Question

Calculate the degrees of unsaturation for C7H11N

I know its answer choice B, but why 3?

a. 2

b. 3

c. 4

d. 6

Answer 1

A general formula for calculating the degrees of unsaturation from a molecular formula is the following:
Degrees of Unsaturation = [(Number of Carbons x 2) + 2 - Number of Hydrogens] / 2

For non hydrocarbon elements:
Oxygen--ignore
Halides (F, Cl, Br, I)--count as a hydrogen
Nitrogen--count as one half of a carbon

Here:
number of carbon = 7 + 1/2 = 7.5
number of Hdrogen = 11

Degrees of Unsaturation = [(Number of Carbons x 2) + 2 - Number of Hydrogens] / 2
= [(7.5*2)+2 - 11]/2
=(15+2 - 11)/2
= 6/2
= 3

Answer: b