Question

3. Why is it necessary to use structural formulas to represent many organic compounds

rather than molecular formulas?

Answer 1

See below.

Step-by-step explanation:

Because there maybe isomers which have the same molecular formula but different structures.

For example some mono-saccharides have a molecular formula C6H12O6, of which glucose is one, have 8 different structures (isomers).

Answer 2

Structural formulas are helpful because they explain the properties and structure of the compound which empirical and molecular formulas cannot always represent.