Hydrocarbons fall into two categories:Saturated and Unsaturated- and both of these terms describe the number of hydrogens that carbon is bonded to.

## The difference between saturated and unsaturated molecules.

The equation 2n + 2 (where n = #carbons) predicts the number of hydrogens that an organic molecule should contain to be considered saturated.

- If the total number of hydrogens < 2n + 2, then the molecule is unsaturated.

Are the following molecules saturated?

**Hint:** You can figure this out without using the 2n + 2 rule.

## Is the following molecule saturated?

## Is the following molecule saturated?

## Is the following molecule saturated?

*IHD is also known as the *Degree of Unsaturation*.

## What index of hydrogen deficiency is.

Basically the IHD is an easy way for us to compare how unsaturated a molecule is compared to another.

- 1 IHD = Compound is missing 2 hydrogens.
- Rings/Double bonds = 1 IHD
- Triple Bonds = 2 IHD

What is the IHD of the following molecules?

## What is the IHD of the following molecule?

## What is the IHD of the following molecule?

## What is the IHD of the following molecule?

Unfortunately, the structure of a compound will not always be drawn for us. In that case, we use the following technique.

## How to use IHD with molecular formula.

*****If your professor taught you a different method, that’s fine! Whatever helps you get the right answer.

## What is the IHD for C4H7Cl?

## Calculating IHD using molecular formula

## Calculating IHD using molecular formula

Awesome job. Now we know how to easily calculate and compare the number of hydrogens that are missing for all types of compounds.

- a. How many vinylic hydrogens does cyclopentene have? b. How many allylic hydrogens does it have?
- Determine the degree of unsaturation and then draw possible structures for noncyclic compounds with the follow...
- Determine the degree of unsaturation and then draw possible structures for noncyclic compounds with the follow...
- a. If a hydrocarbon has nine carbon atoms, three double bonds, and one ring, how many hydrogen atoms must it h...
- c. Cholesterol, C27H46O, has only one pi bond. With no additional information, what else can you say about its...
- b. Calculate the number of elements of unsaturation implied by the molecular formula C6H12. Hint: If you pre...
- (•) Calculate the index of hydrogen deficiency for the following molecular formulas and structures. (c)
- (•) Calculate the index of hydrogen deficiency for the following molecular formulas and structures. (b)
- What is the index of hydrogen deficiency for each of the following molecular formulas? (d) C₉H₁₂N₂O₂
- a. Count the elements of unsaturation in parsalmide, ethynyl estradiol, and dynemicin A.