Butyl
Table of Contents
The butyl group is an alkyl substituent with four carbon atoms and nine hydrogen atoms, derived from butane (C4H10) by removing one hydrogen atom. Its general formula is –C4H9, where one carbon attaches to another atom or group. The name “butyl” follows the IUPAC system, with “but–“ denoting four carbons and “–yl” indicating that it is a substituent. [1-4]
A common compound containing this group is n-butyl acetate (CH3COO(CH2)3CH3), widely used as a solvent in paints, lacquers, and adhesives due to its good solubility and pleasant odor.
Isomeric Forms
The butyl group has four structural isomers, differing in how its carbon atoms are arranged and attached. [2,3]
| Common Name | Preferred IUPAC Name | Structure | Attachment | Description |
|---|---|---|---|---|
| n-Butyl | Butyl | –CH2CH2CH2CH3 | Terminal carbon | Straight-chain |
| sec-Butyl | Butan-2-yl | –CH(CH3)CH2CH3 | Secondary carbon | Branched structure |
| Isobutyl or iso-Butyl | 2-methylpropyl | –CH2CH(CH3)2 | Primary carbon | Branched with a methyl group |
| tert-Butyl | tert-Buty | –C(CH3)3 | Tertiary carbon | Highly branched and compact |
Although all have the same formula (C4H9–), their structural differences affect boiling point, steric bulk, and reactivity.
The butan-2-yl (sec-butyl) group is chiral because its second carbon is attached to four different substituents: –H, –CH3, –CH2CH5, and –R. This stereocenter gives rise to two enantiomers—(2R)-butan-2-yl and (2S)-butan-2-yl.
Structure and Bonding [1]
- Hybridization: Each carbon atom in the butyl group is sp3 hybridized, forming four sigma (σ) bonds. All C–C and C–H bonds are single covalent bonds.
- Geometry: The group exhibits tetrahedral geometry around each carbon atom, with bond angles close to 109.5°. Depending on the isomer, the overall structure may appear straight or branched.
- Polarity: The butyl group is nonpolar because carbon and hydrogen have nearly equal electronegativities. When attached to a polar functional group (such as –OH or –COOH), it reduces overall polarity and decreases water solubility while enhancing solubility in organic solvents.
Compounds Containing Butyl Groups
Many important organic compounds contain butyl or its isomeric forms as substituents. These compounds are widely used as solvents, intermediates, and industrial chemicals. [5]
| Compound Name | Chemical Formula | Common Uses and Applications |
|---|---|---|
| n-Butyl alcohol (1-butanol) | CH3CH2CH2CH2OH | Solvent in paints and adhesives; used in cosmetics and perfumes |
| sec-Butyl alcohol (2-butanol) | CH3CH(OH)CH2CH3 | Solvent; intermediate for methyl ethyl ketone (MEK) |
| Isobutyl alcohol (2-methyl-1-propanol) | (CH3)2CHCH2OH | Solvent in coatings and inks; used in plasticizers and flavorings |
| tert-Butyl alcohol (2-methyl-2-propanol) | (CH3)3COH | Fuel additive; intermediate in synthesis |
| n-Butyl acetate | CH3COO(CH2)3CH3 | Solvent in coatings and nail polish removers |
| tert-Butyl chloride | (CH3)3CCl | Alkylating agent in organic synthesis; used to prepare tert-butyl derivatives |
| isobutylamine | (CH3)2CHCH2NH2 | Intermediate in pharmaceuticals, herbicides, and flavoring agents. |
| tert-Butylamine | (CH3)3CNH2 | Production of rubber chemicals, agrochemicals, and pharmaceuticals. |
Chemical Reactivity
The reactivity of the butyl group depends largely on the functional group it is attached to. This can be illustrated using butyl halides. The tert-butyl carbocation is highly stable, making tert-butyl bromide very reactive in an SN1 reaction. In contrast, n-butyl bromide forms a less stable primary carbocation and is therefore much less reactive. The overall reactivity order for SN1 reactions is:
tert-butyl bromide > sec-butyl bromide > n-butyl bromide
The butyl group is a versatile substituent that influences the structure, reactivity, and solubility of organic compounds. Its industrial importance is highlighted by butyl rubber, a durable, flexible polymer used worldwide. The group’s adaptability makes it essential in the design of modern materials, fuels, and solvents.
One significant industrial application of the butyl group is in butyl rubber (isobutylene–isoprene rubber, IIR), a copolymer of isobutylene and a small amount of isoprene. The presence of the butyl structure imparts air impermeability, flexibility, and chemical resistance, making the material ideal for tires, inner tubes, sealants, and protective coatings. Its nonpolar and flexible carbon chain gives the rubber its durability and elasticity.
