie , VEB F. A. Brockhaus Verlag Leipzig 1965, p. 462.
2. ↑ entry on geminal. In: Römpp Online . Georg Thieme Verlag, accessed on December 29, 2014.
3. ^ H. Günther: NMR spectroscopy; Basics, concepts and applications of proton and carbon-13 nuclear magnetic resonance spectroscopy in chemistry. 3rd revised and expanded edition, Georg Thieme Verlag, Stuttgart 1992, p. 103.
4. ^ DH Williams, I. Fleming: Structure clarification in organic chemistry; An introduction to the spectroscopic methods. 6th revised edition, Georg Thieme Verlag, Stuttgart 1991, p. 109.