Question

Which of the following is not a cumulated diene?

• A. Hexa-1,2-diene
• B. Hexa-2,3-diene
• C. Penta-2,3-diene
• D. Penta-1,3-diene

Answer 1

The correct option is D

Penta-1,3-diene

Explanation for correct option:

D. Penta-1,3-diene

Cumulated diene:

• “Cumulated dienes are the two double bonds connected to similar carbon atoms.”
• Cumulated dienes are low in stability as compared to other alkenes.
• Cumulated diene has two continuous double bonds $\mathrm{C}=\mathrm{C}=\mathrm{C}$ structure.
• Penta-1,3-diene is not a cumulated diene as it doesn't have continuous double bonds.
• The structure of Penta-1,3-diene is given below:

${\mathrm{CH}}_2=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-{\mathrm{CH}}_3$
Explanation for incorrect options:

A. Hexa-1,2-diene

• It is a cumlated diene. The structure is shown below:

${\mathrm{CH}}_2=\mathrm{C}=\mathrm{CH}-{\mathrm{CH}}_2-{\mathrm{CH}}_2-{\mathrm{CH}}_3$

B. Hexa-2,3-diene

• It is a cumlated diene. The structure is shown below:
• ${\mathrm{CH}}_3-\mathrm{CH}=\mathrm{C}=\mathrm{CH}-{\mathrm{CH}}_2-{\mathrm{CH}}_3$

C. Penta-2,3-diene

• It is a cumlated diene. The structure is shown below:

${\mathrm{CH}}_3-\mathrm{CH}=\mathrm{C}=\mathrm{CH}-{\mathrm{CH}}_3$

Hence, the correct option is D i.e. Penta-1,3-diene.