Reactions of Alkenes and Alkynes - What are the Mechanisms of Electrophilic Addition to Alkenes?

14 important questions on Reactions of Alkenes and Alkynes - What are the Mechanisms of Electrophilic Addition to Alkenes?

Name three types of addition reactions to alkenes.

1. addition of hydrogen halides (HCl, HBr and HI)
2. addition of water
3. addition of halogens(Cl2, Br2)

What is a regioselective reaction?

A regioselective reaction is a reaction in which the bond formation and bond breaking happens in one direction.

What is the Markovnikov's rule?

When HX or H2O is added to an alkene the hydrogen will add to the carbon of the double bond with the greater number of hydrogens.
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What is the rate determining step in the electrophilic addition of HCl to 2-Butene?

The addition of a proton to 2-Butene is rate determining. A carbocation and a chlorite ion are formed.

What is the second step in the addition of HCl to 2-Butene?

The two ions will react to form a new covalent bond.

What does the spacial arrangement of a carbocation look like?

According to VSEPR a carbocation is planar and has bond angles of approximately 120o.

How is the stability of carbocations ordered?

the greater the number of carbons surrounding the carbocation the greater the stability.

What is the relation between the Markovnikov's rule and carbocation stability?

The relative stabilities of the carbocations are the underlying basis of the Markovnikov's rule.

How does the inductive effect account for the relative stabilities of the carbocations?

Through the inductive effect the positive charge is delocalized. The delocalization is greater when there are more carbon atoms bounded to the cation.

What are the steps in acid catalyzed hydration of Propene?

1. The addition of a proton to the double bond.
2. Reaction between a nucleophile and electrophile to form a new covalent bond.
3. Removal of a proton from the H2O group.

What is a stereoselective reaction?

In a stereoselective reaction only one of all possible stereoisomers is formed or destroyed.

What is meant with anti stereoselectivity?

Anti stereoselectivity means that the addition of atoms happens on opposite sites of a carbon-carbon double bond.

Describe the mechanism of bromine addition to a carbon-carbon double bond.

1. The bromine serves as an electrophile creating a bridged bromonium ion intermediate and a bromide ion.
2. The bromide ion serves as a nucleophile and reacts with the bromonium ion.

What is a halonium ion?

A halonium ion is an ion in which the halogen bears the positive charge.

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