30 exam-style questions on Chemistry · Alkyl halides, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Ten Chemistry · Alkyl halides questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. An optically active tertiary alkyl halide is hydrolysed by the SN1 mechanism and the product is largely racemic. This is because
A
the planar carbocation can be attacked from either face
B
the nucleophile always attacks from the side opposite the halogen
C
the reaction is a single step with no intermediate
D
the carbocation keeps the pyramidal shape of the halide
Show answer
Answer: A. In SN1 the C–X bond breaks first, giving a planar, sp2 carbocation that the nucleophile can bond to from either face with nearly equal chance, forming both enantiomers. One-step back-side attack describes SN2, which gives inversion.
2. Which of these haloethanes has the highest boiling point?
A
CH3CH2Br
B
CH3CH2Cl
C
CH3CH2F
D
CH3CH2I
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Answer: D. For the same alkyl group, the boiling point rises from F to I because the larger, heavier and more polarisable halogen gives stronger London forces. The greater polarity of the C–F bond does not outweigh this, so fluoroethane boils lowest.
3. Which alkyl bromide reacts fastest with OH− by the SN2 mechanism?
A
CH3Br
B
CH3CH2Br
C
(CH3)2CHBr
D
(CH3)3CBr
Show answer
Answer: A. The nucleophile must reach the back of the carbon bearing Br, so the least crowded carbon reacts fastest: methyl > primary > secondary > tertiary. (CH3)3CBr reacts fastest by SN1, not SN2.
4. SN1 hydrolysis of an optically active alkyl halide gives an alcohol that is 60% of the inverted configuration and 40% of the retained configuration. The product is best described as
A
fully racemised, with no optical activity
B
completely inverted, as in SN2
C
partly racemised, with excess retention
D
partly racemised, with excess inversion
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Answer: D. The 40% retained form pairs with 40% of the inverted form as a racemic mixture (80% in all), leaving a 20% excess of inversion. The excess arises because the departing halide ion briefly shields the face it leaves, so attack from the opposite side is slightly favoured.
5. For the same alkyl group, the order of reactivity of alkyl halides in nucleophilic substitution is
A
R–F > R–Cl > R–Br > R–I
B
R–I > R–Br > R–Cl > R–F
C
R–Cl > R–Br > R–I > R–F
D
R–Br > R–Cl > R–I > R–F
Show answer
Answer: B. Reactivity is controlled by the strength of the C–X bond, not its polarity: C–I is the weakest bond and breaks most easily, C–F the strongest. Ordering by electronegativity (bond polarity) gives the reverse.
6. Bromoethane is heated in a sealed tube with a large excess of ammonia in ethanol. The main organic product is
A
ethylamine, C2H5NH2
B
diethylamine, (C2H5)2NH
C
triethylamine, (C2H5)3N
D
ethanol, C2H5OH
Show answer
Answer: A. NH3 replaces Br, giving the primary amine C2H5NH2. With ammonia in large excess, each bromoethane molecule is far more likely to meet NH3 than an amine already formed, so further substitution is kept small.
7. Isobutyl chloride, (CH3)2CHCH2Cl, has the IUPAC name
A
2-chloro-2-methylpropane
B
1-chloro-2-methylpropane
C
1-chlorobutane
D
2-chlorobutane
Show answer
Answer: B. The longest chain containing the C–Cl carbon has three carbons, with Cl on C-1 and a methyl branch on C-2. 2-Chloro-2-methylpropane is tert-butyl chloride, while 1-chlorobutane and 2-chlorobutane are n-butyl and sec-butyl chloride.
8. For alkyl halides with the same halogen, the order of reactivity by the SN1 mechanism is
A
methyl > primary > secondary > tertiary
B
secondary > tertiary > primary > methyl
C
primary > secondary > tertiary > methyl
D
tertiary > secondary > primary > methyl
Show answer
Answer: D. The SN1 rate depends on forming a carbocation, which electron-releasing alkyl groups stabilise, so tertiary halides react fastest. SN2 shows the reverse order because bulky groups hinder back-side attack, and secondary halides can react by either path.
9. Which isomer of C4H9Br has the lowest boiling point?
A
1-bromobutane
B
2-bromo-2-methylpropane
C
2-bromobutane
D
1-bromo-2-methylpropane
Show answer
Answer: B. Branching makes a molecule more compact, reducing the surface over which London forces act. 2-Bromo-2-methylpropane is the most branched isomer (about 73 °C), while unbranched 1-bromobutane boils highest (about 101 °C).
10. In two hydrolysis reactions, [OH−] is doubled while the alkyl halide concentration is unchanged. By what factors do the rates change for bromomethane (SN2) and for 2-bromo-2-methylpropane (SN1)?
A
1 and 2
B
2 and 2
C
2 and 1
D
4 and 1
Show answer
Answer: C. SN2: rate = k[RX][OH−], so doubling [OH−] doubles the rate. SN1: rate = k[RX], which does not depend on [OH−], so the rate is unchanged. A factor of 4 would need [RX] doubled as well.
How many Chemistry · Alkyl halides MCQs are there?
30, each with the answer and a short explanation, across 1 topics: Alkyl halides. Every chapter test draws ten of them, so you can take it many times.
Is the MDCAT Chemistry chapter 15 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
