butan2yl

Butan-2-yl, commonly known as the sec-butyl group, is an alkyl substituent derived from butane by removing a hydrogen from the second carbon. As a substituent, it appears as the fragment -CH(CH3)CH2CH3 attached to a parent molecule.

Nomenclature and synonyms: The formal IUPAC name is butan-2-yl. It is widely referred to as sec-butyl in common use. Abbreviations such as s-Bu are found in some contexts, particularly in shorthand chemical notation. The group is one of several butyl substituents, alongside n-butyl, isobutyl (2-methylpropyl), and tert-butyl.

Structure and stereochemistry: The attachment carbon in butan-2-yl is secondary, bearing one hydrogen, one methyl substituent, and a propyl chain. This secondary center means the group can be chiral when the parent molecule is unsymmetrical, giving rise to potential enantiomers in certain compounds.

Occurrence and applications: Butan-2-yl appears in a wide range of organic molecules, including sec-butyl esters, sec-butyl ethers, and sec-butyl amides. It is encountered in pharmaceutical intermediates, agrochemicals, and various organic syntheses as a nonpolar, carbon-rich fragment that can influence lipophilicity and steric profile. The group is also considered in discussions of protecting groups and in the design of reagents where a secondary alkyl substituent is advantageous.

Properties and safety: As a substituent, butan-2-yl itself is not a standalone compound with a fixed set of properties; its influence on a molecule depends on context. Related sec-butyl reagents (for example, sec-butyl halides or alcohols) share typical alkyl-halogens and alcohol hazards, including flammability and irritation. Proper handling, ventilation, and personal protective equipment are advised when working with related reagents.

See also: n-butyl, isobutyl, tert-butyl.