Question

Not counting geometrical isomers. How many isomers can $C_4{H}_8$ have?

• A. 5
• B. 3
• C. 4
• D. Data insufficient

Answer 1

The correct option is A

5

For the formula C₄H₈,

Degree of unsaturation

= (no of carbon atoms) +1-{No 8 H atoms +No halogens-No of nitrogen atoms}

Whenever we encounter sulphur or oxygen we discount them.

Degree of unsaturation is defined as the minimum no of bonds that must be broken to convert the given compound into a saturated open chain compound.

For C₂H₄, D.U=1

In CH₂=CH₂, if we break the double bond (π bond) we get

CH₂=CH₂+H₂ (r)CH₃-CH₃

It may also be defined as the no of hydrogen molecules that need to be added to the given compound to make it an aliphatic alkane.

D.U=no of π bonds+ no of cyclical structures in the compound

For C₄H₈, degree for unsaturation

=4+1-$\frac{8}{2}$=1

So C₄H₈ has on π bond OR one cyclical structure.

So possible structures are:

, ,

CH₃-CH=CH-CH₃

Ans=5 or a