# Degree of unsaturation

1. Oct 24, 2014

### phoenixXL

Question
Find out the degree of unsaturation in a compound having the molecular formulae C9H6N4.

Attempt
The point lies in making the possible structure(s).
The structure that I felt possible is as follows

In the compound above there are 8-π electrons,
Hence the degree of unsaturation is 8(Ans)

Problem

The problem comes from the topic of structural isomerism and the book says the answer to be 9

2. Oct 24, 2014

### Staff: Mentor

Hint: you are aware of the fact degree of unsaturation for cyclohexane - despite the compound being saturated - is 1?

In other words, degree of unsaturation is not only about pi electrons. There are formulas to calculate degree of unsaturation based on the molecular formula alone (without any structural information).

3. Oct 24, 2014

### phoenixXL

Okay, I didn't knew about that.
I looked Wikipedia and found that rings are counted as a degree of unsaturation, therefore I get the missing "1" from my answer. Also I was unaware of the formula(curious to see its derivation).
Thank You.

4. Oct 24, 2014

### Staff: Mentor

There is no derivation - it is more like a definition.

5. Nov 2, 2014

$DU = 1 + \frac{1}{2}∑[n_i (v_i - 2)]$ where ni is the number of atoms of an element and vi is the valency of that element. Note that this gives you the total number of rings and π bonds.