Free Alkyl Halides MCQs with Answers
458 Alkyl Halides MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Alkyl halides are named and related to their carbon-halogen structure, polarity and reactivity. The key reactions are nucleophilic substitution by SN1 and SN2 mechanisms and elimination by E1 and E2 mechanisms, including how substrate structure, nucleophile, base, solvent and temperature influence substitution versus elimination.
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- A. a partial positive charge, since the halogen is more electronegative
- B. a partial negative charge
- C. a full negative charge
- D. no charge at all
Explanation: The carbon to halogen bond is polar, with electron density drawn towards the halogen, so the carbon is electron deficient and attracts…
Correct answer: a partial positive charge, since the halogen is more electronegative- A. a primary alkyl halide
- B. a secondary alkyl halide
- C. a tertiary alkyl halide
- D. an aryl halide
Explanation: The carbon carrying the bromine is attached to three other carbon atoms, which makes it tertiary, whereas a primary carbon is attached to…
Correct answer: a tertiary alkyl halide- A. R-F greater than R-Cl greater than R-Br greater than R-I
- B. R-I greater than R-Br greater than R-Cl greater than R-F
- C. all four react at the same rate
- D. R-Cl greater than R-I greater than R-Br greater than R-F
Explanation: Reactivity is governed by the strength of the carbon to halogen bond, and that bond weakens down the group as the halogen gets larger, so…
Correct answer: R-I greater than R-Br greater than R-Cl greater than R-F- A. ethene
- B. ethanoic acid
- C. ethane
- D. ethanol
Explanation: In aqueous solution the hydroxide ion acts as a nucleophile, replacing the bromine to give ethanol in a substitution reaction.
Correct answer: ethanol- A. a two step mechanism through a carbocation
- B. first order kinetics involving only the alkyl halide
- C. a single step in which the nucleophile attacks as the leaving group departs, with second order kinetics
- D. the formation of a free radical intermediate
Explanation: The nucleophile approaches from the side opposite the leaving group and bond forming and bond breaking occur together through a five…
Correct answer: a single step in which the nucleophile attacks as the leaving group departs, with second order kinetics- A. the tertiary carbocation formed is relatively stable and the carbon is too hindered for back side attack
- B. tertiary halides have the weakest carbon to halogen bond
- C. tertiary carbon atoms carry a full positive charge already
- D. the nucleophile is always weak
Explanation: Three electron releasing alkyl groups spread the positive charge and stabilise the carbocation, so the slow ionisation step becomes…
Correct answer: the tertiary carbocation formed is relatively stable and the carbon is too hindered for back side attack- A. both the alkyl halide and the nucleophile
- B. the alkyl halide only
- C. the nucleophile only
- D. the solvent only
Explanation: The slow, rate determining step is the ionisation of the alkyl halide into a carbocation and a halide ion, and the nucleophile is not…
Correct answer: the alkyl halide only- A. an alcohol
- B. an alkane
- C. a carboxylic acid
- D. an alkene, by elimination of hydrogen halide
Explanation: In ethanol the hydroxide ion acts as a base rather than as a nucleophile, removing a hydrogen from the carbon next to the one bearing the…
Correct answer: an alkene, by elimination of hydrogen halide- A. the less substituted, less stable alkene
- B. always the cis isomer
- C. the more highly substituted and therefore more stable alkene
- D. an alkane
Explanation: When more than one alkene can form, the preferred product is the one with the greater number of alkyl groups attached to the doubly bonded…
Correct answer: the more highly substituted and therefore more stable alkene- A. a high concentration of a strong base, a non aqueous solvent and a higher temperature
- B. dilute aqueous conditions at room temperature
- C. the use of a weak nucleophile in water
- D. cooling the mixture in ice
Explanation: Elimination has the higher activation energy and produces more particles, so heat and a strong base in ethanol push the reaction that way…
Correct answer: a high concentration of a strong base, a non aqueous solvent and a higher temperature- A. ethanol
- B. ethylamine
- C. ethanenitrile
- D. ethane
Explanation: Ammonia has a lone pair on nitrogen and acts as a nucleophile, displacing bromide to give ethylamine, though the product is itself…
Correct answer: ethylamine- A. shortens the carbon chain by one atom
- B. produces an alkene
- C. lengthens the carbon chain by one carbon atom
- D. removes the halogen without adding anything
Explanation: The cyanide ion substitutes for the halogen, so the nitrile formed has one more carbon than the starting halide, and that nitrile can then…
Correct answer: lengthens the carbon chain by one carbon atom- A. sodium metal in dry ether
- B. magnesium in dry ether
- C. zinc in aqueous solution
- D. copper in ethanol
Explanation: Magnesium inserts itself into the carbon to halogen bond to give an alkylmagnesium halide, and the ether must be perfectly dry because…
Correct answer: magnesium in dry ether- A. they contain hydrogen bonds
- B. they are ionic
- C. their molecules are lighter
- D. they are polar and have greater molar mass, so intermolecular forces are stronger
Explanation: The polar carbon to halogen bond adds dipole to dipole attraction on top of the dispersion forces, and the heavy halogen atom increases…
Correct answer: they are polar and have greater molar mass, so intermolecular forces are stronger- A. CH3Br
- B. CH3CH2Br
- C. (CH3)2CHBr
- D. (CH3)3CBr
Explanation: SN1 rates follow the stability of the carbocation formed, and that increases from primary through secondary to tertiary because each alkyl…
Correct answer: (CH3)3CBr- A. inverted, because the nucleophile attacks from the side opposite the leaving group
- B. retained completely
- C. randomised, giving a racemic mixture
- D. unchanged because no bond is broken
Explanation: Back side attack turns the three remaining groups inside out like an umbrella in the wind, so an optically active substrate gives a…
Correct answer: inverted, because the nucleophile attacks from the side opposite the leaving group- A. 1-chlorobutane
- B. 2-chlorobutane
- C. 3-chlorobutane
- D. 2-chloropropane
Explanation: The longest chain has four carbons, giving butane, and numbering from the end that puts the chlorine on the lower numbered carbon makes it…
Correct answer: 2-chlorobutane- A. the benzene ring repels all nucleophiles equally
- B. chlorine is not electronegative in aromatic compounds
- C. a lone pair on the halogen is delocalised into the ring, giving the carbon to halogen bond partial double bond character
- D. aryl halides are ionic
Explanation: Overlap between the halogen lone pair and the ring pi system shortens and strengthens the bond, so the halogen is a much poorer leaving…
Correct answer: a lone pair on the halogen is delocalised into the ring, giving the carbon to halogen bond partial double bond character- A. measure the boiling point of the halide
- B. convert the halide into an alkene
- C. prepare a Grignard reagent
- D. compare the relative rates at which different carbon to halogen bonds break
Explanation: The halide ion must be released before it can precipitate with silver, so the speed at which the precipitate appears reflects how easily…
Correct answer: compare the relative rates at which different carbon to halogen bonds break- A. dissolve ozone directly
- B. release chlorine radicals under ultraviolet light, and each radical destroys many ozone molecules in a chain reaction
- C. react with oxygen to form carbon dioxide
- D. absorb all incoming ultraviolet radiation harmlessly
Explanation: Ultraviolet light breaks the carbon to chlorine bond homolytically, and the chlorine radical produced converts ozone to oxygen and is then…
Correct answer: release chlorine radicals under ultraviolet light, and each radical destroys many ozone molecules in a chain reactionAlkyl Halides MCQs: common questions
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