Degree of unsaturation: Class 11 practice
Degree of unsaturation (double-bond equivalents) = (2C + 2 + N − H − X)/2. Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Molecular formulae
The idea behind degree of unsaturation
Degree of unsaturation (double-bond equivalents) = (2C + 2 + N − H − X)/2. Each ring or double bond counts 1; a triple bond counts 2.
Step-by-step method
- Count C, H, N and halogens (X).
- Apply the formula.
- Interpret as rings + π bonds.
Worked example 1 (Basic)
Find the degree of unsaturation of C₆H₆.
- (2 × 6 + 2 + 0 − 6 − 0)/2
- = 4
- Answer: 4
Worked example 2 (Standard)
Find the degree of unsaturation of C₂H₃Cl.
- (2 × 2 + 2 + 0 − 3 − 1)/2
- = 1
- Answer: 1
Worked example 3 (Challenge)
Find the degree of unsaturation of C₅H₅N.
- (2 × 5 + 2 + 1 − 5 − 0)/2
- = 4
- Answer: 4
Common mistakes and misconceptions
- Ignoring halogens
- Counting oxygen
Practice questions
- (Basic) Find the degree of unsaturation of C₁₀H₈.
- (Basic) Find the degree of unsaturation of C₆H₁₂.
- (Standard) Find the degree of unsaturation of C₆H₅Cl.
- (Standard) Find the degree of unsaturation of C₃H₆O.
- (Challenge) Find the degree of unsaturation of C₂H₂.
- (Challenge) Find the degree of unsaturation of C₇H₈.
Answer key with full working
- Q1: (2 × 10 + 2 + 0 − 8 − 0)/2 → = 7 → Answer: 7
- Q2: (2 × 6 + 2 + 0 − 12 − 0)/2 → = 1 → Answer: 1
- Q3: (2 × 6 + 2 + 0 − 5 − 1)/2 → = 4 → Answer: 4
- Q4: (2 × 3 + 2 + 0 − 6 − 0)/2 → = 1 → Answer: 1
- Q5: (2 × 2 + 2 + 0 − 2 − 0)/2 → = 2 → Answer: 2
- Q6: (2 × 7 + 2 + 0 − 8 − 0)/2 → = 4 → Answer: 4
Syllabus note
This skill is listed under "Organic Chemistry – Basic Principles" for Class 11 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
Frequently asked questions
Which chapter is degree of unsaturation in?
"Organic Chemistry – Basic Principles", Class 11 Chemistry (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.