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

“How are the following two molecules related to each other?”

Does this sound familiar? This is one of the most important questions you will have to answer in Organic Chemistry 1. 

Definition of Constitutional Isomers

Concept #1: What is a constitutional isomer?

Constitutional isomers are molecules with identical atoms but different connectivity

Constitutional Isomer Flowchart

Concept #2: Using the flowchart to determine isometric relationships.

Example #1: How are the following two compounds related?

Are they different molecules, constitutional isomers, or identical? 

Pair A

Pair B

Example #2: How are the following two compounds related?

Is there a choice we can rule out immediately? 

Example #3: How are the following two compounds related?

So now you should have a pretty good idea of how to solve questions asking for molecular relationship.  

Additional Problems
Consider each pair of compounds below and determine whether  the pair represent the same compound, constitutional isomers, or different compounds that are not isomeric at all:
Consider each pair of compounds below and determine whether  the pair represent the same compound, constitutional isomers, or different compounds that are not isomeric at all:
Consider each pair of compounds below and determine whether  the pair represent the same compound, constitutional isomers, or different compounds that are not isomeric at all:
Consider each pair of compounds below and determine whether  the pair represent the same compound, constitutional isomers, or different compounds that are not isomeric at all:
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? 
Which of the hydrocarbons in each of the following groups are isomers?
Which of the hydrocarbons in each of the following groups are isomers?  
Which of the hydrocarbons in each of the following groups are isomers?
For each of the following pairs of compounds, identify whether the compounds are constitutional isomers or different representations of the same compound:
For each of the following pairs of compounds, identify whether the compounds are constitutional isomers or different representations of the same compound:
For each of the following pairs of compounds, identify whether the compounds are constitutional isomers or different representations of the same compound:
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider the three compounds shown below and then answer the questions that follow:  (a) Which two compounds are constitutional isomers? 
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Consider each pair of structural formulas that follow and state whether the two formulas represent the same compound, whether they represent different compounds that are constitutional isomers of each other, or whether they represent different compounds that are not isomeric.
Choose the compound pair that are not constitutional isomers:
True or False: The following 2 compounds are constitutional isomers of each other.
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? 
Which choice best describes the relationship that exists between the pair of structures?A. IdenticalB. Constitutional isomersC. Resonance structuresD. No relationship exists
Which choice best describes the relationship that exists between the pair of structures?A. Identical B. Constitutional isomersC. Resonance structures D. No relationship exists
Which one of the following compound(s) is constitutional isomers of spiro[2.2]pentane?
QUESTION 4 Which one of the following compounds is an isomer of CH3CH2CH2CH2OH? 
Which two of these four structure are of the same structural isomer? 
Which of the following compounds are isomers?
Which of the following molecules are constitutional isomers?a. All of them are constitutional isomersb. I and IIc. I and IIId. I and III