Question

Draw all constitutional isomers with the following molecular formula.

(a) C₃H₇Cl   

(b) C₄H₁₀ 

(c) C₅H₁₂ 

(d) C₄H₁₀O

(e) C₃H₆ Cl₂

Answer 1

Solution

The task is to draw all constitutional isomers that have the given molecular formula.

Constitutional isomers are compounds that have the same molecular formula but differ in their structural formulas.

a) The molecular formula is C${}^3$H${}^7$Cl.

First, draw a 3 carbon main chain.

Add the chlorine atom to the 1st carbon.

First, draw a 3 carbon main chain.

Add the chlorine atom to the 2nd carbon.

There are 2 constitutional isomers with the given molecular formula.

 

b) The molecular formula is C${}^4$H${}^1$${}^0$.

To solve this task it is best to work systematically, decrease the length of the main chain and draw every possible isomer.

There are 4 C in the molecular formula, so draw a 4 carbon main chain.

Decrease the main chain length and draw a 3 carbon main chain and add a methyl group.

There are 2 constitutional isomers with the given molecular formula.

 

c) The molecular formula is C${}^5$H${}^1$${}^2$.

To solve this task it is best to work systematically, decrease the length of the main chain, and draw every possible isomer.

There are 5 C in the molecular formula, so first draw a pentane.

Decrease the chain length and draw a 4 C main chain, add a methyl group.

Decrease the main chain length again, draw a 3 C main chain, add 2 methyl groups on the 2nd carbon.

There are 3 constitutional isomers with the given molecular formula.

 

d) The molecular formula is C${}^4$H${}^1$${}^0$O.

To solve this task it is best to work systematically, decrease the length of the main chain, and draw every possible isomer.

In addition to that, there are 2 kinds of compounds that contain 1 oxygen atom, alcohols and ethers.

First, draw all possible alcohols.

There are 4 C in the molecular formula, so draw a 4 C main chain and add a hydroxy group to the 1st carbon.

Draw a 4 C main chain again, but this time add the hydroxy group to the 2nd carbon.

Decrease the main chain length, draw a 3 C main chain, add a methyl group to the 2nd carbon and a hydroxy group to the 1st carbon atom.

Draw a 3 C main chain again, this time add both the methyl and the hydroxy groups to the 2nd carbon.

Now draw all possible ethers.

Draw a methoxy group first, and then add the 3 carbon long alkyl chain.

Draw the methoxy group first, and add the 3 C alkyl chain again, but this time connect the oxygen atom to the central carbon of the alkyl chain.

Draw an ethoxy group first, and then add a 2 carbon long alkyl chain.

There are 7 constitutional isomers with the given molecular formula.

 

e) The molecular formula is C${}^3$H${}^6$Cl${}^2$.

There are 3 C in the molecular formula, so draw a 3 C long main chain.

Add 2 chlorine atoms to the 1st carbon.

There are 3 C in the molecular formula, so draw a 3 C long main chain.

Add 2 chlorine atoms, 1 on the 1st carbon and 1 on the 2nd carbon.

There are 3 C in the molecular formula, so draw a 3 C long main chain.

Add 2 chlorine atoms, 1 on the 1st carbon and 1 on the 3rd carbon.

There are 3 C in the molecular formula, so draw a 3 C long main chain.

Add 2 chlorine atoms to the 2nd carbon.

There are 4 constitutional isomers with the given molecular formula.