Draw correct structures, by making a single change for any that are incorrect:

(a)

(b)

(c)

(d)

In many cases, the molecular formula does not completely represent a compound, so it is necessary to draw structural formula for those compounds. For example, Isomers are those compounds which have the same molecular formula but different chemical structures. So it is necessary to identify different isomers by drawing their structural formulas.

To draw a structural formula, always remember that carbon atoms have four bonds, a hydrogen atom has one bond, and each oxygen and nitrogen atom has two and three bonds.

Remember to show required double and triple bonds in the structure and satisfy all the four valencies of carbon by attaching it with hydrogen, attaching functional group or substituent as represented in the parent molecule.

(a) In the given structure of compound (a), the carbon atom has five valencies at the second position, which is not possible because carbon atoms have four bonds, and it can participate in bonding only with four atoms, not five, So the structure (a) is incorrect. The correct structure of the following compound (a) is shown below:

(b) In the given structure of compound (b), we have CH₃ at the first position, which is not possible because the carbon atom has only four bonds, so the structure (b) is incorrect. The correct structure of the following compound (b) is shown below:

(c) In the given structure of compound (c), we have a carbon atom with five valencies at the second position, which is not possible because the carbon atom has only four bonds, so structure (b) is incorrect. The correct structure of the following compound (b) is shown below:

(d) The structure of compound (d) is correct.