Butene: Structure, Formula, Preparation & Properties

An alkene is a hydrocarbon with a carbon–carbon double bond in chemistry. The term is often used interchangeably with olefin, which refers to any hydrocarbon with one or more double bonds. However, the IUPAC recommends using the term "alkene" only for acyclic hydrocarbons with one double bond; alkadiene, alkatriene, etc., or polyene for acyclic hydrocarbons with two or more double bonds; cycloalkene, cyclooctadiene, etc., for cyclic hydrocarbons; and "olefin" for all cyclic or acyclic hydrocarbons with one or more double bonds.

The stability of the double bond is affected by alkyl groups bound to the sp² hybridised carbon atoms of alkenes. The number of alkyl groups bound to the sp² hybridised carbon atoms can also influence the chemical reactivity of alkenes. As a result, alkenes can be classified according to the number of alkyl groups attached to the C=C structural unit. The degree of substitution is the term for this function.

Monosubstituted alkenes have a single alkyl group bound to the sp² hybridised carbon atom of the double bond. A terminal alkene is an alkene with its double bond at the end of the carbon atom chain. Disubstituted, trisubstituted, and tetrasubstituted alkenes have two, three, or four alkyl groups bound to the carbon atoms of the double bond, respectively.

This article will study butene structure, butene formula, butene structural formula and isomers of butene.

Butene Formula

Butene is an alkene with the formula C4H8 that is also known as butylene. Butene may refer to all of the compounds individually. They are colourless gases that are present in crude oil as a minor constituent in amounts that make extraction impossible. Butene is made by catalytic cracking of long-chain hydrocarbons left over from crude oil refining. Fractional distillation is used to remove butene from a mixture of products produced by cracking.

Butene Structure

Given below is the butene structure:

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Preparation of Butene

Butenes are produced commercially by catalytic dehydrogenation (elimination of hydrogen atoms from the molecule) of butanes, which occurs during the cracking (breaking down of large molecules) of petroleum to create gasoline. The majority of butenes are used in the manufacture of octanes, which are essential components of gasoline. This is accomplished by either allowing the butenes to react with isobutane or by dimerizing (combining two molecules of) butenes to produce octenes, which are then hydrogenated to produce octanes.

Isomers of Butene

Here are Some Structural Isomers of Butene

As already studied, the butene formula is C4H8. These four hydrocarbons all have four carbon atoms and one double bond in their molecules, but their chemical structures are different. These chemical compounds have the following IUPAC and common names:

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Properties of Structural Isomers of Butene 

At room temperature and pressure, all four of these isomers are gases, but they can be liquefied by lowering the temperature or increasing the pressure on them, similar to pressurised butane. These gases are colourless but have distinct odours, and they are extremely flammable. While they are not found in high concentrations in petroleum, they can be made from petrochemicals or by catalytic cracking. The carbon-carbon double bonds make them more reactive than related alkanes, which are more inert compounds in different ways.

These 4-carbon alkenes can serve as monomers in the formation of polymers and have other uses as petrochemical intermediates due to their double bonds. They are used to manufacture synthetic rubber. Isobutylene is a branched alpha-olefin, while but-1-ene is a linear or regular alpha-olefin. But-1-ene, along with other alpha-olefins, is used as one of the comonomers in the manufacture of high-density polyethylene and linear low-density polyethylene in a small percentage. Butyl rubber is generated by cationic polymerization of isobutylene with 2–7% isoprene. Isobutylene is also used to make methyl tert-butyl ether (MTBE) and isooctane, all of which are good for the environment.

Did You Know?

The three sp² hybrid orbitals of each carbon in the double bond are used to form sigma bonds with three atoms (the other carbon and two hydrogen atoms). The pi bond is formed by the unhybridized 2p atomic orbitals that lie perpendicular to the plane provided by the axes of the three sp² hybrid orbitals. This bond is located outside of the main C–C axis, with half of the bond on one side and the other. The pi bond is slightly weaker than the sigma bond, with a strength of 65 kcal/mol.

Since it requires energy to break the alignment of the p orbitals on the two carbon atoms, rotation around the carbon–carbon double bond is limited. As a result, substituted alkenes can be divided into two types of isomers: cis and trans isomers. For molecules with three or four different substituents, the E–Z notation may be used to label more complex alkenes (side groups). For example, in (Z)-but-2-ene ( cis-2-butene), the two methyl groups are on the same side of the double bond, while in (E)-but-2-ene ( trans-2-butene), the methyl groups are on opposite sides. Butene's two isomers have different properties.