Question

Alkyl halides undergo ____________ reactions with nucleophiles. Strong nucleophiles favor the ____________ mechanism over the ____________ mechanism. An SN1 mechanism forms a ____________ as a reactive intermediate and the mechanism has ____________ . Protic solvents favor ____________ mechanism and aprotic solvents favor the ____________ . ____________ reactions proceed with racemization at a single stereogenic center. Increasing alkyl substitution favors an ____________ mechanism while decreasing alkyl substitution favors an ____________ mechanism. A ____________ is a positively charged carbon atom.

Answer 1

Answer:

Alkyl halides undergo nucleophilic substitution reactions with nucleophiles. Strong nucleophiles favor the SN2 mechanism over the SN1  mechanism. An SN1 mechanism forms a carbocation as a reactive intermediate and the mechanism has two steps (first order) . Protic solvents favor SN1 mechanism and aprotic solvents favor the SN2 . SN1 reactions proceed with racemization at a single stereogenic center. Increasing alkyl substitution favors an SN1 mechanism while decreasing alkyl substitution favors an SN2 mechanism. A carbocation is a positively charged carbon atom.

Explanation:

1) Alkyl halides undergo nucleophilic substitution reactions with nucleophiles: the halide ion is being substituted by another nucleophile. It may follow SN1 or SN2 mechanism.

2) Strong nucleophiles favor the SN2 mechanism over the SN1  mechanism: The nucleophile attacks from back side on the halide substituted carbon and at the same time the halide gets removed. So the rate of reaction in SN2 depends upon concentration of both alkyl halide and nucleophile.

3) An SN1 mechanism forms a carbocation as a reactive intermediate and the mechanism has two steps (first order) : there are two step in SN1, the first step is rate determining step and it leads to formation of carbocation. more the stable carbocation more the rate of reaction. The second step is fast step and it involves attack of nulceophile on the carbocation.

4)  Protic solvents favor SN1 mechanism and aprotic solvents favor the SN2

In SN1 we need to separate the carbocation with the halide ion so the SN1 reactions are favored by protic solvents

5) SN1 reactions proceed with racemization at a single stereogenic center: The first step forms a trigonal planar carbocation and the nucleophile is free to attack on the carbocation from either side causing racemization.

6) The Increasing alkyl substitution favors an SN1 mechanism while decreasing alkyl substitution favors an SN2 mechanism. A carbocation is a positively charged carbon atom.: In SN1 there is formation of carbocation which following the following order for stability

tertiary > secondary> primary

Thus more the stable carbocation more the rate of SN1 reaction.

In case of SN2 tertiary alkyl halide show hindrance for attack by nucleophile