What is the chemical formula for isobutane?

They are both C4H10 but isobutane has another structure, called Isomer

Butane: Isobutane: H H H H H H H H-C-C-C-C-H H-C-C-C-H H H H H HHCHH H

Isobutane comes in Y shape not in series as n-butane.

In refineries, they transform n-butane to iso-buatene. So, they can use it in alkaline units to produce gasoline