The chemical formula for brown sugar is C12H22O11. Brown sugar and normal table sugar are both sucrose. Both types of sugar have the same chemical formula and relatively the same amount of sucrose.
Brown sugar gets its distinctive color from the presence of molasses. Molasses adds to the flavor of the sugar and also ensures that the sugar is softer and moister than granulated sugar. This enables the sugar to retain more moisture when used for baking and produces baked goods that stay fresher longer.
Manufacturers create brown sugar or derive it naturally from sugar cane. Natural brown sugar is sucrose that retains a small amount of natural molasses from the partially evaporated sugar cane juice.