gemdihalide

Gem-dihalide, or geminal dihalide, is a molecule in which two halogen atoms are attached to the same carbon atom. This arrangement, known as a geminal substitution pattern, can occur with identical halogens (1,1-dihaloalkanes) or with mixed halogens (for example CH2ClF). The term “gem” reflects two substituents on the same atom.

Common examples of simple gem-dihalides include dichloromethane (CH2Cl2), dibromomethane (CH2Br2), and diiodomethane (CH2I2). Mixed-halogen examples are also encountered, such as CH2ClF, illustrating that two halogen substituents may be present on the same carbon, even if they are different halogens. Gem-dihalides can also be part of more complex frameworks where the two halogens are attached to a saturated carbon within a larger molecule or, in some cases, on a double-bonded carbon in 1,1-dihaloalkenes.

Properties and reactivity are generally governed by the presence of two bulky, electron-withdrawing substituents on a single carbon. The C–X bonds in gem-dihalides are typically reactive toward various transformations, enabling downstream functionalization. Because two halogens occupy the same carbon, these compounds often serve as versatile intermediates in organic synthesis, where they can be converted in subsequent steps to extend carbon skeletons, introduce alkynes through dehalogenation, or participate in rearrangements and cyclization processes under appropriate conditions.

In summary, gem-dihalides are a useful class of organohalogen compounds defined by two halogen substituents on one carbon, with wide-ranging applications as synthetic intermediates and building blocks in chemistry.