Ch. 1 - A Review of General ChemistryWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

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

Concept #1: 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.  

Example #1: Is the following molecule saturated? Is it missing any hydrogens? How many if so?

Example #2: Is the following molecule saturated? Is it missing any hydrogens? How many if so?

Example #3: Is the following molecule saturated? Is it missing any hydrogens? How many if so?

Predicting IHD Structurally

*IHD is also known as the Degree of Unsaturation.

Concept #2: 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?

Example #4: What is the IHD of the following molecule? 

Example #5: What is the IHD of the following molecule? 

Example #6: What is the IHD of the following molecule? 

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.

Concept #3: 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. 

Example #7: What is the IHD for C4H7Cl?  

Example #8: What is the IHD for C6H7N?  

Example #9: What is the IHD for C7H12O2?  

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

Additional Problems
Determine the index of hydrogen deficiency (degrees of unsaturation) for the following molecule. Antipsychotic - Haloperidol = C21H23NO2ClF
Determine the index of hydrogen deficiency (degrees of unsaturation) for the following molecule  Cancer, a tyrosine kinase inhibitor - Bosutinib  
Determine the molecular formula corresponding to the following structure. Calculate the number of degrees of unsaturation from the molecular formula and evaluate whether your calculations agree with the structure shown.  
A certain hydrocarbon has a molecular formula of C5H8 . Which of the following is not a structural possibility for this hydrocarbon? (a) It is a cycloalkane. (b) It contains one ring and one double bond. (c) It contains two double bonds and no rings.  (d) It is an alkyne. 
Determine the molecular formula corresponding to the following structure. Calculate the number of degrees of unsaturation from the molecular formula and evaluate whether your calculations agree with the structure shown.  
Based on the trends above, answer the following questions about the structure of a compound with molecular formula C24H48. Is it possible for this compound to have a triple bond? Is it possible for this compound to have a double bond?
Calculate the IHD, index of hydrogen deficiency, for a compound of molecular formula C5H9O2Br.
Calculate the degree of unsaturation for C6H10S.
What is the  unsaturation number of limonene? A. 0 B. 1 C. 2 D. 3 E. 4 F. 5 G. 6 H. 7 I. 8 J. 9
What is the index of hydrogen deficiency of each of the following molecules?
An acyclic alkane has 20 hydrogen atoms. How many carbon atoms are present in this molecule? (A molecule is acyclic if its structure contains no rings.)   A. 6                       B. 7                      C. 8                          D. 9                       E. 10 F. 11                     G. 12                    H. 13                         I. 14                     J. None of these
Which of the following compounds have the same degree of unsaturation? a.I &amp; II b.I &amp; III c.III &amp; IV d.II &amp; III e.I &amp; IV
Determine the degree of unsaturation of the following formulas.
Calculate the IHD, index of hydrogen deficiency, for a compound of molecular formula C12H18N3F2ClNO3.
How many degrees of unsaturation does the following compound have? A)        4 B)        5 C)        6 D)        7  E)       8
What is the index of hydrogen deficiency of each? (Hint: Think about their MF's)
In each pair below, circle the compound with the largest index of hydrogen deficiency; circle both if the index of hydrogen deficiency is the same.
Expand the following structural representations so as to more clearly show all the atoms and any unshared electron pairs. What are their molecular formulas? Are any of them isomers? 
Expand the following structural representations so as to more clearly show all the atoms and any unshared electron pairs. What are their molecular formulas? Are any of them isomers? 
Expand the following structural representations so as to more clearly show all the atoms and any unshared electron pairs. What are their molecular formulas? Are any of them isomers?
Expand the following structural representations so as to more clearly show all the atoms and any unshared electron pairs. What are their molecular formulas? Are any of them isomers?
Are there any cyclic alkenes with the molecular formula C 41H82?
What can be said about the structure of the carbon skeleton of an aldehyde or ketone with molecular formula C14H28O?
The general molecular formula for alkanes is  CnH2n+2. What is the general molecular formula for:(d) Cyclic hydrocarbons that contain one double bond 
For the following formula, C7H10NBr, calculate the IHD and select all the types of unsaturation that might be present in the molecule based on the IHD. 
Are there any nitriles with molecular formula C50H101N?
Are there any cyclic ethers with molecular formula C48H98O?
Are there any cyclic alkenes with molecular formula C41H82?
Alkane (A) has a molecular formula of C11H20. How many rings are present in alkane (A)?
Alkane (B) has a molecular formula of C14H18. How many rings are present in alkane (B)?
Can a molecule with the molecule formula C34H70O be a ketone? Could it be an alcohol? Could it be an ether? Why or why not?
How many unsaturations are present in the following compound?A. noneB. 2C. 3D. 5E. 6
The degree of unsaturation, or index of hydrogen deficiency, is the number of pi bonds plus rings in a molecule.Specify the degree of unsaturation (index of hydrogen deficiency) of the following formulas:(a) C26H28(b) C11H14(c) C8H4Br3N(d) C19H20(e) C6H10O3(f) C9H12N2(g) C7H8(h) C8H8O3(i) C10H8N2
A compound with the formula C5H8 can be either an alkene or an alkyne.a. Trueb. False 
Which of the following molecules have a Hydrogen Deficiency Index of 2? Select all of the molecules that apply.
Which of the above sections of this molecule would be considered a saturated portion of the molecule? 
The index of hydrogen deficiency for C7H6Br4O2 is 3. Select one: a. True b. False 
An organic compound, pictured below, has the chemical formula C 7H10Cl2. How many degrees of unsaturation are present?a. 1b. 2c. 3d. 4