Final answer:
The stability of conjugated dienes depends on their degree of conjugation. 1,3-butadiene is the most stable due to full delocalization of electrons across the double bonds. The stability decreases with increasing number of methylene groups between the double bonds, ranking 1,4-pentadiene, 1,5-hexadiene, and 1,6-heptadiene in descending order of stability.
Step-by-step explanation:
The stability of conjugated dienes can often be related to the degree of conjugation in the molecule. Conjugation refers to the alternating double and single bonds that allow for delocalization of π electrons over several adjacent atoms, increasing the stability of the molecule.
1,3-butadiene (CH2=CH-CH=CH2) is the most stable diene among the ones listed because the entire molecule is conjugated, with two double bonds separated by a single bond, allowing for full delocalization of electrons. This structure is typically more stable than isolated double bonds or those separated by more than one single bond due to the increased delocalization of electrons.
Following the stability trend based on the extent of conjugation, 1,4-pentadiene and 1,5-hexadiene have less stability since they feature less overall conjugation with each having an additional methylene group (-CH2-) between the double bonds. Finally, 1,6-heptadiene would be the least stable based on this trend because it has the most methylene groups between the double bonds, reducing the extent of conjugation and therefore, the electronic delocalization.
In ranking the stability of these conjugated dienes, the order from most to least stable would be:
- 1,3-butadiene
- 1,4-pentadiene
- 1,5-hexadiene
- 1,6-heptadien