The degree of unsaturation (number of rings plus pi bonds) of 4-nitrostyrene (1-ethenyl-4-nitrobenzene) is to be found from its molecular formula. Treat the nitro group as one $N$ atom attached to two $O$ atoms. Give the answer as the nearest integer.

Numerical answer type, tolerance 0.5.

Answer: 6

4-Nitrostyrene is

O X_{2} N - C X_{6} H X_{4} - CH = CH X_{2}

, formula

C X_{8} H X_{7} NO X_{2}

. Degree of unsaturation

= (2 C + 2 + N - H) /2 = (16 + 2 + 1 - 7) /2 = 6

. This agrees with 4 for the benzene ring, 1 for the vinyl group and 1 for the

N = O

of the nitro group.