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Alcohols, Phenols And Ethers

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Question
CBSEENCH12011136
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Among the following ethers, which one will produce methyl alcohol on treatment with hot concentrated HI?

  • WiredFaculty
  • WiredFaculty
  • WiredFaculty
  • WiredFaculty

Solution

C.

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The ether, which gives more stable carbocation, gives CH3OH as one of the product with hot concentrated HI. the order of stability of carbocation is
30 > 20 > 10
Thus, WiredFaculty  gives CH3 OH as one of the reaction. The reaction proceeds as
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Question
CBSEENCH12011288
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Among the following four compounds

A) Phenol 
B) Methyl Phenol
C) meta - nitrophenol
D) para-nitrophenol

the acidity order is

  • D > C > A > B

  • C > D > A> B

  • A > D > C > B

  • B > A > C> D 

Solution

A.

D > C > A > B

An electron withdrawing group (-I showing group like -NO2, -CN) stabilises the phenoxide ion, thus when present, increases the acidity of phenol. On the other hand, the electron releasing groups (+I showing group like -CH3, -C2H5), when present, decrease the acidity of phenol by destabilising phenoxide ion. Hence, the correct order of acidity of given compound is
p-nitrophenol > m-nitrophenol > phenol > methyl phenol

Question
CBSEENCH12011109
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Among the following sets of reactants which one produces anisole?

  • CH3CHO;RMgX

  • C6H5OH;NaOH; CH3I

  • C6H5OH;neutral FeCl3

  • C6H5-CH3;CH3COCl;AlCl3

Solution

B.

C6H5OH;NaOH; CH3I

Williamson's synthesis
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Question
CBSEENCH11008494
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Consider the following reaction,


Phenol space rightwards arrow with Zn space dust on top space straight X space rightwards arrow from Anhydrous space AlCl subscript 3 to CH subscript 3 Cl of space straight Y space rightwards arrow with Alkaline space KMnO subscript 4 on top straight Z comma
the product,Z,is

  • toluene

  • benzaldehyde

  • benzoic acid

  • benzene

Solution

C.

benzoic acid

i) Zn dust converts - OH group into - H
ii) Reaction with CH3Cl in presence of anhy. AlCl3 is called Friedel -Craft's alkylation.
iii) Alkaline KMnO4 converts complete carbon chain which is directly attached with the benzene ring, into -COOH group.
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Question
CBSEENCH12011264
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Given are cyclohexanol (I), acetic acid (II), 2,4,6-trinitropenol (III) and phenol (IV). In these, the order of decreasing acidic character will be

  • III > II> IV> I

  • II > III> I > IV

  • II > III> IV> I 

  • III > IV> II >  I

Solution

A.

III > II> IV> I

Higher the tendency to give a proton, higher is the acidic character, and tendency to lose a proton depends upon the stability of intermediate, ie, carbanion formed.
2,4,6 - trinitrophenol after the loss of a proton gives 2,4,6 -trinitrophenoxide ion which is stabilised by resonance -I effect and -M effect thus a most acidic among the given compounds. Phenol after losing a proton form phenoxide ion which is also stabilised by resonance, -M and -I effects but is less stabilised as compared to 2,4,6 trinitrophenoxide ions. Thus, it is less acidic as compared to 2,4,6 trinitrophenol. (CH3COOH) after losing a proton give acetate CH3OO- ion which is stabilised by only resonance. However, it is more resonance stabilised as compared to a phenoxide ion, thus more acidic as compared to phenol. 2,4,6 tri-nitrophenol, however, is more acidic than acetic acid due to the presence of three electron withdrawing  - NO2 groups. cyclohexanol gives an anion that is least stable among the given, thus, it is least acidic.
Hence, the correct order of acidic strength is 2,4,6 -trinitrophenol > acetic acid > phenol > cyclohexanol
III> II> IV> I

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