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Chapter 15: Q.8-d (page 763)

Question: When is added to buta-1,3- diene at -150C, the product mixture contains 60% of product A and 40% of product B. When the same reaction takes place at 600C, the product ratio is 10% A and 90% B.

a. Propose structures for products A and B (Hint: In many case, an allylic carbocation is more stable than a bromonium ion.)

b. Propose a mechanism to account for formation of both A and B.

c. Show why A predominates at -150C and B predominates at 600C .

d. If you had a solution of pure A, and its temperature were raised to 600C , what would you expect to happen ? Propose a mechanism to support your prediction.

Short Answer

Expert verified

Answer

d. The mechanism when pure A compound raises its temperature to 600C is given below.


Step by step solution

01

Ionization

Ionization leads to carbocation formation and is mainly expected in alkene radical cations. The nucleophile attacks that carbon which is electron deficient.

02

Mechanism of pure A when temperature raised to  600C

(d)The A’s ionization at temperature 600C results in the same allylic carbocation as shown in (b) part. It also gives the same product ratios of A and B from butadiene.

The mechanism when pure A’s temperature raised to 600C

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Most popular questions from this chapter

Question: Draw another resonance form for each of the substituted allylic cations shown in the preceding figure, showing how the positive charge is shared by another carbon atom. In each case, state whether your second resonance form is a more important or less important resonance contributor than the first structure. (Which structure places the positive charge on the more-substituted carbon atom?)

Show how you might synthesize the following compounds starting with bromobenzene, and alkyl or alkenyl halides of four carbon atoms or fewer.

a. 3-phenylprop-1-ene

b.5-methylhex-2-ene

c. dec-5-ene

Question: Predict the product(s) of light-initiated reaction with NBS in CCl4 for the following starting materials.

  1. cyclohexene
  2. 3,4-dimethylhex-3-ene

Question: When is added to buta-1,3- diene at -150C, the product mixture contains 60% of product A and 40% of product B. When the same reaction takes place at 600C, the product ratio is 10% A and 90% B.

a. Propose structures for products A and B (Hint: In many case, an allylic carbocation is more stable than a bromonium ion.)

b. Propose a mechanism to account for formation of both A and B.

c. Show why A predominates at -150C and B predominates at 600C .

d. If you had a solution of pure A, and its temperature were raised to 600C , what would you expect to happen ? Propose a mechanism to support your prediction.

Question: When Br2 is added to buta-1,3- diene at -150C , the product mixture contains 60% of product A and 40% of product B. When the same reaction takes place at -600C, the product ratio is 10% A and 90% B.

a. Propose structures for products A and B (Hint: In many case, an allylic carbocation is more stable than a bromonium ion.)

b. Propose a mechanism to account for formation of both A and B.

c. Show why A predominates at -150C and B predominates at -600C .

d. If you had a solution of pure A, and its temperature were raised to -600C , what would you expect to happen ? Propose a mechanism to support your prediction.
See all solutions

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