GOC & Aromaticity - 2 - GATE Chemistry MCQ

As we know that acidic b ehaviour 
Then the least acidic com pound will have highest pK_a.  Here, conjugate base of Q will be most stable and thus, will be most acidic and thus Q will be most stable and thus, will be most acidic and thus Q have lowest pK_{a .} On the other hand T will be more acidic as compared to S. because S involves cross conjugation. U will be least acidic. Thus, order of pK_a value will be 
Q < T < S < P < R < U

Conjugate base of I, II. Ill, IV and V are


Here. II will be the most stable because of extensive delocalization and equal contributing resonance structure, followed by V in which negative charge is delocalized over additional phenyl ring.
Thus, acidity order will be
II > V > IV > III > I

Electron donating group decreases acidic behaviour.
• For hyper conjugation and resonance to happen, the overlapping atom must be planer
• The moment, there is deviation from planarity, because of any reason (here because of steric repulsion) the said effect will minimize or will be diminished.
Becuase of steric effect least donation will be in I, thus will be most acidic Hence, acidic order will be I > II > III.

Rate of electrophilic aromatic substitution reaction depends upon availability of electron cloud
• Effect of an atom as an electron withdrawing group will be more, when it will be present in the ring, as compared to when it will present outside the ring. Thus, the rate of EAS will be I > III > II. Hence, option (d) is correct.

Rate of S_N1 reaction ∝ stability of carbocation

Thus, stability order will be III > I > II
Hence, rate of S_N1 will also be in same order III > I > II

it exist predominately in the enol form, in which O-H bond is considerably polar, hence have high dipole moment.
Since, it predominately exist in enol form. It gives reaction corresponding to phenol and not corresponding to ketone. That is why it given FeClj test as well as Reimer Tiemann reaction, but does not gives DNP test.

Reactivity towards nucleophile means electrophilicity. Electrophilic character at Carbonyl carbon depends upon the neighbouring group. Electron releasing group decrease electrophilicity and electron withdrawing group increase electrophilicity. Negative charge containing atom are better donar as compared to lone pair containing atom. Less electronegative atom (N) is better donar as compared to more electronegative atom (O). So electrophilic order

More stabilized conjugate base with more acidity

Resonance involve movement of charge in bond whereas tautomerism involved movemerts of atom takes place.

 having lower activation energy so they act as more nucleophile.

Lone pair- containing atom with conjugation show (+M) effect.
A, B, E, F ( + M ) effect
C, D, G, H ( - M ) effect

A → Aromatic
B → Aromatic
C → Non-aromatic
D → Aromatic
E → Aromatic
D → Aromatic