19hhmmmm................... none interested in organic ????? simple compbination of organic and physical chemistry laws are applicable here!!!
we know that butadiene mainly exists in the s- trans conformation as it is the more stable form. how then is diels alder reaction involving butadiene as the dienophile is mainly possible using s-cis conformation of the butadiene substrate??
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6 Answers
19
3the rotational barrier is small in case of s trans butadiene bcos we have no bulky gps, so we can easily convert this into s-cis form by giving a small energy.
24s-trans confirmation is more stable due to less steric strain(bigger groups far apart)
but in diels alder reaction s-trans unable to react becoz carbon C1 and C4 are too far apart to bond simultaneously to the dienophile
=> s-cis form only reacts [1]
19i will give you the answer ; it is a bit confusing but still quite compact:
There is very little s-cis( this means cisoid form i.e. both double bonds on one side of the single bond) form of butadiene but it is enough to let the reaction happen. Once the reaction starts , the equilibrium between s-cis and s-trans forms ,shifts towards s-cis form following le-chatelier's principle. eventually all diene molecules are converted to product!