Mechanism 4: Bromination is a multi-step process. In this mechanism, the pi bond attacks the bromine molecule as in Mechanism 1. Some time after the carbocation is formed, the bromine atom donates a pair of electrons to form the bromonium ion. This step is slow because a strained 3-member ring is formed, and this gives time for bond rotation around the C-C bond before forming the 3-member ring, as shown. This means that two different bromonium ions are formed, leading to a mixture of products-both the meso compound and the pair of enantiomers will be formed. Br-Br OBr Br Br H Ph Ph slow Ph fast (meso) H. Br H H. Ph Ph Ph e H. H. С-С bond rotation Ph Br Br Br OBr Ph (racemic) Ph Ph slow Phy. Ph fast H H. H H H. Br H.
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.
Which isomer(s) of stilbene dibromide would be formed if the reaction followed Mechanism 4?
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