3. Consider the following statements in reference to Sy1, S,2, E1 and E2 reactio

Question

3. Consider the following statements in reference to Sy1, S,2, E1 and E2 reactions of haloalkanes. To which mechanism(s) does each statement apply? a) Involves a carbocation intermediate b) Is first order in haloalkane and first order in nucleophile (base). c) Involves inversion of configuration at the site of substitution. d) Involves retention of configuration at the site of substitution f) Is first order in haloalkane and zero order in nucleophile (base). g) Is greatly accelerated in protic solvents of increasing polarity h) Rearrangements are common. i) Order of reactivity of haloalkanes is 3° > 2°>1°. j) Order of reactivity of haloalkanes is 1°>2° > 3°.

Explanation / Answer

a)

SN1 and E1 mechanisms involve carbocation intermediate.

b)

SN2 and E2 mechanisms are first order in haloalkane and first order in nucleophile (base).

c)

Since nucleophile attacks from the opposite end, SN2 mechanism involves inversion of configuration at the site of substitution.

d)

SN1 mechanism at a stereocenter will give predominantly a racemic product; could involve inversion as well as retention.

e)

SN1 mechanism at a stereocenter will give predominantly a racemic product.

f)

SN1 and E1 mechanisms are first order in haloalkane and zero order in nucleophile (base).

g)

Formation of carbocation is greatly accelerated in protic solvents.

SN1 and E1 mechanisms are favored.

h)

SN1 and E1 mechanisms involve carbocation rearrangement.

i)

SN1 and E1 mechanisms involving more stable carbocation follow order of haloalkane reactivity as 3° > 2° > 1°

j)

SN2 and E2 mechanisms are favored at unhindered carbon centers. They follow order of haloalkane reactivity as 1° > 2° > 3°

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