Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

1. A Review of General Chemistry

Degrees of Unsaturation

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

Definition of Saturation

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The difference between saturated and unsaturated molecules.

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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?

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

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Is the following molecule saturated?

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Is the following molecule saturated?

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4

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Is the following molecule saturated?

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Predicting IHD Structurally

*IHD is also known as the Degree of Unsaturation.

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What index of hydrogen deficiency is.

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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?

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What is the IHD of the following molecule?

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What is the IHD of the following molecule?

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What is the IHD of the following molecule?

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Predicting IHD using Molecular Formula

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

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How to use IHD with molecular formula.

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

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What is the IHD for C4H7Cl?

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Calculating IHD using molecular formula

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Calculating IHD using molecular formula

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