Q. What is structural formula and how to write it?

Ans.

To represent an organic molecule, a structural formula is often used. As a structural formula shows how the atoms in a molecule are bonded to each other, it gives more information than does a molecular formula. Therefore, to represent compounds clearly, structural formulas should be used.

For example, it is ambiguous to represent butane by its molecular formula C₄H₁₀ because another compound, 2-methylpropane, has the same molecular formula. Here are two different structural formulas for these two compounds that both have the molecular formula C₄H₁₀:

Note: The 2 in 2-methylpropane designates that the carbon in the methyl group branch is attached to the second carbon in the propane chain.

For convenience, the structural formulae of butane and 2-methylpropane are often written in shortened form as:

These are condensed structural formulas. In a condensed structural formula single bonds are usually omitted (except those joining additional branches to the main carbon skeleton). Double and triple bonds, however, are diagrammed.