[mana]

hi all
 which one ( A, B or C) react faster respectively with maleic anhydride ?
I know steric effect is dominant here but I can't understand why C is the fastest and then A and B

[Enthalpy]

A drawing on a flat papersheet or screen does not represent all the shapes a molecule can take.

[wildfyr]

Think about other forms A and B can take that C cannot.

[mana]

yes that's right 
2,3-ditersiobutyl 1,3-butadiene (B) is not s-cis as mentioned in the figure and it must be s-trans because of steric hindered  so it doesn't react with maleic anhydride but what about A?

[wildfyr]

The question is about reaction speed, they can all react to one degree or another.

Both A and B can be cis or trans, however, which form do you think they prefer? And can they interconvert?

Is C cis or trans? Can it interconvert?

[mana]

you mean C can not interconvert because it is a ring and the inter conversion makes it very unstable so it is impossible, B also just prefer s-trans so it can not react at all,, but A is average it can have both s- trans and s-cis configuration so the trend is:
C > A > B
am I right?