Degree of Unsaturation Calculator

Created by Komal Rafay
Reviewed by Dominik Czernia, PhD candidate and Jack Bowater
Last updated: Apr 06, 2022

Determining the degree of unsaturation becomes convenient and efficient with our degree of unsaturation calculator, which finds the unsaturation index of certain molecules.

If you have a knack for chemistry, then you might have wondered what is the index of hydrogen deficiency, or maybe you are interested in the formula of the degree of unsaturation. Whatever the reason for visiting our tool, you can learn all of it in the following article!

Degree of unsaturation calculator

The degree of unsaturation calculator is a convenient tool that allows you to use the molecular formula of an organic molecule to find the number of rings and pi bonds found in the compound. This is useful when you don't know the arrangement of the molecule and want to try and find it.

The degree of unsaturation calculator requires you to input the molecular formula (not molecular weight), i.e., the number of carbon, hydrogen, nitrogen, and halogen atoms present in the compound.

Remember, oxygen is a divalent atom so, it does not contribute to the degree of unsaturation. In fact, *any atom that is divalent has no impact on a hydrocarbon's or any other organic compound's degree of unsaturation.

Degree of unsaturation meaning in organic chemistry

The degree of unsaturation is significant in determining molecular structure as it helps to determine the number of pi bonds and rings present in an organic molecule.

The degree of unsaturation has other names too. These DoU definitions are:

  • Index of hydrogen deficiency (IHD);
  • Unsaturation index; and
  • Double bond equivalents.

Degree of unsaturation is often not enough to determine the structure of an unknown molecule alone. Other methods, such as nuclear magnetic resonance and infrared radiation, provide much more exact information, as degree of unsaturation doesn't tell you if a molecule has two double bonds or one triple bond (e.g., C4H6).

Another degree of unsaturation meaning is double bond equivalent. It determines the total number of rings or pi bonds formed in an organic compound. In this case, saturation means that no more hydrogens can be added to the molecule by breaking double bonds, triple bonds, or rings. This is similar to the other meanings of saturation, in particular the point in a solution where the solvent is no longer able to dissolve more solute.

Degree of unsaturation formula

Determining the degree of unsaturation is simple and DoU formula is straightforward:

DoU = 1/2 * (2 + 2 * C - H + N - X)

where:

  • DoU - Degree of unsaturation;

  • C - Number of carbon atoms;

  • H - Number of hydrogen atoms;

  • N - Number of nitrogen atoms; and

  • X - Number of halogen atoms.

How to calculate the degree of unsaturation in organic chemistry?

To calculate the degree of unsaturation of an organic molecule, you need to know the number of each atom that makes up the molecule. The resultant degree of unsaturation allows you to interpret the number of rings or pi bonds present in your structure.

One of the most important aspects of organic chemistry is molecular structure. In some cases, you wish to find the number of double bonds, triple bonds, and rings without drawing the entire structure (some molecules can contain hundreds of atoms!). To find the degrees of unsaturation:

  1. Count the number of carbon, hydrogen, nitrogen, and halogen atoms present in the compound.
  2. Double the number of carbons and from this number subtract the number of hydrogens and halogens.
  3. Add 2 plus the number of nitrogens to the resultant.
  4. Divide the new number by two.

After using the DoU formula, you'll need to interpret the result. For instance, if your degree of unsaturation value is two, it means that the molecule contains either two double bonds, a triple bond, two rings, or a combination of the above.

FAQ

What is degree of unsaturation?

The degree of unsaturation of an organic compound is a number that determines the amount of rings and pi bonds contained within the compound.

The degree of unsaturation (DoU) is also known as:

  • Index of hydrogen deficiency (IHD);
  • Double bond equivalent; and
  • Unsaturation index.

The DoU equation makes studying the structure of organic compounds more convenient and accurate because we can determine the number of hydrogens bonded with each carbon, thus eliminating any confusion.

Can degree of unsaturation be negative?

No, the degree of unsaturation of an organic molecule cannot be a negative number because it represents the number of rings or pi bonds present in that compound.

Consider that you can't say there are negative two pi bonds in a compound.

Does a halogen add to the degree of unsaturation?

No, halogen atoms do not change the degree of unsaturation (DoU) of an organic compound. They are, however, included in its calculation as they replace hydrogen atoms, and ignoring them would lead to inaccurate results.

How can I calculate hydrogen from degree of unsaturation?

You can calculate the number of hydrogen atoms for an organic compound using the degree of unsaturation formula provided you have the value of the degree of unsaturation.

The formula of the degree of unsaturation is:

DoU = 1/2 × (2 + 2 × C - H + N - X)

You can rearrange this formula to calculate hydrogen as:

H = 2 + 2 × C + N - X - 2 × DoU
where:

  • DoU - Degree of unsaturation;

  • C - Number of carbon atoms;

  • H - Number of hydrogen atoms;

  • N - Number of nitrogen atoms; and

  • X - Number of halogen atoms.

Komal Rafay
Number of carbon atoms (C)
Number of hydrogen atoms (H)
Number of nitrogen atoms (N)
Number of halogens atoms (X)
Degree of unsaturation (DoU)
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