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Alcohols Phenols and Ethers question

2024 · 27 Jan · Shift 1 · Q11
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Alcohols Phenols and Ethers question

2024 · 27 Jan · Shift 1 · Q11

JEE MainChemistryAlcohols Phenols and EthersMCQ+4 / −1
Given below are two statements : Statement (I) : p-nitrophenol is more acidic than m-nitrophenol and o-nitrophenol. Statement (II) : Ethanol will give immediate turbidity with Lucas reagent. In the light of the above statements, choose the correct answer from the options given below :
  1. A
    Statement I is true but Statement II is false
  2. B
    Both Statement I and Statement II are true
  3. C
    Both Statement I and Statement II are false
  4. D
    Statement I is false but Statement II is true
View written solutionFree

Correct answer: A

  1. Evaluate Statement (I): Acidity of nitrophenols

The acidity of nitrophenols depends on the stability of the corresponding phenoxide ion.

  • The −NO2-NO_2−NO2​ group is a strong electron-withdrawing group.
  • At the para and ortho positions, it shows both:
    • −I-I−I effect (inductive withdrawal)
    • −R-R−R effect / resonance withdrawal
  • At the meta position, only the −I-I−I effect operates effectively; resonance interaction with the phenoxide ion is not possible.

So, compared to mmm-nitrophenol, both ooo- and ppp-nitrophenol should be more acidic due to extra resonance stabilization.

However, between ooo-nitrophenol and ppp-nitrophenol:

  • ooo-nitrophenol shows intramolecular hydrogen bonding, which stabilizes the neutral molecule and reduces its tendency to lose H+H^+H+ in water.
  • Hence, ppp-nitrophenol is more acidic than ooo-nitrophenol.

Therefore, the acidity order is: p-nitrophenol>o-nitrophenol>m-nitrophenolp\text{-nitrophenol} > o\text{-nitrophenol} > m\text{-nitrophenol}p-nitrophenol>o-nitrophenol>m-nitrophenol

Thus, the statement p-nitrophenol is more acidic than m-nitrophenol and o-nitrophenolp\text{-nitrophenol is more acidic than } m\text{-nitrophenol and } o\text{-nitrophenol}p-nitrophenol is more acidic than m-nitrophenol and o-nitrophenol is true.

  1. Evaluate Statement (II): Ethanol with Lucas reagent

Lucas reagent is a mixture of: conc. HCl+anhyd. ZnCl2\text{conc. HCl} + \text{anhyd. } ZnCl_2conc. HCl+anhyd. ZnCl2​

It is used to distinguish alcohols:

  • Tertiary alcohols: immediate turbidity
  • Secondary alcohols: turbidity in a few minutes
  • Primary alcohols: no immediate turbidity at room temperature

Ethanol is a primary alcohol. So ethanol does not give immediate turbidity with Lucas reagent.

Hence, Statement (II) is false.

  1. Conclusion
  • Statement (I): True
  • Statement (II): False

Therefore, the correct option is: A\boxed{\text{A}}A​

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