Question 1

Which of the following statements best explains why the tert-butylcyclohexane (structure labeled '1') produces the fewest unique monobrominated products upon radical bromination with N-bromosuccinimide (NBS) and UV light?

Accepted Answer

The tert-butyl group creates symmetry, making multiple allylic hydrogens equivalent and reducing the number of unique products.

Question 2

Given the structures shown, which compound (by its number label) would you expect to yield the greatest number of unique monobrominated products after radical bromination with NBS and UV light?

Accepted Answer

Compound 4 (methylcyclohexene)

Question 3

Why does methylcyclohexene (structure labeled '4') produce more unique monobrominated products than cyclohexene (structure labeled '2') when treated with NBS and UV light?

Accepted Answer

The methyl group introduces additional non-equivalent allylic positions for bromination.

Question 4

Which position is most likely to be brominated in styrene (structure labeled '3') under NBS/UV conditions?

Accepted Answer

The benzylic position adjacent to the aromatic ring.

Question 5

If cyclohexene (structure labeled '2') is treated with NBS and UV light, which type of hydrogen is selectively abstracted to form the monobrominated product?

Accepted Answer

Allylic hydrogen

Question 6

Which of the following best describes the selectivity of NBS/UV radical bromination in the context of the compounds shown?

Accepted Answer

It selectively brominates allylic and benzylic positions due to resonance stabilization of the radical.

Question 7

A student proposes that cyclohexene (structure '2') and styrene (structure '3') will yield the same number of unique monobrominated products after NBS/UV bromination. Is this correct? Why or why not?

Accepted Answer

No, because styrene has a benzylic position while cyclohexene has allylic positions, leading to different numbers of unique products.

Question 8

Which compound would produce only one unique monobrominated product under NBS/UV conditions due to its symmetry?

Accepted Answer

tert-butylcyclohexane (structure '1')

Question 9

If a chemist wants to maximize the number of unique monobrominated products from an allylic bromination, which structural feature should they introduce to a cyclohexene ring?

Accepted Answer

Add a methyl group to break symmetry and create more unique allylic positions.

Question 10

Which of the following is the correct ranking (from fewest to most) for the number of unique monobrominated products formed by NBS/UV bromination of the compounds shown?

Accepted Answer

1 (tert-butylcyclohexane), 2 (cyclohexene), 3 (styrene), 4 (methylcyclohexene)

Question 11

Which of the following best explains why NBS is used instead of Br$$_2$$ for allylic bromination?

Accepted Answer

NBS provides a low, steady concentration of Br$$_2 to $$favor allylic bromination over addition to the double bond.

Question 12

In the context of radical bromination, what is the major reason for the formation of multiple unique products in methylcyclohexene (structure '4')?

Accepted Answer

The methyl group creates non-equivalent allylic positions, increasing the number of possible products.

Question 13

Which of the following is a common misconception about NBS/UV bromination of cyclohexene?

Accepted Answer

That bromination occurs at the vinylic position rather than the allylic position.

Question 14

A student claims that the number of unique monobrominated products for a given compound is always equal to the number of unique hydrogen environments. Is this always true for NBS/UV bromination?

Accepted Answer

No, because only allylic or benzylic hydrogens are brominated, not all unique hydrogen environments.

Radical Bromination with NBS: Predicting Monobrominated Products

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