Structural Isomers of Butane

Isomerism

Although molecules with the same number and kind of atoms have the same formula, their physical and chemical properties differ.

Types Of Isomerism In Butane

1. Constitutional Isomers-:These are isomers that have the same chemical formula but differ in the connection of their atoms or groups of atoms.

Butane could have two distinct structures depending on how connected they are. Butane comes in both straight and branched chain varieties. Both of these butane structures satisfy the carbon atom’s valency and hence form four bonds. In both butane and isobutane, there are a total of 13 covalent bonds.

As it is a constitutional isomer of butane, it was given the name isobutane. The ‘iso’ group’s structural unit is a carbon atom coupled to hydrogen and two -CH3 groups. Chain isomerism is another name for this phenomenon. These are carbon skeleton isomers with different skeletons.

Figure shows the structure of butane.

2. Conformational isomers are isomers that differ in their conformation (Based on rotation around sigma bond)

Due to free rotation around sigma bonds, different spatial configurations of atoms in molecules can be formed. Conformations are the collective term for all of these arrangements. Because the carbon-carbon single bond in butane is a sigma bond, it is possible to rotate around it. This rotation around the C-C single bond can take place without affecting orbital overlap.

As we know because of the rotation, a large number of spatial layouts are available. This rotation, however, is not completely free. To overcome the torsional strain, an energy barrier of roughly 1-20 kJ mol-1 must be crossed. The repulsive interactions between electron pairs cause this torsional strain. There are two types of conformations that can be made:

The groups surrounding the sigma bond lie exactly behind those of the other in this eclipsed configuration. The eclipse of a conformation can be complete or partial. The energy of a conformation can grow or decrease depending on the same difference.

Staggered Conformation- The groups surrounding the sigma bond are staggered with regard to each other in this conformation. Anti and gauche conformation are the two types of staggered conformation.

Conformational isomers are isomers that differ in their conformation.

Anti conformation, Gauche or skew conformation, eclipsed conformation, and totally eclipsed conformation are the four potential conformations for butane. The conformation with the two methyl groups opposite each other (or 1800 away from each other) is called anti conformation and is the most staggered when rotation takes place around the C2-C3 Link.

Butane anti-conformation

Figure 3: Butane anti-conformation

This conformation is eclipsed when the C2-C3 is rotated at an angle of 600; further rotation at an angle of 600 results in skew conformation.

Butane in a gauche conformation

This conformation can be staggered as well, although the methyl groups will be closer together. As a result, there will be repulsions between the electron pairs, resulting in a 3.8 kJ/mol increase in the energy of gauche conformation. Because the methyl groups are closest to one other in a completely Eclipsed conformation, it is the most unstable. The energy of this fully eclipsed conformation is highest, with 19 kJ/mol higher energy than the anti-conformation.

Butane structural isomers

Butane can be split into two isomers.

Structure of n butane or neo butane

C4H10 is the formula for n- butane.

Figure shows the structure of isobutane.

C4H10 is the formula for isobutane.

2-methylpropane is the IUPAC designation for isobutane. This means that two methylpropane structure formulas are identical to two isobutane structure formulas.

Isomers Of Butene

Butene comes in four different isomers.

C4H8 is the chemical formula for butene.

The structural formula for butene and the IUPAC nomenclature C4H8 are explained below:

structure of but-1-ene

Structure of trans-2-butene

structure of cis-2-butene

structure of isobutene

The geometric isomers of 2 butene are cis-2-butene and trans-2-butene. But-1-ene and but-2-ene (both cis and trans) are position isomers of butene, while isobutene structure and but-1-ene and but-2-ene (both cis and trans) are structural isomers of butene.

Understanding the but-2-ene isomers

Butene is made up of four carbon atoms, two of which are linked together by a double bond. Just as unfettered rotation around the carbon-carbon sigma bond allowed conformational isomerism to occur. Geometrical isomerism is a type of isomerism that occurs as a result of constrained rotation around a carbon-carbon double bond.

Conclusion 

The phenomenon of isomerism occurs when two or more compounds have the same chemical formula but distinct chemical structures. Isomers are chemical compounds with identical chemical formulas but differ in characteristics and atom arrangement in the molecule. Butane isomers include n-butane and isobutane.