Alküül

Alküül (alkyl) on substituent in organic chemistry formed by removing one hydrogen atom from an alkane. The general formula is CnH2n+1 and it is commonly denoted as R–, indicating attachment to a larger molecule. Alküül groups are predominantly nonpolar hydrocarbon fragments and can be linear (n-alkyl) or branched. Common examples include methyl (CH3–), ethyl (C2H5–), propyl (C3H7–) and butyl (C4H9–).

The point of attachment defines the class: a primary alküül group is attached to the rest of the molecule via a terminal carbon that is bonded to only one other carbon; secondary via a carbon bonded to two carbons; tertiary via a carbon bonded to three carbons. Branched alküül groups include isopropyl (secondary) and tert-butyl (tertiary).

Cycloalkyl groups, derived from cycloalkanes, are closely related to alküül groups. Examples include cyclopentyl and cyclohexyl. They are often treated as substituents with their own characteristic reactivity.

Nomenclature follows substitutive rules: alküül groups are named as substituents with the suffix -yl (methyl, ethyl, propyl, butyl). When a parent hydrocarbon is present, the molecule is named with the alküül as a substituent, and the parent chain or ring is chosen to give correct locants and overall lowest nomenclature.

Reactivity: alküül groups are relatively inert on their own but participate in reactions that form new carbon–carbon or carbon–heteroatom bonds, such as SN2 substitutions, radical reactions, and various cross-coupling processes. They influence physical properties like solubility and boiling point mainly through chain length and branching. Applications span organic synthesis, polymers, fuels, solvents, and pharmaceuticals.