Consider the following Diels-Alder reaction: a) Draw a detailed mechanism for the reaction and show the structures of the endo and exo products. b) Label the endo and exo product in part a. c) Which transition state is lower in energy, the one leading to the exo product or the one leading to the endo product?
Reactive Intermediates
In chemistry, reactive intermediates are termed as short-lived, highly reactive atoms with high energy. They rapidly transform into stable particles during a chemical reaction. In specific cases, by means of matrix isolation and at low-temperature reactive intermediates can be isolated.
Hydride Shift
A hydride shift is a rearrangement of a hydrogen atom in a carbocation that occurs to make the molecule more stable. In organic chemistry, rearrangement of the carbocation is very easily seen. This rearrangement can be because of the movement of a carbocation to attain stability in the compound. Such structural reorganization movement is called a shift within molecules. After the shifting of carbocation over the different carbon then they form structural isomers of the previous existing molecule.
Vinylic Carbocation
A carbocation where the positive charge is on the alkene carbon is known as the vinyl carbocation or vinyl cation. The empirical formula for vinyl cation is C2H3+. In the vinyl carbocation, the positive charge is on the carbon atom with the double bond therefore it is sp hybridized. It is known to be a part of various reactions, for example, electrophilic addition of alkynes and solvolysis as well. It plays the role of a reactive intermediate in these reactions.
Cycloheptatrienyl Cation
It is an aromatic carbocation having a general formula, [C7 H7]+. It is also known as the aromatic tropylium ion. Its name is derived from the molecule tropine, which is a seven membered carbon atom ring. Cycloheptatriene or tropylidene was first synthesized from tropine.
Stability of Vinyl Carbocation
Carbocations are positively charged carbon atoms. It is also known as a carbonium ion.
a) Draw a detailed mechanism for the reaction and show the structures of the endo and exo products.
b) Label the endo and exo product in part a.
c) Which transition state is lower in energy, the one leading to the exo product or the one leading to the endo product?
d) Which product do you expect to be more stable (the exo or the endo product) and why?
Using your answers to part c and d, draw the reaction co-ordinate diagram for the Diels-Alder reaction shown above. Which product do you expect to be favored at high temperatures, and which product at low temperatures (which product is the kinetic product and which one the
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