Question

Question: Determine the degree of unsaturation for hydrocarbons with the following molecular formulas:

a. C₂₀H₃₄ b. C₈H₁₆ c. C₁₂H₂₀ d. C₄₀H₅₆

Short answer

We have to determine the degree of unsaturation for the following hydrocarbons:

a) Degree of unsaturation= 4

b) Degree of unsaturation= 1

c) Degree of unsaturation= 3

d) Degree of unsaturation= 13

Step-by-step solution

What is degree of unsaturation

The total number of p bonds and rings in a hydrocarbon is called degree of unsaturation.

What is p bond-

When formation of double bond or triple bond occurs then there will be the presence of p bond. In double bond there is one p bond and in triple bond there is two p bonds. p bond is formed with the help of two electrons so when p bond is formed two hydrogens will become less than the simple hydrocarbon chain.

When ring formed then also two hydrogen will become less from the simple hydrocarbon chain.

How to find

a)For a 20-carbon hydrocarbon with no p bonds and no rings, C_nH_{2n + 2} = C₂₀H₄₂. A

20-carbon compound with molecular formula C₂₀H₃₄ has eight fewer hydrogens, so the degree of unsaturation is 8/2 = 4.

b) For a 8-carbon hydrocarbon with no p bonds and no rings, C_nH_{2n + 2} = C₈H₁₈. A

20-carbon compound with molecular formula C₈H₁₆ has two fewer hydrogens, so the degree of unsaturation is 2/2 = 1.

c) For a 12-carbon hydrocarbon with no p bonds and no rings, C_nH_{2n + 2} = C₁₂H₂₆. A

20-carbon compound with molecular formula C₁₂H₂₀ has six fewer hydrogens, so the degree of unsaturation is 6/2 = 3.

d) For a 40-carbon hydrocarbon with no p bonds and no rings, C_nH_{2n + 2} = C₄₀H₈₂. A

20-carbon compound with molecular formula C₄₀H₅₆ has twenty six fewer hydrogens, so the degree of unsaturation is 26/2 = 13.