In the first step of hydroboration mechanism, why is an arrow drawn from the pi bond of the alkene to the B atom of the borane r
eagent signifying the pi electrons are used to make a new C-B bond?
1 answer:
Answer:
To fulfill octet of B atom in borane, nucleophilic attack by pi electrons of alkene takes place with electrophilic B center in borane.
Explanation:
In Borane (), B atom has energetically vacant 2p orbital and thereby octet is incomplete.Therefore B center in borane act as an electrophilic center.
In alkene, pi bonding electrons are loosely bound together due to side on overlap of two constituent p-orbitals. Hence this pi bond can be easily broken. Alternatively, we can say that pi bond in alkene act as a potential nucleophile.
The first step of hydroboration occurs in a concerted manner where pi electrons of alkene first attack vacant 2p orbital of B in borane to fulfill it's octet (represented by an arrow drawn from alkene to B atom) and forms a 4 memebered cyclic intermediate. Simulaneously, a B-H bond in borane is donated to alkene through 3c-2e bond (3 center-2 electron bond).
Full mechanism has been shown below.
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The product of the reaction of excess benzene with dichloromethane is diphenylmethane.
The reaction that benzene undergoes with dichloromethane is a Friedel-Crafts Alkylation, in which firstly Benzene is alkylated to Benzyl Chloride, and after that, the Benzyl Chloride reacts with another equivalent of Benzene to form the compound Diphenylmethane. The Reaction Scheme is shown in the image below:
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The product of the reaction of excess benzene with dichloromethane is diphenylmethane.
The reaction that benzene undergoes with dichloromethane is a Friedel-Crafts Alkylation, in which firstly Benzene is alkylated to Benzyl Chloride, and after that, the Benzyl Chloride reacts with another equivalent of Benzene to form the compound Diphenylmethane. The Reaction Scheme is shown in the image below:
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