Constitutional Isomers

“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

Constitutional isomers are molecules with identical atoms but different connectivity

Constitutional Isomer Flowchart

Concept: Using the flowchart to determine isometric relationships.

6m

Example: How are the following two compounds related?

3m

Are they different molecules, constitutional isomers or identical? 

Example: How are the following two compounds related?

2m

Is there a choice we can rule out immediately? 

Example: How are the following two compounds related?

4m

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

Constitutional Isomers Additional Practice Problems

How many constitutional isomers are there with molecular formula C 3H6Br2?

A. 1

B. 2

C. 3

D. 4

E. 5

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Draw all constitutional isomers that result from the monochlorination of 3-methylpentane. Do not duplicate.

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Bromocyclobutane is an achiral molecule. Draw 4 chiral cyclic constitutional isomers of this molecule in the boxes provided. Make sure to place your answers in the correct boxes such that the sterochemical relationships between the molecules in your answers are as noted.

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True or False: The following 2 compounds are constitutional isomers of each other.

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Draw a constitutional isomer of the compound given below

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How many constitutional isomers having molecular formula  C7H16 contain  at least (1) quaternary (4°) carbon atom within the structure of the molecule?

A. 0 

B. 1

C. 2

D. 3

E. 4

F. 5

G. 6

H. 7

I. 8

J. 9

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How many constitutional isomers having molecular formula   C7H16 contain  exactly two (2)  primary (1°) carbon atoms within the structure of the molecule?

A. 0 

B. 1

C. 2

D. 3

E. 4

F. 5

G. 6

H. 7

I. 8

J. 9

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Draw structural formulas for 5 (and only 5) constitutional isomers that  have one (and only one) ring and that one ring must be a three-membered ring and the molecular formula C5H7F. Your structural formulas must have no nonzero formal charges and the most typical arrangements of bonding and nonbonding valence electrons. Note that if you give the same isomer more than once, points will be deducted for that isomer. If you give more than 5 constitutional isomers, points will be deducted. For this problem, you must give complete structural formulas showing all atoms and bonding valence electrons. Do not give condensed structural formulas or bond-line formulas.

 

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Choose the compound pair that are not constitutional isomers:

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Draw structural formulas for 5 constitutional isomers that have one (and only one) three-membered ring and the molecular formula C6H12. Yes, each of the constitutional isomers that you give must be a substituted cyclopropane. Your structural formulas must have no nonzero formal charges and the most typical arrangements of bonding and nonbonding valence electrons.

Note: For this problem, you must give complete structural formulas showing all atoms and bonding valence electrons. Do not give condensed structural formulas or bond-line formulas. 

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