Methylene group

The blue- marked methylene group (top row from left to right: in methylene chloride , methylenecyclopropene and a triplet carbene; bottom row from left to right: in a malonic acid ester and in propane )

The methylene group is a functional group with the formal unit CH ₂ . The simplest chemical compound with a methylene group is methylene (CH ₂ ), a very reactive carbene .

According to the IUPAC nomenclature, the prefix methylene can be used for a double bonded substituent (= CH ₂ ), a double bonded group (–CH ₂ -) and to denote chain and ring members . The designation for the highly reactive carbene as “methylene molecule” represents a special case . The grouping = CH ₂ is now known as methylidene.

Activated methylene compounds are substances in which the carbon-hydrogen bond of a methylene group is particularly acidic due to electron-withdrawing substituents , for example malonic acid esters and β-keto esters. These esters are CH-acidic compounds and are often used as starting materials in the Knoevenagel reaction , the Michael addition or similar reactions.

The name methylene (from the Greek méthy = alcoholic drink and hýlē = wood) was coined in 1834 by Jean Baptiste Dumas and Eugène-Melchior Péligot and refers to the name of methanol as “wood alcohol”, the dehydrated form of which is formally the methylene group.

Methylene chloride (CH ₂ Cl ₂ ) is a commonly used name for dichloromethane .

See also

• Methyl group (CH ₃ , often short: Me)
• Methine group (CH)
• Phenyl group (C ₆ H ₅ , often short: Ph)
• Phenylene group (C ₆ H ₄ )

literature

• Entry to carbenes . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.C00806 .

Individual evidence

1. ↑ Saarland University: Seminar: Systematic Nomenclature in Organic Chemistry ( Memento from September 11, 2014 in the Internet Archive ), summer semester 2005 (PDF; 1.1 MB).