Orgo Q

[nixon13]

View attachment Orgo Rxn.bmp


My question is how do u know where the double bond will add? Why is it different for these two rxns? This is also on Roadmap 3 DAT Destroyer.

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[dnascramble]

(CH3)3CO-Na+is bulky so it will take H+ from less substitued carbon.

 

[nixon13]

which carbon is that?

 

[klutzy1987]

A small base can get inside the ring and make a double bond in the more stable position (zaitchev). However due to steric hinderance a large bulky base like T-Butoxide will not be able to get into the ring and will make the double bond in the most sterically unhindered position (hoffman).

 

[PooyaH]

which carbon is that?

In the first one you have a strong bulky base and when #2 occurs, the double bond forms with the side that has a less substituted carbon in this case the CH3 on the top of the ring.

In the second one you have a strong base which is not bulky so it would do the opposite and form a double bond with the side that has a more substituted carbon in this case with the adjacent carbon on the right side.

 

[dnascramble]

(CH3)3CO-takes H+ from CH3- group and C2H5O- takes H+ from -CH2- to form adouble bond

 

[nixon13]

So in elimination, big bulky bases will follow hoffmans where as a smaller base will follow zaitsev?

 

[osimsDDS]

bulky bases (tertiary bases) will add the double bond to the less substituted Carbon while a normal strong base (primary) will add the doble bond to the most substituted C