MCQs Of Alcohols, Phenols And Ethers, Past Year Questions - JEE Mains, Class 12, Chemistry


20 Questions MCQ Test Class 12 Chemistry 35 Years JEE Mains &Advance Past yr Paper | MCQs Of Alcohols, Phenols And Ethers, Past Year Questions - JEE Mains, Class 12, Chemistry


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QUESTION: 1

During dehydration of alcohols to alkenes by heating withconc. H2SO4 the initiation step is [2003]

Solution:

The dehydration of alcohol to form alkene occurs in following three step. Step (1) is initiation step.
Step (1) Formation of protonated alcohol.

Step (2) Formation of carbocation

Step (3)Elimination of a proton to form ethene

QUESTION: 2

Among the following compounds which can be dehydrated very easily is                 [2004]

Solution:

3-methyl pentanol-3 will be dehydrated most readily since it produces tertiary carbonium ion as intermediate.

QUESTION: 3

The best reagent to convert pent-3-en-2-ol into pent-3-in-2-one is     [2005]

Solution:


Pyridiminum chloro-chromate (PCC) is specific for the conversion.

QUESTION: 4

p -cresol reacts with chloroform in alkaline medium to give the compound A which adds hydrogen cyanide to form, the
compound B. The latter on acidic hydrolysis gives chiral carboxylic acid. The structure of the carboxylic acid is
[2005]

Solution:

 

QUESTION: 5

HBr reacts with CH2 = CH – OCH3 under anhydrous conditions at room temperature to give         [ 2006]

Solution:

Methyl vinyl ether under anhydrous condition at room temperature undergoes addition reaction.

QUESTION: 6

Among the following the one that gives positive iodoform test upon reaction with I2 and NaOH is [ 2006]

Solution:

Only those alcohols which contain –CHOHCH3 group undergo haloform reaction. Among the given options only (b) contain this group, hence undergo haloform
reaction.

QUESTION: 7

The structure of the compound that gives a tribromo derivative on treatment with bromine water is [2006]

Solution:

NOTE : OH group activates the benzene nucleus and

QUESTION: 8

The electrophile involved in the above reaction is

Solution:

NOTE : This is Riemer-Tiemann reaction and the electrophile is dichlorocarbene.

QUESTION: 9

In the following sequence of reactions, 

the compound D is              [2007

Solution:

QUESTION: 10

Phenol, when it first reacts with concentrated sulphuric acidand then with concentrated nitric acid, gives             [2008]

Solution:

Phenol on reaction with conc. H2SO4 gives a mixture of o- and p- products (i.e., –SO3H group, occupies o-, p- position). At room temperature o-product is more stable, which on treatment with conc. HNO3 will yield
o-nitrophenol.

At room temperature o- product is more stable

Hence (b) is the correct answer.

QUESTION: 11

The major product obtained on interaction of phenol withsodium hydroxide and carbon dioxide is       [2009]

Solution:

QUESTION: 12

From amongst the following alcohols the one that wouldreact fastest with conc. HCl and anhydrous ZnCl2, is [2010]

Solution:

Tertiary alcohols react fastest with conc. HCl and anhydrous ZnCl2 (lucas reagent) as its mechanism proceeds through the formation of stable tertiary carbocation.
Mechanism

QUESTION: 13

The main product of the following reaction is 

Solution:

Whenever dehydration can produce two different alkenes, major product is formed according to Saytzeff rule i.e. more substituted alkene (alkene having lesser
number of hydrogen atoms on the two doubly bonded carbon atoms) is the major product.
Such reactions which can produce two or more structural isomers but one of them in greater amounts than the other are called regioselective ; in case a reaction is 100% regioselective, it is termed as regiospecific.
In addition to being regioselective, alcohol
dehydrations are stereoselective (a reaction in which a single starting material can yield two or more stereoisomeric products, but gives one of them in greater amount than any other).

 

QUESTION: 14

Phenol is heated with a solution of mixture of KBr and KBrO3. The major product obtained in the above reaction is :[2011]

Solution:

QUESTION: 15

Arrange the following compounds in order of decreasing acidity :

Solution:

Electron withdrawing substituents like –NO2, Cl increase the acidity of phenol while electron releasing substituents like – CH3, – OCH3 decreases acidity. hence the correct order of acidity will be

Further (– I) NO2 > (–I) Cl and (+ I) CH3 > (+I) OCH3

QUESTION: 16

An unknown alcohol is treated with the “Lucas reagent” todetermine whether the alcohol is primary, secondary ortertiary. Which alcohol reacts fastest and by what mechanism:[JEE M 2013]

Solution:

Tertiary alchols reacts fastest with lucas reagnet as the rate of reaction is directly proportional to the stability of carbocation formed in the reaction. Since most stable
3° carbocation is formed in the reaction hence it will react fastest further tetriary alcohols appears to react by SN1 mechanism.

 

QUESTION: 17

Sodium phenoxide when heated with CO2 under pressure at 125ºC yields a product which on acetylation produces C.

The major product C would be                           [JEE M 2014]

Solution:

 

 

QUESTION: 18

Thiol group is present in :                     [JEE M 2016]

Solution:

Among 20 naturally occuring amino acids "Cysteine" has '– SH' or thiol functional group.
⇒ General formula of amino acid 

⇒ Value of R = –CH2–SH in Cysteine.

QUESTION: 19

The product of the reaction given below is:                 [JEE M 2016]

Solution:

N – bromosuccinimide results into bromination at allylic and benzylic positions

QUESTION: 20

2-chloro-2-methylpentane on reaction with sodium methoxide in methanol yields: [JEE M 2016]
 

(i) 

 

(ii)

 

(iii)

Solution:

When tert -alkyl halides are used in Williamson synthesis elimination occurs rather than substitution resulting into formation of alkene. Here alkoxide ion abstract one of the b-hydrogen atom along with acting
as a nucleophile.