Question 1

In Finkelstein reaction, which one of the following reagents is used?

Accepted Answer

The Finkelstein reaction is a halogen exchange reaction used for the synthesis of alkyl iodides from alkyl chlorides or alkyl bromides. The reaction involves treating an alkyl chloride or bromide with sodium iodide (NaI) in dry acetone. R-X + NaI dry acetone R-I + NaX where X = Cl, Br. Sodium iodide is soluble in dry acetone, whereas sodium chloride and sodium bromide are insoluble and precipitate out. This precipitation drives the forward reaction according to Le Chatelier's principle. Answer:

Question 2

What is the major product formed when 2-bromopentane reacts with alcoholic KOH?

Accepted Answer

Reaction of 2-bromopentane with alcoholic KOH undergoes dehydrohalogenation (E2 elimination). CH_3-CH(Br)-CH_2-CH_2-CH_3 alc. KOH, CH_3-CH=CH-CH_2-CH_3 + CH_2=CH-CH_2-CH_2-CH_3 According to Zaitsev's rule, the more substituted alkene is formed as the major product. Pent-2-ene is a disubstituted alkene, whereas pent-1-ene is a monosubstituted alkene. Thus, pent-2-ene is the major product. Answer: Pent-2-ene

Question 3

Which reagent is used to convert Alkyl halide into Alkyl nitrite ?

Accepted Answer

Potassium nitrite (KNO_2) is an ionic compound and provides nitrite ions (NO_2^-) in the solution. The nitrite ion is an ambidentate nucleophile with two donor sites: oxygen and nitrogen. Since the K-O bond is ionic, the negative charge on the oxygen atom is available for nucleophilic attack on the alkyl halide. This results in the formation of an alkyl nitrite (R-O-N=O) as the major product. In contrast, silver nitrite (AgNO_2) has a covalent Ag-O bond, making the lone pair on the nitrogen atom

Question 4

Which among the following is NOT a feature of SN ^2 mechanism ?

Accepted Answer

The S_N2 mechanism is a single-step concerted reaction where bond breaking and bond forming occur simultaneously. It involves the backside attack of the nucleophile on the substrate, leading to the inversion of configuration. The reaction proceeds via a transition state and does not involve the formation of any intermediate. The formation of a planar carbocation intermediate is a characteristic feature of the S_N1 mechanism, not the S_N2 mechanism. Answer: Formation of planar carbocation interme

Question 5

Identify the product 'B' in the following reaction sequence.

Accepted Answer

The given reaction sequence involves the formation of a Grignard reagent followed by its reaction with an alcohol. Step 1: The reactant 2-chlorobutane reacts with magnesium (Mg) in the presence of dry ether to form a Grignard reagent, sec-butylmagnesium chloride (A). CH_3-CH_2-CH(Cl)-CH_3 Mg, Dry ether CH_3-CH_2-CH(MgCl)-CH_3 Step 2: Grignard reagents are strong bases and react vigorously with compounds containing acidic hydrogen atoms, such as alcohols, water, and amines, to form alkanes. Ethan

Question 6

Identify the product B in following reaction. CH _3 Br KCN A [ C _2 H _5 OH ] Na B

Accepted Answer

The reaction of methyl bromide ( CH _3 Br ) with potassium cyanide ( KCN ) is a nucleophilic substitution reaction which yields ethanenitrile ( CH _3 CN ) as the major product A. CH _3 Br + KCN CH _3 CN + KBr The reduction of ethanenitrile ( CH _3 CN ) with sodium and ethanol ( Na / C _2 H _5 OH ) is known as the Mendius reduction. It reduces the nitrile group to a primary amine, yielding ethanamine ( CH _3 CH _2 NH _2) as product B. CH _3 CN + 4[ H ] Na / C _2 H _5 OH CH _3 CH _2 NH _2 Answer:

Question 7

Which from the following compounds is not obtained when methyl bromide is treated with ethyl bromide in presence of sodium metal in dry ether?

Accepted Answer

The reaction of methyl bromide and ethyl bromide with sodium metal in dry ether is an example of the Wurtz reaction. The alkyl free radicals formed during the reaction are methyl radical (CH_3^ ) and ethyl radical (C_2H_5^ ). These radicals can undergo self-coupling as well as cross-coupling to give a mixture of alkanes: CH_3^ + CH_3^ CH_3-CH_3 (Ethane) C_2H_5^ + C_2H_5^ CH_3-CH_2-CH_2-CH_3 (n-Butane) CH_3^ + C_2H_5^ CH_3-CH_2-CH_3 (Propane) 2-methyl propane cannot be formed by the coupling of m

Question 8

Which of the following n mole compound is obtained when 2n moles of C _6 H _5 Cl treated of with 2n mole sodium atom in dry ether?

Accepted Answer

The reaction of an aryl halide with sodium in the presence of dry ether to form a diaryl compound is known as the Fittig reaction. The chemical equation for the reaction is: 2 C _6 H _5 Cl + 2 Na dry ether C _6 H _5- C _6 H _5 + 2 NaCl From the stoichiometry of the reaction, 2 moles of chlorobenzene react with 2 moles of sodium to produce 1 mole of biphenyl. Therefore, 2n moles of chlorobenzene reacting with 2n moles of sodium will produce n moles of biphenyl. Answer: Biphenyl

Question 9

Identify reagent B in following reaction. R - X \ B \ Nitroalkane

Accepted Answer

The reaction of an alkyl halide with silver nitrite ( AgNO _2) yields a nitroalkane as the major product. AgNO _2 is predominantly covalent in nature. The bond between silver and oxygen ( Ag - O ) is covalent, which leaves the lone pair of electrons on the nitrogen atom available for nucleophilic attack. Therefore, the nucleophilic attack on the alkyl halide occurs through the nitrogen atom, resulting in the formation of a nitroalkane ( R - NO _2). In contrast, potassium nitrite ( KNO _2) is an

Question 10

Identify substrate 'S' in the following reaction. S Na / dry ether 3, 4 - diethyl - 3, 4 - dimethyl hexane

Accepted Answer

The given reaction is a Wurtz reaction, which involves the coupling of two alkyl halide molecules in the presence of sodium and dry ether to form a symmetrical alkane. The structure of the product, 3,4-diethyl-3,4-dimethylhexane, is: CH _3 -CH _2 -C(CH _3 )(CH _2 CH _3 )-C(CH _3 )(CH _2 CH _3 )-CH _2 -CH _3 Since the Wurtz reaction produces a symmetrical alkane by the dimerization of alkyl radicals, we can determine the structure of the reactant by cleaving the central carbon-carbon bond of the

Question 11

The reaction of aryl halide with sodium metal in dry ether to give biphenyl is known as

Accepted Answer

The reaction of an aryl halide with sodium metal in the presence of dry ether to form biphenyl is known as the Fittig reaction. 2 Ar-X + 2 Na dry ether Ar-Ar + 2 NaX The Wurtz reaction involves two alkyl halides to form an alkane, while the Wurtz-Fittig reaction involves one alkyl halide and one aryl halide to form an alkylarene. The Swarts reaction is used for the synthesis of alkyl fluorides. Answer: Fittig reaction

Question 12

Identify the product obtained when 2- Chloro - 2 - methylbutane is reacted with sodium metal in presence of dry ether?

Accepted Answer

The given reactant is 2-chloro-2-methylbutane, which has the structure CH_3-C(Cl)(CH_3)-CH_2-CH_3. When reacted with sodium metal in the presence of dry ether, it undergoes the Wurtz reaction. The reaction proceeds via the formation of an alkyl free radical. The cleavage of the C-Cl bond yields the radical CH_3-C^ (CH_3)-CH_2-CH_3. Two such radicals dimerize to form the final alkane product: 2 CH_3-C(Cl)(CH_3)-CH_2-CH_3 + 2 Na CH_3-CH_2-C(CH_3)_2-C(CH_3)_2-CH_2-CH_3 + 2 NaCl The longest continuo

Question 13

Identify the product obtained when 2-chlorobutane is heated with aqueous solution of potassium hydroxide.

Accepted Answer

When an alkyl halide is treated with an aqueous solution of potassium hydroxide (KOH), it undergoes a nucleophilic substitution reaction. The hydroxide ion (OH^-) acts as a nucleophile and replaces the halogen atom. For 2-chlorobutane, the reaction proceeds as follows: CH_3-CH(Cl)-CH_2-CH_3 + KOH(aq) CH_3-CH(OH)-CH_2-CH_3 + KCl The chlorine atom at the second carbon is substituted by a hydroxyl group, resulting in the formation of Butan-2-ol. Answer: Butan - 2 - ol

Question 14

Which among the following is allylic halide?

Accepted Answer

An allylic halide is a compound in which the halogen atom is bonded to an sp^3 hybridized carbon atom that is adjacent to a carbon-carbon double bond (C=C). In CH _3 - CH _2 - CH _2 - X , the halogen is attached to an sp^3 carbon of an alkane chain, making it an alkyl halide. In C _6 H _5 - CH _2 - X , the halogen is attached to an sp^3 carbon adjacent to a benzene ring, making it a benzylic halide. In CH _2 = CH - CH _2 - X , the halogen is attached to an sp^3 hybridized carbon atom which is di

Question 15

Which of the following reactions is used for the preparation of alkyl fluorides from alkyl chlorides?

Accepted Answer

Swarts reaction is the standard method used for the preparation of alkyl fluorides from alkyl chlorides or bromides. In this reaction, heating an alkyl chloride or bromide in the presence of a metallic fluoride such as AgF, Hg_2F_2, CoF_3, or SbF_3 yields the corresponding alkyl fluoride. R-Cl + AgF R-F + AgCl Finkelstein reaction is used for the preparation of alkyl iodides. Sandmeyer's reaction is used for the preparation of aryl halides from diazonium salts. Fittig reaction is used for the pr

Question 16

What is the product P obtained in following reaction? CH _3 CH _2 Br + AgCN _ (alc) P

Accepted Answer

AgCN is predominantly a covalent compound. The bond between Ag and C is covalent, which leaves the lone pair of electrons on the nitrogen atom available for nucleophilic attack. When an alkyl halide such as CH _3 CH _2 Br reacts with alcoholic AgCN , the nucleophilic attack occurs through the nitrogen atom rather than the carbon atom. This results in the formation of an alkyl isocyanide as the major product. CH _3 CH _2 Br + AgCN _ (alc) CH _3 CH _2 NC + AgBr The product P is ethyl isocyanide, C

Question 17

Identify the reagent used for replacement of - N _2^+ Cl ^- from benzene diazonium chloride by iodine.

Accepted Answer

Benzene diazonium chloride reacts with aqueous potassium iodide (KI) upon warming to form iodobenzene. The reaction is given by: C _6 H _5 N _2^+ Cl ^- + KI C _6 H _5 I + N _2 + KCl Therefore, the reagent used for the replacement of the diazonium group by iodine is KI. Answer: KI

Question 18

Which of the following alkyl halides undergoes SN ^1 reaction most readily?

Accepted Answer

The rate of an SN ^1 reaction depends on the stability of the carbocation formed and the leaving group ability of the halide ion. Since the alkyl group is the same in all the given options, the carbocation formed is the tert-butyl carbocation, ( CH _3)_3 C ^+, in each case. The rate of reaction will therefore depend on the leaving group ability of the halide ion. A better leaving group leads to a faster reaction. The leaving group ability increases as the size of the halogen atom increases and t

Question 19

Which of the following alkyl halides is hydrolyzed most rapidly by the SN ^2 mechanism ?

Accepted Answer

The rate of an SN ^2 reaction is inversely proportional to the steric hindrance around the carbon atom bearing the leaving group. The order of reactivity of alkyl halides towards SN ^2 mechanism is: Methyl halide > 1^ alkyl halide > 2^ alkyl halide > 3^ alkyl halide. Among the given options: CH _3 -Br is a methyl halide. CH _3 -CH _2 -Br is a 1^ alkyl halide. ( CH _3)_2 CH-Br is a 2^ alkyl halide. ( CH _3)_3 C-Br is a 3^ alkyl halide. Since CH _3 -Br has the least steric hindrance, it is hydroly

Question 20

Method of preparation of alkyl halide 2 R-Br + Hg _2 F _2 2 R-F + Hg _2 Br _2 This reaction is known as

Accepted Answer

The synthesis of alkyl fluorides is best accomplished by heating an alkyl chloride or bromide in the presence of a metallic fluoride such as AgF , Hg _2 F _2, CoF _2, or SbF _3. The given reaction involves the conversion of an alkyl bromide to an alkyl fluoride using mercurous fluoride ( Hg _2 F _2). 2 R-Br + Hg _2 F _2 2 R-F + Hg _2 Br _2 This halogen exchange reaction for the preparation of alkyl fluorides is known as the Swarts reaction.

Haloalkanes and Haloarenes — Previous Year Questions & Solutions