write the structural formulae of isomers of butane?

Butane is a simple alkane with the molecular formula C₄H₁₀. The question asks for the structural formulae of its isomers. To understand why and how isomers exist for butane, and how to draw their structures, let's break down the question in depth.

What is Isomerism?

Isomerism refers to the phenomenon where compounds have the same molecular formula but different arrangements of atoms. This difference in arrangement can affect both physical and chemical properties. In organic chemistry, structural isomers (also called constitutional isomers) have the same molecular formula but different connectivity of atoms. In the case of butane, this is known as chain isomerism (also called skeletal isomerism), because the carbon atoms are connected in different ways—either in a straight chain or with a branch.

Understanding Butane

Butane contains four carbon atoms. According to the general formula for alkanes (CnH2n+2), butane’s molecular formula is C₄H₁₀. When arranging these four carbon atoms, only two distinct arrangements are possible without breaking any rules of valency and without forming rings (which would be a different class of isomers, not relevant here).

Two Structural Isomers of Butane

1. n-Butane (Normal Butane)

• Structure: All four carbon atoms are connected in a straight, unbranched chain.
• Structural Formula:CH₃-CH₂-CH₂-CH₃
• Description: This is the simplest arrangement for four carbon atoms and ten hydrogens, giving each carbon four bonds by fulfilling the valence requirements.

2. Isobutane (2-Methylpropane)

• Structure: Three carbon atoms form a straight chain, and the fourth carbon atom is attached as a branch to the second carbon of the main chain (a methyl group).
• Structural Formula:(CH₃)₂CH-CH₃
• Description: This is the only possible branched arrangement for the C₄H₁₀ formula, resulting in a different connectivity pattern compared to n-butane.

Visualizing the Structural Formulae

• n-Butane:

CH₃-CH₂-CH₂-CH₃

(Linear chain, no branches)

• Isobutane (2-Methylpropane):

(CH₃)₂CH-CH₃

(Three-carbon main chain with a methyl branch on the middle carbon)

These formulae show how the same molecular formula can give rise to different molecules due to different carbon atom arrangements.

Why Only Two Isomers?

With four carbon atoms, the possible arrangements are limited. All other attempts to draw different structures either repeat the existing isomers or violate the valence rules for carbon and hydrogen. No other structurally distinct isomer of C₄H₁₀ exists under normal conditions.