conjugated diene stability

[spoog74]

question #209 in dat destroyer 2011 edition, it asks which diene is most stable..

Can someone explain how the answer is C and how it differs from any other figure there?

Doesnt conjugated mean sp2 hybridization all around? How is that the case when the answer contains 2 sp3 carbons?

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[LaughingGas]

question #209 in dat destroyer 2011 edition, it asks which diene is most stable..

Can someone explain how the answer is C and how it differs from any other figure there?

Doesnt conjugated mean sp2 hybridization all around? How is that the case when the answer contains 2 sp3 carbons?

A,B,E are isolated dienes.
-Conjugated dienes means double bond separated by only 1 single bond.
-Isolated dienes means double bond separated by more than 2 single bonds.
B/c the carbons of conjugated dienes(from one end of double bond to the end of other double bond) (C and D) are sp2, you can draw resonance structures, while isolated dienes (A,B,E ) , the double bonds are separated by sp3 Carbon, being unable to do resonance. That makes conjugated more stable than isolated.
Between C and D, the more substituted alkenes are more stable, which in this case its C.

 

[spoog74]

A,B,E are isolated dienes.
-Conjugated dienes means double bond separated by only 1 single bond.
-Isolated dienes means double bond separated by more than 2 single bonds.
B/c the carbons of conjugated dienes(from one end of double bond to the end of other double bond) (C and D) are sp2, you can draw resonance structures, while isolated dienes (A,B,E ) , the double bonds are separated by sp3 Carbon, being unable to do resonance. That makes conjugated more stable than isolated.
Between C and D, the more substituted alkenes are more stable, which in this case its C.

Gd bless, thank you.