Question 1

Which sequence of reactions would best prepare the compound shown below, starting from cyclopentane?

$$\ce{\underset{cyclopentane}{C5H10} \xrightarrow{?} \underset{product}{}}

($$Refer to the images provided for the correct sequence.)

Accepted Answer

Addition of $$\ce{HBr}$$, elimination with $$\ce{t-BuO^-}$$, allylic bromination with NBS/peroxide, and methylation with $$\ce{CH3O^-}.$$

Question 2

In the free radical bromination of 1,3-dimethylcyclohexane, which product is expected to be the major product and why?

$$\ce{1,3-dimethylcyclohexane + Br2 \xrightarrow{\Delta} ?}$$

Accepted Answer

Bromination occurs at the tertiary carbon, forming the most stable tertiary radical intermediate.

Question 3

Which two different alkenes would undergo allylic bromination with NBS to produce the following product?

$$\ce{NBS, \Delta}

($$Refer to the images provided for the correct alkene structures.)

Accepted Answer

The two alkenes are (1) 1-isopropyl-2-methylcyclopentene and (2) 1-isopropyl-3-methylcyclopentene.

Question 4

Which statement best describes the role of transition states in E2 reactions?

Accepted Answer

Transition states are crucial for understanding the stereochemistry of the elimination.

Question 5

For the synthesis of 2-halopropane from propane, which halogenation method is preferred and why?

$$\ce{CH3CH2CH3 + X2 \xrightarrow{\Delta} CH3CHXCH3}$$

Accepted Answer

Bromination is preferred due to the higher selectivity of bromine.

Question 6

Which of the following mechanisms correctly depicts the first three steps in the free radical polymerization of tetrafluoroethylene using an alkoxide initiator?

$$\ce{n CF2=CF2 + RO^- \rightarrow (CF2CF2)_nOR}$$

Accepted Answer

The mechanism where the alkoxide attacks the double bond, generating a radical that propagates by adding to another monomer.

Question 7

Considering the relative stabilities of the resultant free radicals, which of the indicated carbon-halogen bonds would have a higher bond dissociation energy?

$$\ce{Cyclopentyl-Br} (a) vs$$ $$\ce{Cyclopentyl-I} (b)$$

Accepted Answer

Bond (a) would have a higher bond dissociation energy.

Question 8

Which set of reagents would you use to convert but-1-yne to 1,2-dibromobut-1-ene, 1-bromobut-1-ene, and 2-bromobut-1-ene, respectively?

$$\ce{CH3CH2C#CH \xrightarrow{?} Products}$$

Accepted Answer

Br$$_2 (1 eq) $$for 1,2-dibromobut-1-ene, HBr (1 eq) for 1-bromobut-1-ene, HBr (1 eq) with ROOR for 2-bromobut-1-ene.

Question 9

How does the transition state of bromination contribute to its selectivity compared to chlorination?

Accepted Answer

The late transition state in bromination is closer to the product, enhancing selectivity.

Question 10

Which of the following statements best explains why bromination is more selective than chlorination in free radical halogenation reactions?

Accepted Answer

Bromine radicals are less reactive and the transition state is more product-like, favoring the most stable radical.

Question 11

A student wants to synthesize 2-bromopropane from propane. Which halogen should they use and why?

Accepted Answer

They should use bromine because it is more selective for secondary hydrogens.

Question 12

Which of the following best describes the mechanism of allylic bromination using NBS?

Accepted Answer

It proceeds via a radical mechanism where bromine is introduced at the allylic position.

Question 13

Which of the following is a real-world application of free radical polymerization?

Accepted Answer

The industrial synthesis of Teflon (polytetrafluoroethylene) using tetrafluoroethylene monomers.

Question 14

Which factor most strongly influences the regioselectivity of free radical halogenation of alkanes?

Accepted Answer

The stability of the intermediate radical formed during the reaction.

Question 15

Which of the following best explains why the bond dissociation energy of a C–Br bond is higher than that of a C–I bond?

Accepted Answer

The C–Br bond is shorter and stronger due to better orbital overlap compared to the C–I bond.

Radical Reaction Synthesis from Cyclopentane

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