MolSynapse / Question bank / Organic Reaction Mechanisms III: Nucleophilic Substitution / SN1 vs SN2: substrate, nucleophile, solvent, leaving group

SN1 vs SN2: substrate, nucleophile, solvent, leaving group

81 questions on SN1 vs SN2: substrate, nucleophile, solvent, leaving group from the Organic Reaction Mechanisms III: Nucleophilic Substitution chapter: 18 NEET level, 31 JEE Main, 32 JEE Advanced. Each one opens with its answer and solution.

Practice this topic All Organic Reaction Mechanisms III: Nucleophilic Substitution topics

Which carbocation is the most stable? NEET level
Which of the following halides is least able to undergo an SN1 reaction? NEET level
Among the four halides (CH3)3C-X with X = F, Cl, Br, I, the fastest SN1 hydrolysis is shown by NEET level
Which of the following alkyl bromides reacts fastest with water by an SN1 pathway? NEET level
Which of the following is the best leaving group? NEET level
(CH3)3C-OH reacts with concentrated HCl readily by SN1, but does not react with NaCl in water. The role of the acid is to NEET level
In a polar protic solvent, which of the following halides ionises (SN1) most rapidly? JEE Main level
Eight halides are heated separately in 80% aqueous ethanol at 50 degC with no added strong nucleophile: 2-chloro-2-methylpropane, chlorodiphenylmethane, bromobe... JEE Main level
1-Bromobicyclo[2.2.1]heptane (bromine on a bridgehead carbon) is almost inert to solvolysis in aqueous ethanol, although it is a tertiary bromide. The main reas... JEE Main level
Assertion (A): (CH3)3C-OH is converted to (CH3)3C-Cl by concentrated HCl at room temperature, but not by NaCl in neutral water. Reason (R): Protonation converts... JEE Main level
Assertion (A): (CH3)3C-Cl solvolyses much faster than (CH3)2CH-Cl in 80% aqueous ethanol. Reason (R): Nucleophilic approach to the tertiary carbon is less hinde... JEE Main level
Towards iodide ion in acetone (SN2), which order of decreasing reactivity is correct for (a) CH3Br, (b) CH3CH2CH2Br, (c) (CH3)2CHCH2Br, (d) (CH3)3C-CH2Br? JEE Main level
Arrange the leaving groups Cl-, CH3COO-, OH- and NH2- in decreasing order of leaving-group ability. JEE Main level
Under ionising conditions (aqueous formic acid), which of the following benzyl chlorides X-C6H4-CH2-Cl undergoes SN1 solvolysis fastest? JEE Main level
For the tert-butyl derivatives (CH3)3C-X in a polar protic solvent, the correct decreasing order of SN1 reactivity for X is JEE Main level
3-Methylbutan-2-ol is heated with concentrated HBr. The principal bromide formed is JEE Main level
Chloromethyl methyl ether, CH3-O-CH2-Cl, is stirred with excess water. The organic products at the end of the reaction are JEE Advanced level
3,3-Dimethylbutan-2-ol, CH3-CH(OH)-C(CH3)3, is heated with concentrated HBr. The main bromide obtained is JEE Advanced level
Substrates in List I are heated in ethanol (no added base). Match each with the principal substitution product in List II. List I: (P) 1-bromo-1-methylcyclohexa... JEE Advanced level
For first-order ionisation (SN1 pathway) in aqueous ethanol, which order of decreasing rate is correct for (I) (CH3)3C-Br, (II) (CH3)3C-Cl, (III) (CH3)2CH-I, (I... JEE Advanced level
In an ionising solvent, (CH3)3C-Br has a half-life of 20 min for SN1 hydrolysis. Under identical conditions (CH3)3C-Cl reacts 40 times more slowly. If 1.0 M NaO... JEE Advanced level
In each pair, both chlorides give the same set of constitutional alcohols on SN1 hydrolysis in water. Choose the pair(s) for which this is true. JEE Advanced level
Choose the correct statement(s) about the leaving group in SN1 reactions of tertiary substrates. JEE Advanced level
Which of the following halides are practically unreactive towards SN1 solvolysis in aqueous ethanol? JEE Advanced level
Choose the correct relative SN1 solvolysis reactivities (faster > slower) in ionising solvents. JEE Advanced level
The chloromethyl methyl ether CH3-O-CH2-Cl reacts with water. Choose the correct statement(s). JEE Advanced level
In methanol (a polar protic solvent), the correct order of nucleophilicity of the halide ions towards CH3Br is NEET level
Which one of the following is a polar aprotic solvent? NEET level
Bromoethane is warmed with alcoholic KCN. The main organic product is NEET level
Which of the following is the strongest nucleophile towards CH3I in ethanol? NEET level
Among the following neutral species, the best nucleophile towards an alkyl halide in an SN2 reaction is NEET level
The tetrabutylammonium salts of the four halide ions (Bu4N+ X-) are allowed to react with CH3I in dry DMF. The order of the rates of S_N2 substitution is JEE Main level
Sodium azide reacts with 1-bromobutane about 10^3 to 10^5 times faster in DMF than in methanol. The main reason is that JEE Main level
1-Bromopropane is heated with silver nitrite, AgNO2, in ether. The major product and its explanation are JEE Main level
Sodium phenoxide reacts with bromoethane in DMF at 50 degC. The major product is JEE Main level
Towards CH3I in dry DMSO (a solvent in which nucleophilicity follows basicity for the same attacking atom), the correct order of nucleophilic strength of the fo... JEE Main level
The strongest nucleophile towards CH3CH2Br in methanol among the following anions is JEE Main level
Towards CH3I in the corresponding alcohol, ethoxide is a better nucleophile than tert-butoxide even though tert-butoxide is the stronger base. This is because JEE Main level
The reaction CH3CH2Br + N3- -> CH3CH2N3 + Br- is run at a given temperature. Which changes will increase the rate constant of this SN2 reaction? JEE Main level
Assertion (A): The reaction of CH3CH2Br with NaN3 is much faster in DMF than in methanol. Reason (R): DMF is a hydrogen-bond donor and stabilises azide ion stro... JEE Main level
For the reaction of 1-bromobutane with sodium azide (all at the same concentration and temperature), the rate is highest in JEE Main level
Two sequences are carried out on bromoethane. Sequence I: KCN in aqueous ethanol, then boiling with dilute HCl. Sequence II: AgCN in ethanol (covalent, N-bonded... JEE Advanced level
Triethylamine reacts with iodoethane to give tetraethylammonium iodide, an SN2 reaction in which neutral reactants form an ion pair (the Menshutkin reaction). F... JEE Advanced level
Sodium 2-naphthoxide is treated with benzyl bromide in four different solvents. In which solvent is the proportion of ring (C-) alkylation, relative to O-alkyla... JEE Advanced level
Assertion (A): Ethanethiolate, CH3CH2S-, is a better nucleophile than ethoxide, CH3CH2O-, towards CH3I in ethanol, even though ethoxide is the stronger base. Re... JEE Advanced level
Match the reaction in List I (each uses bromoethane as substrate) with the major product in List II, and choose the correct combination. List I: P CH3CH2Br + Na... JEE Advanced level
A small amount of NaI is added to a mixture of 1-chlorobutane in aqueous acetone, in which 1-chlorobutane hydrolyses only slowly. The hydrolysis becomes much fa... JEE Advanced level
The SN2 reaction of RBr with N3- is first order in each reactant. In methanol an initial rate of 3.0 x 10^-9 M s^-1 is measured at [RBr] = 0.020 M and [N3-] = 0... JEE Advanced level
Potassium fluoride is almost insoluble in acetonitrile, and 1-bromooctane is converted into 1-fluorooctane only extremely slowly by it. Addition of a catalytic ... JEE Advanced level
1,4-Dibromobutane (1 mol) is heated with 2 mol of potassium phthalimide in DMF and the product is then boiled with hydrazine hydrate. The final organic product ... JEE Advanced level
Towards CH3I in ethanol, the correct decreasing order of nucleophilic reactivity of the four anions C6H5S-, C2H5O-, Cl-, F- is JEE Advanced level
2-Bromopropane is treated separately with (i) sodium ethanethiolate in ethanol and (ii) potassium tert-butoxide in tert-butanol, each at 50 degC. The major prod... JEE Advanced level
(R)-2-Bromooctane is stirred with NaN3 in DMF (clean SN2), and the product is reduced with LiAlH4, which does not touch the stereocentre. The final product is JEE Advanced level
The alkyl bromides CH3-Br, CH3CH2-Br, (CH3)2CH-Br and (CH3)3C-Br are each treated with NaI in dry acetone at room temperature. Which one reacts fastest by the S... NEET level
CH3CH2CH2-Br is allowed to react with sodium cyanide at the same temperature in four different solvents. In which solvent is the SN2 reaction fastest? NEET level
(CH3)3C-Br undergoes substitution with hydroxide in aqueous acetone by the SN1 mechanism. If the concentration of OH- is tripled while the concentration of the ... NEET level
Which of the following is the best leaving group in a nucleophilic substitution at a saturated carbon? NEET level
(R)-2-Bromobutane, CH3CH2-CH(Br)-CH3, is treated with sodium iodide in dry acetone. The major product is NEET level
(R)-Butan-2-ol is treated with thionyl chloride in the presence of pyridine. The main product is NEET level
(S)-Butan-2-ol is converted into 2-bromobutane by phosphorus tribromide. Which statement describes the product correctly? NEET level
Rank the following in decreasing order of rate of solvolysis (SN1) in aqueous ethanol at 25 degC: I (CH3)3C-Br, II (CH3)2CH-Br, III CH3CH2-Br, IV (C6H5)3C-Br. JEE Main level
Rank the following in decreasing order of SN2 reactivity towards NaI in dry acetone: I CH3CH2-Br, II (CH3)2CHCH2-Br, III (CH3)3CCH2-Br, IV CH3CH2CH2-Br. JEE Main level
Optically pure (R)-3-bromo-3-methylhexane is left in neutral methanol (solvolysis). Assume that the reaction goes entirely through a free planar carbocation and... JEE Main level
(S)-CH3-CH(OTs)-CH2-OCH3 (OTs = tosylate) reacts with sodium cyanide in DMSO by a clean SN2 pathway. The product CH3-CH(CN)-CH2-OCH3, 3-methoxy-2-methylpropanen... JEE Main level
(S)-1-Phenylethanol, C6H5-CH(OH)-CH3, is converted into 1-chloro-1-phenylethane by (i) SOCl2 in pyridine and (ii) SOCl2 alone (no base, non-nucleophilic solvent... JEE Main level
Which sequence converts (R)-butan-2-ol into (S)-butan-2-ol, with a single net inversion at the stereocentre? (Assume every substitution step is a clean SN2 reac... JEE Main level
Match the reaction in List I with the stereochemical outcome in List II. List I: P (S)-2-bromooctane + NaN3 in DMF; Q (R)-3-bromo-3-methylhexane in aqueous acet... JEE Main level
Assertion (A): The SN2 reaction of CH3CH2CH2-Br with NaCN is faster in DMSO than in methanol. Reason (R): DMSO has a higher boiling point than methanol. JEE Main level
A student wants to identify the tertiary alcohol among four unlabelled samples using ZnCl2 in concentrated HCl (Lucas reagent) at room temperature, where turbid... JEE Main level
An SN2 reaction of an alkyl halide RX with an anionic nucleophile in methanol has rate = k[RX][Nu-] and an initial rate of 3.0x10^-5 mol L^-1 s^-1 when [RX] = 0... JEE Main level
Select the correct statement(s) about the SN2 reaction of an alkyl halide with an anionic nucleophile. JEE Main level
(R)-3-Methylbutan-2-ol, (CH3)2CH-CH(OH)-CH3, is heated with concentrated aqueous HBr. The major substitution product is JEE Advanced level
2,2-Dimethylpropyl (neopentyl) tosylate, (CH3)3C-CH2-OTs, is heated in absolute ethanol with no added base. Ignoring elimination products, the major substitutio... JEE Advanced level
(R)-Octan-2-ol is treated successively with (i) TsCl in pyridine, (ii) NaN3 in DMF (clean SN2), and (iii) H2 over Pd/C, which reduces the azide to the amine wit... JEE Advanced level
In which of the following reactions does the stereocentre undergo net inversion of its spatial configuration (not merely a change of the letter)? JEE Advanced level
Select the correct statement(s) about the conversion of alcohols into alkyl halides. JEE Advanced level
For the solvolysis of benzylic chlorides Ar-CH2Cl in 80 % aqueous ethanol and their reaction with NaI in dry acetone, select the correct statement(s). JEE Advanced level
3-Chlorobut-1-ene, CH2=CH-CH(Cl)-CH3, is heated in neutral water, where it ionises (SN1) to an allylic carbocation that is captured by water. Ignoring eliminati... JEE Advanced level
1-Bromobicyclo[2.2.1]heptane (bromine at a bridgehead) is almost inert both to NaI in acetone and to boiling aqueous ethanol, whereas (CH3)3C-Br reacts readily ... JEE Advanced level
(S)-2-Phenyloxirane (styrene oxide) is opened in two ways: (i) with methanol containing a catalytic amount of H2SO4, where methanol attacks the carbon that best... JEE Advanced level
The ring in 4-tert-butylcyclohexyl tosylate is locked in the chair in which the tert-butyl group is equatorial. The cis and trans isomers are each treated with ... JEE Advanced level