1-Bromobutane, CH₃CH₂CH₂CH₂Br, a primary halide, is treated with potassium tert-butoxide, KOC(CH₃)₃, in tert-butyl alcohol. Which mechanism leads?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 5. Read 2026-10-03.
1-Bromobutane, CH₃CH₂CH₂CH₂Br, a primary halide, is treated with sodium azide, NaN₃, in DMF. Which mechanism leads?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
1-Bromopentane, CH₃(CH₂)₄Br, a primary halide, is heated with potassium tert-butoxide, KOC(CH₃)₃, in tert-butyl alcohol. Which mechanism leads?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 5. Read 2026-10-03.
1-Bromopropane, CH₃CH₂CH₂Br, a primary halide, is treated with sodium iodide in acetone. Which mechanism leads?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
Show all 43 questions (39 more)
Methyl and primary, continued
1-Chloropropane, CH₃CH₂CH₂Cl, a primary halide, is treated with sodium cyanide in DMSO. Which mechanism leads?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
Bromoethane, CH₃CH₂Br, a primary halide, is treated with sodium ethanethiolate, NaSCH₂CH₃, in DMF. Which mechanism leads?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
Bromomethane, CH₃Br, a methyl halide, is treated with sodium hydroxide in water. Which mechanism leads?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
Butyl tosylate, CH₃CH₂CH₂CH₂OTs, a primary tosylate, is treated with sodium iodide in acetone. Which mechanism leads?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
Chloromethane, CH₃Cl, a methyl halide, is treated with sodium methanethiolate, NaSCH₃, in acetone. Which mechanism leads?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
Iodomethane, CH₃I, a methyl halide, is treated with sodium cyanide in DMSO. Which mechanism leads?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
Secondary 10
2-Bromobutane, CH₃CHBrCH₂CH₃, a secondary halide, is heated with potassium hydroxide in ethanol. Which mechanism leads?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Bromobutane, CH₃CHBrCH₂CH₃, a secondary halide, is treated with sodium cyanide in DMSO. Which mechanism leads?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Bromopentane, CH₃CHBrCH₂CH₂CH₃, a secondary halide, is heated with sodium ethoxide, NaOCH₂CH₃, in ethanol. Which mechanism leads?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Bromopropane, (CH₃)₂CHBr, a secondary halide, is treated with potassium tert-butoxide, KOC(CH₃)₃, in tert-butyl alcohol. Which mechanism leads?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Bromopropane, (CH₃)₂CHBr, a secondary halide, is treated with sodium azide, NaN₃, in DMF. Which mechanism leads?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Bromopropane, (CH₃)₂CHBr, a secondary halide, is treated with sodium methanethiolate, NaSCH₃, in acetone. Which mechanism leads?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Chloropentane, CH₃CHClCH₂CH₂CH₃, a secondary halide, is treated with sodium iodide in acetone. Which mechanism leads?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
Bromocyclohexane, C₆H₁₁Br, a secondary halide, is heated with sodium ethoxide, NaOCH₂CH₃, in ethanol. Which mechanism leads?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
Bromocyclopentane, C₅H₉Br, a secondary halide, is treated with sodium ethanethiolate, NaSCH₂CH₃, in DMF. Which mechanism leads?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
Isopropyl tosylate, (CH₃)₂CHOTs, a secondary tosylate, is treated with potassium tert-butoxide, KOC(CH₃)₃, in tert-butyl alcohol. Which mechanism leads?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
Tertiary 11
1-Bromo-1-methylcyclohexane, a tertiary halide (the ring carbon that holds Br also holds a CH₃), is heated with sodium methoxide, NaOCH₃, in methanol. Which mechanism leads?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
1-Bromo-1-methylcyclohexane, a tertiary halide, is heated in methanol with no base added. Some 1-methylcyclohexene forms. Which mechanism made the alkene?Answer: E1. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.2; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Bromo-2-methylbutane, (CH₃)₂CBrCH₂CH₃, a tertiary halide, is heated in water with no base added. Some 2-methyl-2-butene forms. Which mechanism made the alkene?Answer: E1. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.2; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Bromo-2-methylbutane, (CH₃)₂CBrCH₂CH₃, a tertiary halide, is treated with sodium ethoxide, NaOCH₂CH₃, in ethanol. Which mechanism leads?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Bromo-2-methylpropane, (CH₃)₃CBr, a tertiary halide, is heated with sodium hydroxide in ethanol. Which mechanism leads?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Bromo-2-methylpropane, (CH₃)₃CBr, a tertiary halide, is stirred in water at room temperature with nothing else added. It gives 2-methyl-2-propanol, (CH₃)₃COH. Which mechanism made the alcohol?Answer: SN1. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 7.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Bromo-2-methylpropane, (CH₃)₃CBr, a tertiary halide, is warmed in ethanol with no base added. Besides the ether, some 2-methylpropene, (CH₃)₂C=CH₂, forms. Which mechanism made the alkene?Answer: E1. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.2; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Bromo-2-methylpropane, (CH₃)₃CBr, is a tertiary halide. Which of the four mechanisms is shut out for it, whatever the reagent?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 7.2; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Chloro-2-methylbutane, (CH₃)₂CClCH₂CH₃, a tertiary halide, is left in ethanol at room temperature with nothing else added. It gives 2-ethoxy-2-methylbutane. Which mechanism made the ether?Answer: SN1. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 7.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Chloro-2-methylpropane, (CH₃)₃CCl, a tertiary halide, is left in methanol with nothing else added. It gives tert-butyl methyl ether, (CH₃)₃COCH₃. Which mechanism made the ether?Answer: SN1. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 7.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
2-Chloro-2-methylpropane, (CH₃)₃CCl, a tertiary halide, is treated with potassium tert-butoxide, KOC(CH₃)₃, in tert-butyl alcohol. Which mechanism leads?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
From the evidence 12
A halide is heated in ethanol with no base added and gives an alkene whose carbon skeleton differs from that of the halide. Which mechanism made the alkene?Answer: E1. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.2; University of Calgary, Chem 351 course notes, chapter 5. Read 2026-10-03.
A substitution doubles in rate when the nucleophile concentration is doubled, and doubles again when the halide concentration is doubled. Which mechanism is it?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 7.5; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
A substitution runs at the same rate when more nucleophile is added. The rate changes only with the halide concentration. Which mechanism is it?Answer: SN1. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 7.5; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
An alkene forms at a rate given by rate = k[alkyl halide][base]. Which mechanism is it?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.3; University of Calgary, Chem 351 course notes, chapter 5. Read 2026-10-03.
An alkene forms at a rate that depends on the alkyl halide concentration alone; adding more base changes nothing. Which mechanism is it?Answer: E1. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.3; University of Calgary, Chem 351 course notes, chapter 5. Read 2026-10-03.
An elimination has a requirement of shape: the C–H bond that breaks and the bond to the leaving group must lie in one plane, usually anti to each other. Which mechanism is it?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.1; University of Calgary, Chem 351 course notes, chapter 5. Read 2026-10-03.
In one step, a base removes an H from the carbon next to the one bearing the leaving group, the C=C bond forms and the leaving group leaves. Which mechanism is it?Answer: E2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.1; University of Calgary, Chem 351 course notes, chapter 5. Read 2026-10-03.
In one step, a nucleophile bonds to the carbon from the side opposite the leaving group while the leaving group leaves. No intermediate forms. Which mechanism is it?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 7.5; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
The leaving group leaves first and a carbocation forms. A nucleophile then bonds to the carbocation. Which mechanism is it?Answer: SN1. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 7.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
The leaving group leaves first and a carbocation forms. A weak base then removes an H from the next carbon and a C=C bond forms. Which mechanism is it?Answer: E1. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 8.2; University of Calgary, Chem 351 course notes, chapter 5. Read 2026-10-03.
(R)-2-Bromobutane reacts with hydroxide and gives a single enantiomer of 2-butanol, with the configuration at the carbon inverted. Which mechanism made the alcohol?Answer: SN2. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 7.2; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
(S)-3-Bromo-3-methylhexane reacts with water and gives a 50:50 mixture of (R)- and (S)-3-methyl-3-hexanol. Which mechanism made the alcohol?Answer: SN1. Source: Organic Chemistry I, an open text from Kwantlen Polytechnic University (CC BY-NC-SA 4.0), section 7.4; University of Calgary, Chem 351 course notes, chapter 8. Read 2026-10-03.
How this list was compiled: Questions and explanations were written for this site. Every ruling follows two course texts read 2026-10-03, and only cases on which both give the same answer are asked: Organic Chemistry I, an open text from Kwantlen Polytechnic University (X. Liu, CC BY-NC-SA 4.0), chapters 7 and 8, https://kpu.pressbooks.pub/organicchemistry/; and the University of Calgary Chem 351 course notes (I. Hunt), chapters 5 and 8, https://www.chem.ucalgary.ca/courses/351/Carey5th/Carey.html. Facts only, in this site's own words. Licence: own work
How it works
These practice problems for labeling SN1 SN2 E1 E2 reactions give an alkyl halide or tosylate, the nucleophile or base, the solvent and the heat. You name the mechanism, and each answer names the feature that decides it.
Read the full guide
Start with the carbon
A methyl or primary carbon takes SN2 with a good nucleophile; only a bulky strong base turns a primary halide to E2. A tertiary carbon never reacts by SN2.
Then the reagent
A strong base, such as hydroxide or an alkoxide, points to E2 on secondary and tertiary carbons. A good nucleophile that is a weak base, such as iodide, cyanide, azide or a thiolate, points to SN2. Water or an alcohol alone leaves SN1 and E1.
Or read the evidence
A rate that depends on two concentrations means SN2 or E2; on one, SN1 or E1. Inversion marks SN2, and a racemic product marks SN1.
Heat tips a reaction toward elimination.
SN1 and E1 share a carbocation and turn up together, so those problems name the product and ask which one made it.
Questions and answers
What do SN1, SN2, E1 and E2 stand for?
S is substitution, N is nucleophilic and E is elimination. The number counts the species in the rate-determining step: 1 for the substrate alone (unimolecular), 2 for the substrate with the nucleophile or base (bimolecular).
How do you tell SN2 from E2?
Both need a strong reagent. A good nucleophile that is a weak base, such as iodide or a thiolate, substitutes. A strong base, such as hydroxide or an alkoxide, eliminates on secondary and tertiary carbons; a bulky base eliminates on primary ones too.
How do you tell SN1 from E1?
They share a first step: the leaving group departs, which leaves a carbocation. If the nucleophile bonds to the carbocation it is SN1; if a neighboring H is lost and a double bond forms it is E1. Heat favors E1.
Which solvent favors SN1, and which SN2?
Polar protic solvents such as water and alcohols favor SN1, and are often the nucleophile too. Polar aprotic solvents such as acetone, DMSO and DMF favor SN2, because they do not tie up the nucleophile.
Does every problem have one right answer?
Yes. Only cases on which two university course texts agree are asked. A secondary halide in plain water or alcohol, and a primary halide with hydroxide or a small alkoxide, are left out, because no one mechanism clearly leads.