We all know that the most common fuel used in our kitchens is LPG. But do you know the major component of this LPG? It’s the fourth homologue of the alkane series- Butane. Butane is a highly flammable, colourless, odourless, easily liquefied gas. Butane Formula is represented as \({{\text{C}}_4}{{\text{H}}_{10}}.\)

Butane is typically used as fuel for cigarette lighters and portable stoves, a propellant in aerosols, heating fuel and a refrigerant. In this article, let’s discuss everything about butane and its chemical formula in detail. Scroll down to learn more!

Butane Formula: Overview

Butane, also known as \({\text{n}}\)-butane, is composed of carbon and hydrogen atoms only so it is classified as a hydrocarbon. It is a four-carbon atom containing saturated hydrocarbon consisting only of sigma bonds. The chemical formula of Butane is \({{\text{C}}_4}{{\text{H}}_{10}}\) and its chemical structure is shown below.

Butane Molar Mass

The molar mass of Butane, \({{\text{C}}_4}{{\text{H}}_{10}} = 4\)(Atomic mass of carbon) \( + 10\) (Atomic mass of hydrogen)

\( = 4\left({12.01} \right) + 10\left({1.007} \right) = 58.11\,{\text{g}}/{\text{mol}}\)

Hence, one mole of Butane weighs \(58.12\) grams.

Butane Hybridisation

Hybridisation results in new hybrid orbitals by mixing up atomic orbitals. These hybrid orbitals are generally of lower energy and suitable for the pairing of electrons to form chemical bonds. In Butane, each carbon atom is \({\text{s}}{{\text{p}}^3}\) hybridised.

The ground state of each carbon atom in an butane molecule has two electrons in its \({\text{2s}}\) orbital and \(1\) electron each in \({\text{2px}}\) and \({\text{2py}}\) orbital. The \({\text{2pz}}\) orbital is empty. In its excited state, one paired electron from the \({\text{2s}}\) orbital jumps to occupy the empty \({\text{2pz}}\) orbital.

Hence, there are four orbitals, \(2{\text{s}},2{\text{px}},2{\text{py}},\) and \({\text{2pz}},\) in each carbon atom that overlaps and form singly paired hybrid orbitals. These orbitals readily accept electrons from other atoms and form a sigma bond.

Hence, in Butane (four carbon atoms), there are sixteen \({\text{s}}{{\text{p}}^3}\) hybridised orbitals. Out of these sixteen orbitals, ten orbitals are involved in \(\left({{\text{s}}{{\text{p}}^3} – {\text{s}}} \right)\) sigma bonding with the hydrogen atoms. The remaining six hybridised orbitals overlap with each other to form three \({\text{C-C}}\) sigma bonds. This is diagrammatically represented as below-

Butane Molecular Geometry

Butane can be viewed as a dimer of an ethyl group. The geometry of the molecule is tetrahedral, with all the carbon atoms being \({\text{s}}{{\text{p}}^3}\) and having bonds of approx \({109.5^ \circ }.\)

Butane Bond Angle

Butane, \({{\text{C}}_4}{{\text{H}}_{10}}\) has a tetrahedral geometry due to \({\text{s}}{{\text{p}}^3}\) hybridisation. The four carbons are bonded together through sigma bonds, and each carbon atom is bonded to three hydrogens at terminal position and two hydrogen atoms in the middle. Each \({\text{H-C-H}}\) angle and \({\text{H-C-C}}\) angle is approximately \({109.5^ \circ }.\)

Butane Dipole Moment

The polarity of the molecule is obtained when there is a net dipole moment in the molecule. Butane is nonpolar because there is no electronegativity difference between the three \({\text{C-C}}\) bond, and the difference in electronegativity between \({\text{C}}\) and \({\text{H}}\) is minimal. Hence, Butane is non-polar.

Butane Lewis Structure

Lewis structures (also known as Lewis dot structures or electron dot structures) are diagrams that represent the valence electrons of atoms within a molecule. Each dot represents an electron, and a pair of dots between chemical symbols for atoms represents a bond.

Total number of valence electrons \( = 4\) (Valence electrons of carbon) \( + 10\) (Valence electron of hydrogen) \( = 4\left( 4 \right) + 10\left( 1 \right) = 26\) valence electrons.
These \(26\) valence electrons are distributed as follows.

In the diagram above, the octet and duplet of carbon and hydrogen atoms are satisfied, respectively.

Butane Skeletal Structure

Butane consists of three \({\text{C-C}}\) bonds and ten \({\text{C-H}}\) bonds. All of the bonds that we see here are single bonds. For this reason, Butane is classified as an alkane. An alkane is a chemical compound that consists of hydrogen and carbon atoms and is only made of single bonds.

Butane Isomerism

Butane is the smallest hydrocarbon of the alkane series that has isomers. Isomers are molecules with the same molecular formula but different structural formulas. This phenomenon is called isomerism.

The four carbon atoms of Butane can arrange in two different manners. They can either arrange in the straight chain of four carbon atoms or can form a chain of \(3\) carbon atoms with one side chain. The straight-chain structure of Butane is known as normal Butane (or \({\text{n}}\)-butane), whereas its only isomer is named isobutane. The IUPAC name of isobutane is \(2\)-methylpropane, in which three carbon atoms from the parent chain and one carbon atom is placed as the side chain at \({\text{C}} – 2\) of the parent chain. All carbon atoms have four valencies which are satisfied either by carbon atoms or hydrogen atoms.

Both molecules have four carbon atoms and ten hydrogen atoms \(\left( {{{\text{C}}_4}{{\text{H}}_{10}}} \right),\) but the atoms are arranged differently in the two compounds.

Properties of Isomers

Isomers are different compounds; hence, they have different properties. Generally, branched-chain isomers have lower boiling and melting points than straight-chain isomers. For example, the boiling and melting points of isobutane are \(- 12\,^\circ {\rm{C}}\) and \(- 160\,^\circ {\rm{C}},\) respectively, compared with \(0\,^\circ {\rm{C}}\) and \(- 138\,^\circ {\rm{C}}\) for \({\text{n}}\)- butane.

Butane Three-dimensional Representation

In Butane, the different spatial arrangements of hydrogen atoms are readily interconvertible by rotation about \({\text{C-C}}\) single bonds resulting in Conformational isomerism. The different structures, known as conformers, are readily interconvertible and thus nonseparable. Conformers are the same molecule that differs only in the rotation of one or more sigma bonds.

To better visualise these different conformations, it is convenient to use a drawing called the Newman projection, we look lengthwise down a specific bond of interest and depict the ‘front’ atom as a dot and the ‘back’ atom as a larger circle.

Conformers of Butane represented through Newman projection are shown below.

In Butane, there are three rotating carbon-carbon bonds, but we will focus on the middle bond between \({\text{C-2}}\) and \({\text{C-3}}.\) This is because the methyl group at the \({\text{C-4}}\) position avoids steric interactions by pointing away from the \({\text{C-1}}\) carbon atom. The rotation around the \({\text{C2-C3}}\) bond, results in two staggered conformers \(\left({{\text{B}}\,\& \,{\text{D}}} \right)\) and two eclipsed conformers \(\left({{\text{A}}\,\& \,{\text{C}}} \right),\) shown below-

This angle between a sigma bond on the front carbon compared to a sigma bond on the back carbon is called the dihedral angle.

At a \({0^ \circ }\) dihedral angle, the two \({\text{C}}{{\text{H}}_3}\) groups (\({{\rm{C}}_{\rm{1}}}\) and \({\text{C4}}\)) are fully eclipsed \(\left({\text{A}} \right)\) as two methyl groups are at minimum distance. At a \({60^ \circ }\) dihedral angle (clockwise), the butane molecule is now in a staggered conformation\(\left({\text{B}} \right).\)

This is more specifically referred to as the gauche conformation of Butane. Although they are staggered, the two methyl groups are not as far apart as they could possibly be.

At \({120^ \circ }\) dihedral angle (clockwise), the butane molecule is now in a second eclipsed conformation \(\left({\text{C}} \right)\) in which both methyl groups are lined up with hydrogen atoms. This is called partial eclipsed structure. At \({180^ \circ }\) dihedral angle (clockwise), the butane molecule is now in a second staggered conformation \(\left({\text{D}} \right)\) called the anti conformation, where the two methyl groups are positioned opposite each other (a dihedral angle of \({180^ \circ }\)).

As with ethane, the staggered conformations of Butane are energy ‘valleys’, and the eclipsed conformations are energy ‘peaks’. However, in the case of Butane, there are two different valleys and two different peaks.

1. The gauche conformation is a higher energy valley than the anti conformation due to steric strain, which is the repulsive interaction caused by the two bulky methyl groups being forced to close together. Steric strain is lower in the anti conformation.
2. In the same way, steric strain causes the eclipsed A conformation – where the two methyl groups are as close together as they can be – to be higher in energy than the two eclipsed \({\text{C}}\) conformations.

The diagram below summarises the relative energies for the various eclipsed, staggered, and gauche conformations.

 Sawhorse Projection

In a sawhorse projection, the backbone carbons are represented by a diagonal line, and the terminal carbons are shown in groups, just as in the Fischer projection. A sawhorse projection can reveal staggered and eclipsed conformations in molecules. Below are the three Sawhorse Projections of Butane.

Sawhorse projection also helps in explaining the stability of conformations. In the staggered form of Butane, the electron clouds of hydrogen and methyl groups are as far apart as possible. Thus, there are minimum repulsive forces, minimum energy and maximum stability of the molecule.

On the other hand, in the eclipsed form, the electron clouds of hydrogen and methyl groups are in close proximity resulting in an increase in electron cloud repulsion.

Hence, the Staggered form is more stable.

Preparation of Butane

Butane occurs in natural gas and crude oil and is formed in large quantities in refining petroleum to produce gasoline. The butanes present in natural gas can be separated from the large quantities of lower-boiling gaseous constituents, such as methane and ethane, by absorption in light oil.

Laboratory Preparation of Butane

1. By Wurtz Reaction:

Butane can be viewed as a dimer of ethyl groups. In the laboratory, Butane may be conveniently synthesised by the Wurtz reaction.

Wurtz’s reaction is an organic chemical coupling reaction wherein sodium metal reacts with two alkyl halides in the environment provided by a solution of dry ether to form a higher alkane along with a compound containing sodium and halogens. When bromoethane and sodium metal are heated in the presence of dry ether, Butane is formed.

\({{\text{C}}_2}{{\text{H}}_5}{\text{Br}} + {\text{Na}} + {{\text{C}}_2}{{\text{H}}_5}{\text{Br}} \to {{\text{C}}_2}{{\text{H}}_5} – {{\text{C}}_2}{{\text{H}}_5} + {\text{NaBr}}\)

2. By hydrogenation of alkenes in presence of a catalyst such as \({\text{Pt}},{\text{Pd}}.\)

On the addition of hydrogen to an alkene (both \(1\)-butene and \(2\)-butene), the double bond of the compound breaks and corresponding alkane is obtained.

Physical Properties of Butane

The physical properties of butane is tabulated below:

Chemical Properties of Butane

The chemical properties of Butane are as follows:

1. The butane moiety is called a butyl group, and related compounds may be formed by replacing a hydrogen atom with another functional group. For example, a butyl group linked to a hydroxyl group yields butanol \(\left({{\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{OH}}}\right).\)

2. Like other hydrocarbons, Butane undergoes complete combustion and produces carbon dioxide and water. It is an exothermic reaction

\(2{{\text{C}}_4}{{\text{H}}_{10}} + 13{{\text{O}}_2} \to 8{\text{C}}{{\text{O}}_2} + 10{{\text{H}}_2}{\text{O}} + {\text{Energy}}\)

3. Combustion may also occur in a limited supply of oxygen, forming carbon monoxide.

\(2{{\text{C}}_4}{{\text{H}}_{10}} + 9{{\text{O}}_2} \to 8{\text{CO}} + 10{{\text{H}}_2}{\text{O}} + {\text{Energy}}\)

4. Butane can react with halogens, especially chlorine and bromine, by radical halogenation. This reaction proceeds through the propagation of the butyl radical, providing both \(1\)-chloro- and \(2\)-chlorobutane, as well as more highly chlorinated derivatives.

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Uses of Butane

The uses of butane are as follows:

1. Butane’s high flammability enables it to be used as a torch. It creates an intensely hot flame that is used to make glass or craft projects. This torch can also be used in a portable stove which can be very important for campers.
2. Butane torch is also commonly used as a kitchen appliance. It is used to caramelise sugar, melt toppings on casseroles, melt cheese, and roast vegetables such as peppers.
3. LPG or liquefied petroleum gas is a product that is usually made by combining Butane and Propane. It is usually used for cooking or even as vehicle fuel.
4. The purest form of Butane can be used as a refrigerant. Adding Butane to gasoline doesn’t increase the flammability of the gasoline but enhances its performance and quality.
5. A highly purified form of isobutane is useful as a propellant aerosol spray.
6. Butane, as a food additive, can usually be found in the form of TBHQ (tert-butylhydroquinone). It is used in crackers, potato chips, microwave popcorn, chicken nuggets, butter, some fast foods, varnish, lacquer, and resin. TBHQ prolongs the shelf life of food. It is also considered safe to consume as long as it is consumed at a low level. 

Summary

Butane is an important component of cooking gas. It has high flammability and hence finds a wide range of uses. Hence, it is essential to learn about its structure and properties. Butane includes three \({\text{C-C}}\) bonds and ten \({\text{C-H}}\) bonds. It is important to note that the purest form of Butane can be utilised as a refrigerant. Furthermore, the butane torch can be utilised as a kitchen appliance. Butane is also used to melt toppings, cheese, roast vegetables, caramelise sugar, etc.

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FAQs on Butane

Q.1. Is \({{\rm{C}}_{\rm{4}}}\) a butane?
Ans: Butane or \({\text{n}}\)-butane is an alkane with the formula \({{\text{C}}_4}{{\text{H}}_{10}}.\) It is also known as \({{\text{C}}_4}.\)

Q.2. Is Butane toxic to humans?
Ans: The toxicity of Butane is low. Butane abuse is caused when there is huge exposure to high concentrations. The predominant effects observed in butane toxicity are central nervous system (CNS) and cardiac effects.

Q.3. Is Butane bad to inhale?
Ans: Yes, Butane is bad to inhale because it causes-
1. Choking
2. Suffocation
3. Swollen throat

Q.4. Is Butane alcohol?
Ans: Butane is not an alcohol, it’s an alkane. The alcoholic homologue of butane is butanol, i.e, \(1\)-butanol and \(2\)-butanol.

Q.5. What is the difference between butane and n-butane?
Ans: There is no difference between butane and \({\text{n}}\)-butane. \({\text{n}}\)-butane is just the more technical, specific name that assures there is no confusion between butane isomers. This representation differentiated between its straight-chain isomer and branched-chain isomer.

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