Question:
Among the following, the compound having conjugated double bonds is
Among the following, the compound having conjugated double bonds is
Show Hint
To identify a conjugated diene quickly, look for the pattern
\[
C=C-C=C
\]
i.e., the two double bonds must be separated by exactly one single bond.
Updated On: Jun 21, 2026
- hepta-1,6-diene
- hepta-1,3-diene
- hepta-1,4-diene
- hepta-1,5-diene
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The Correct Option is B
Solution and Explanation
Concept:
Dienes are hydrocarbons containing two carbon-carbon double bonds. Depending upon the relative positions of the double bonds, dienes are classified into three categories:
• Conjugated dienes: Double bonds are separated by one single bond. \[ C=C-C=C \]
• Isolated dienes: Double bonds are separated by two or more single bonds. \[ C=C-C-C=C \]
• Cumulated dienes: Two double bonds share a common carbon atom. \[ C=C=C \]
Conjugated dienes are particularly stable because the \(\pi\)-electrons are delocalized over four carbon atoms.
Step 1: Examine hepta-1,6-diene. Structure: \[ CH_2=CH-CH_2-CH_2-CH_2-CH=CH_2 \] The two double bonds are separated by four single bonds. Therefore, it is an isolated diene and not a conjugated diene.
Step 2: Examine hepta-1,3-diene. Structure: \[ CH_2=CH-CH=CH-CH_2-CH_2-CH_3 \] The double bonds are separated by exactly one single bond. \[ C=C-C=C \] This is the characteristic arrangement of a conjugated diene. Therefore, hepta-1,3-diene contains conjugated double bonds.
Step 3: Examine hepta-1,4-diene. Structure: \[ CH_2=CH-CH_2-CH=CH-CH_2-CH_3 \] The double bonds are separated by two single bonds. Hence it is an isolated diene.
Step 4: Examine hepta-1,5-diene. Structure: \[ CH_2=CH-CH_2-CH_2-CH=CH-CH_3 \] Again, the double bonds are separated by more than one single bond. Therefore, it is also an isolated diene.
Step 5: Conclusion. Only hepta-1,3-diene possesses the arrangement \[ C=C-C=C \] which represents conjugation. Hence the correct answer is \[ \boxed{\text{hepta-1,3-diene}} \]
• Conjugated dienes: Double bonds are separated by one single bond. \[ C=C-C=C \]
• Isolated dienes: Double bonds are separated by two or more single bonds. \[ C=C-C-C=C \]
• Cumulated dienes: Two double bonds share a common carbon atom. \[ C=C=C \]
Conjugated dienes are particularly stable because the \(\pi\)-electrons are delocalized over four carbon atoms.
Step 1: Examine hepta-1,6-diene. Structure: \[ CH_2=CH-CH_2-CH_2-CH_2-CH=CH_2 \] The two double bonds are separated by four single bonds. Therefore, it is an isolated diene and not a conjugated diene.
Step 2: Examine hepta-1,3-diene. Structure: \[ CH_2=CH-CH=CH-CH_2-CH_2-CH_3 \] The double bonds are separated by exactly one single bond. \[ C=C-C=C \] This is the characteristic arrangement of a conjugated diene. Therefore, hepta-1,3-diene contains conjugated double bonds.
Step 3: Examine hepta-1,4-diene. Structure: \[ CH_2=CH-CH_2-CH=CH-CH_2-CH_3 \] The double bonds are separated by two single bonds. Hence it is an isolated diene.
Step 4: Examine hepta-1,5-diene. Structure: \[ CH_2=CH-CH_2-CH_2-CH=CH-CH_3 \] Again, the double bonds are separated by more than one single bond. Therefore, it is also an isolated diene.
Step 5: Conclusion. Only hepta-1,3-diene possesses the arrangement \[ C=C-C=C \] which represents conjugation. Hence the correct answer is \[ \boxed{\text{hepta-1,3-diene}} \]
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