For the given compounds, the correct order of increasing \(pK_a\) value :
\((E)<(D)<(C)<(B)<(A)\)
\((D)<(E)<(C)<(B)<(A)\)
\((E)<(D)<(B)<(A)<(C)\)
\((B)<(D)<(A)<(C)<(E)\)
- None of these
The Correct Option is
Approach Solution - 1
To determine the order of increasing \(pK_a\) values for the given compounds, we need to evaluate their acidic strength. The \(pK_a\) value is inversely related to acidity; the lower the \(pK_a\), the stronger the acid.
Let's analyze the compounds one by one considering their substituents:
- Compound (A): Phenol. The hydroxyl group is attached to the benzene ring without any electron-withdrawing or electron-donating groups.
- Compound (B): 2-nitrophenol. The nitro group is a strong electron-withdrawing group, making the compound more acidic than phenol.
- Compound (C): 2-hydroxyanisole. The methoxy group is an electron-donating group, reducing acidity compared to phenol.
- Compound (D): 4-nitrophenol. The nitro group increases the acidity significantly compared to phenol due to electron-withdrawing effects.
- Compound (E): 2-methoxyphenol. The methoxy group donates electrons, reducing acidity compared to phenol.
Based on the substituents, the relative acidic strength is:
- Most acidic: 4-nitrophenol (D) - Strong electron-withdrawing group at para position.
- 2-nitrophenol (B) - Strong electron-withdrawing group at ortho position.
- Phenol (A) - Baseline acidity.
- 2-methoxyphenol (E) - Electron-donating group reducing acidity.
- Least acidic: 2-hydroxyanisole (C) - Electron-donating group reducing acidity further.
Thus, the correct order of increasing \(pK_a\) values is:
\((C) < (E) < (A) < (B) < (D)\)
The provided options do not match this order, confirming the correct answer is "None of these."
Approach Solution -2
Explanation:
- Definition of \( pK_a \): Lower \( pK_a \) corresponds to a stronger acid.
- Factors affecting \( pK_a \):
- Electron-withdrawing groups (EWG) increase acidity by stabilizing the conjugate base.
- Electron-donating groups (EDG) decrease acidity by destabilizing the conjugate base.
- Order Analysis:
- (D) Dinitrophenol: Strongest acid due to two nitro (EWG) groups stabilizing the phenoxide ion.
- (B) Nitrophenol: Less acidic than (D), but still acidic due to one nitro group.
- (A) Phenol: Less acidic than (B) due to the absence of strong EWGs.
- (C) Methoxyphenol: The methoxy group (EDG) destabilizes the phenoxide ion, making it less acidic than phenol.
- (E) Methoxy-dinitrophenol: The methoxy group reduces the effect of the nitro groups, making it less acidic than dinitrophenol but more acidic than phenol.
- Final Order: \[ (D) < (B) < (A) < (C) < (E). \]
Final Answer: None of these.
Top JEE Main Chemistry Questions
What will be the equilibrium constant of the given reaction carried out in a \(5 \,L\) vessel and having equilibrium amounts of \(A_2\) and \(A\) as \(0.5\) mole and \(2 \times 10^{-6}\) mole respectively?
The reaction : \(A_2 \rightleftharpoons 2A\)- At equilibrium the concentrations of and in a sealed vessel at . What will be for the reaction
- Find out the major products from the following reactions
Cobalt chloride when dissolved in water forms pink colored complex $X$ which has octahedral geometry. This solution on treating with cone $HCl$ forms deep blue complex, $\underline{Y}$ which has a $\underline{Z}$ geometry $X, Y$ and $Z$, respectively, are
- The correct order of atomic radii is:
Top JEE Main Organic Chemistry Questions
- Example of vinylic halide is
- Structure of 4-Methylpent-2-enal is
- In the given reactions identify the reagent A and reagent B
- Given below are two statement one is labeled as Assertion (A) and the other is labeled as Reason (R).
Assertion (A): CH2 = CH – CH2 – Cl is an example of allyl halide
Reason (R): Allyl halides are the compounds in which the halogen atom is attached to sp2 hybridised carbon atom.
In the light of the two above statements, choose the most appropriate answer from the options given below - Following is a confirmatory test for aromatic primary amines. Identify reagent (A) and (B)
Top JEE Main Questions
- In a hydrogen like atom, when an electron jumps from the $M$ - shell to the $L$ - shell, the wavelength of emitted radiation is $\lambda$. If an electron jumps from $N$-shell to the $L$-shell, the wavelength of emitted radiation will be :
- Two masses $m$ and $\frac{m}{2}$ are connected at the two ends of a massless rigid rod of length $l$. The rod is suspended by a thin wire of torsional constant $k$ at the centre of mass of the rod-mass system(see figure). Because of torsional constant $k$, the restoring torque is $\tau =k\theta$ for angular displacement $\theta$. If the rod is rota ted by $\theta_0$ and released, the tension in it when it passes through its mean position will be:
What will be the equilibrium constant of the given reaction carried out in a \(5 \,L\) vessel and having equilibrium amounts of \(A_2\) and \(A\) as \(0.5\) mole and \(2 \times 10^{-6}\) mole respectively?
The reaction : \(A_2 \rightleftharpoons 2A\)- The value of is
- The number of terms of an is even. The sum of the odd terms is and of the even terms is . The last term exceeds the first by . Then the number of terms in the series is ______.