JEE Chemistry Organic Chemistry Some Basic Principles and Techniques MCQs Set 07

Answer: (a) has a more dominating resonance effect than inductive effect

Explanation:
1. Oxygen donates its lone pair to the ring (+M), which outweighs its -I effect, and this activates the ortho and para positions.

Teacher's Note:
1. Key fact to remember: Oxygen donates its lone pair to the ring (+M), which outweighs its -I effect, and this activates the ortho and para positions.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (c) CH\(_3\)CH\(_2^+\) > CH\(_3\)O-CH\(_2^+\)

Explanation:
1. The methoxy group stabilises the adjacent carbocation by lone-pair donation, so CH\(_3\)OCH\(_2^+\) is more stable than the ethyl cation. The other three orders are correct.

Teacher's Note:
1. Key fact to remember: The methoxy group stabilises the adjacent carbocation by lone-pair donation, so CH\(_3\)OCH\(_2^+\) is more stable than the ethyl cation. The other three orders are correct.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (b) delocalisation of pi electrons

Explanation:
1. It is the transmission of electrons through pi bonds or from lone pairs into pi systems, i.e. resonance.

Teacher's Note:
1. Key fact to remember: It is the transmission of electrons through pi bonds or from lone pairs into pi systems, i.e. resonance.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (a) p-nitroaniline

Explanation:
1. The nitro group withdraws electrons by -M and -I effects and reduces the availability of the nitrogen lone pair most.

Teacher's Note:
1. Key fact to remember: The nitro group withdraws electrons by -M and -I effects and reduces the availability of the nitrogen lone pair most.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (c) HCOOH

Explanation:
1. Formic acid is the strongest acid of the four; carboxylates are stabilised by delocalisation over two equivalent oxygens.

Teacher's Note:
1. Key fact to remember: Formic acid is the strongest acid of the four; carboxylates are stabilised by delocalisation over two equivalent oxygens.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (b) naphthalene

Explanation:
1. Naphthalene is planar, cyclic and has 10 pi electrons (4n+2, n = 2). The others have 4 pi electrons and are antiaromatic.

Teacher's Note:
1. Key fact to remember: Naphthalene is planar, cyclic and has 10 pi electrons (4n+2, n = 2). The others have 4 pi electrons and are antiaromatic.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (d) all of them

Explanation:
1. The cyclopropenyl cation has 2 pi electrons, the cyclopentadienyl anion 6, and pyridine 6; each is planar, cyclic and fully conjugated and obeys the 4n+2 rule.

Teacher's Note:
1. Key fact to remember: The cyclopropenyl cation has 2 pi electrons, the cyclopentadienyl anion 6, and pyridine 6; each is planar, cyclic and fully conjugated and obeys the 4n+2 rule.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (c) II > I > III

Explanation:
1. The benzyl carbanion is stabilised by resonance. Alkyl groups destabilise carbanions, so the tertiary anion is the least stable and the methyl anion is between.

Teacher's Note:
1. Key fact to remember: The benzyl carbanion is stabilised by resonance. Alkyl groups destabilise carbanions, so the tertiary anion is the least stable and the methyl anion is between.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (a) electron-donating groups decreasing and electron-withdrawing groups increasing the stability of the phenoxide ion

Explanation:
1. Phenoxide is resonance stabilised, unlike ethoxide, so phenols are more acidic than alcohols. A +I methyl group lowers acidity, while a p-nitro group (-M and -I) raises it.

Teacher's Note:
1. Key fact to remember: Phenoxide is resonance stabilised, unlike ethoxide, so phenols are more acidic than alcohols. A +I methyl group lowers acidity, while a p-nitro group (-M and -I) raises it.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (d) cyclopentene

Explanation:
1. Cyclopentene has an sp\(^3\) carbon, so it is not fully conjugated. The others are planar, cyclic and obey the 4n+2 rule.

Teacher's Note:
1. Key fact to remember: Cyclopentene has an sp\(^3\) carbon, so it is not fully conjugated. The others are planar, cyclic and obey the 4n+2 rule.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (b) D > C > A > B

Explanation:
1. p-Nitrophenol is helped by -M and -I effects; m-nitrophenol is helped by -I only. Methyl is electron-releasing, so p-cresol is the weakest.

Teacher's Note:
1. Key fact to remember: p-Nitrophenol is helped by -M and -I effects; m-nitrophenol is helped by -I only. Methyl is electron-releasing, so p-cresol is the weakest.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (b) o-nitrophenol

Explanation:
1. The nitro group is strongly electron-withdrawing and stabilises the phenoxide ion, and the -I effect is strong at the ortho position.

Teacher's Note:
1. Key fact to remember: The nitro group is strongly electron-withdrawing and stabilises the phenoxide ion, and the -I effect is strong at the ortho position.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (d) m-chlorophenol

Explanation:
1. The -I effect of chlorine stabilises the phenoxide ion, making m-chlorophenol stronger than phenol; the alcohols are much weaker acids.

Teacher's Note:
1. Key fact to remember: The -I effect of chlorine stabilises the phenoxide ion, making m-chlorophenol stronger than phenol; the alcohols are much weaker acids.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (a) benzylamine

Explanation:
1. The lone pair of benzylamine is not delocalised into the ring, so it is the most available and the compound is the strongest base.

Teacher's Note:
1. Key fact to remember: The lone pair of benzylamine is not delocalised into the ring, so it is the most available and the compound is the strongest base.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (c) the resonance effect

Explanation:
1. In vinyl chloride the lone pair of Cl is delocalised towards carbon, which opposes the C-Cl bond dipole and reduces the net dipole moment.

Teacher's Note:
1. Key fact to remember: In vinyl chloride the lone pair of Cl is delocalised towards carbon, which opposes the C-Cl bond dipole and reduces the net dipole moment.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (d) both naphthalene and quinoxaline

Explanation:
1. Both are planar, fully conjugated bicyclic systems with 10 pi electrons, so both follow Huckel's rule.

Teacher's Note:
1. Key fact to remember: Both are planar, fully conjugated bicyclic systems with 10 pi electrons, so both follow Huckel's rule.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (a) ethyne

Explanation:
1. The carbon of ethyne is sp hybridised (50% s-character), so its C-H bond is most acidic and the acetylide ion is the most stable.

Teacher's Note:
1. Key fact to remember: The carbon of ethyne is sp hybridised (50% s-character), so its C-H bond is most acidic and the acetylide ion is the most stable.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (c) m-CH\(_3\)OC\(_6\)H\(_4\)COOH

Explanation:
1. At the meta position the methoxy group acts only by its -I effect, which increases acidity (pK\(_a\) about 4.09). At the para position +M dominates and reduces acidity; acetic acid is weaker than benzoic acid.

Teacher's Note:
1. Key fact to remember: At the meta position the methoxy group acts only by its -I effect, which increases acidity (pK\(_a\) about 4.09). At the para position +M dominates and reduces acidity; acetic acid is weaker than benzoic acid.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (b) vinyl chloride

Explanation:
1. The C-Cl bond has partial double bond character due to resonance, so substitution of Cl is difficult.

Teacher's Note:
1. Key fact to remember: The C-Cl bond has partial double bond character due to resonance, so substitution of Cl is difficult.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (a) \( ^-\)CH\(_2\)-\( ^+\)CH-CH=CH-O-CH\(_3\) (opposite charges on adjacent carbon atoms)

Explanation:
1. The structures with the positive charge on oxygen have complete octets for all atoms, but the structure with a positive carbon next to a negative carbon lacks an octet and has the charges close together, so it contributes least.

Teacher's Note:
1. Key fact to remember: The structures with the positive charge on oxygen have complete octets for all atoms, but the structure with a positive carbon next to a negative carbon lacks an octet and has the charges close together, so it contributes least.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (c) C > D > B > A

Explanation:
1. Para-nitro (-M, -I) increases acidity most, meta-nitro (-I only) less, and the methyl group decreases acidity.

Teacher's Note:
1. Key fact to remember: Para-nitro (-M, -I) increases acidity most, meta-nitro (-I only) less, and the methyl group decreases acidity.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (b) o-nitrophenol

Explanation:
1. The nitro group stabilises the phenoxide ion, making o-nitrophenol more acidic. Ethanol is much less acidic, and methyl and methoxy groups reduce acidity.

Teacher's Note:
1. Key fact to remember: The nitro group stabilises the phenoxide ion, making o-nitrophenol more acidic. Ethanol is much less acidic, and methyl and methoxy groups reduce acidity.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (d) propene

Explanation:
1. Hyperconjugation needs an sp\(^3\) C-H bond next to a pi bond or a carbocation; propene has CH\(_3\) attached to the double bond.

Teacher's Note:
1. Key fact to remember: Hyperconjugation needs an sp\(^3\) C-H bond next to a pi bond or a carbocation; propene has CH\(_3\) attached to the double bond.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (c) CH\(_3\)CH\(_2\)CH\(_2^+\)

Explanation:
1. The primary cation has only two alpha hydrogens for hyperconjugation and no resonance; the others are secondary, tertiary or benzylic.

Teacher's Note:
1. Key fact to remember: The primary cation has only two alpha hydrogens for hyperconjugation and no resonance; the others are secondary, tertiary or benzylic.
2. Revise this point with the matching definition or example in the chapter notes.

Answer: (a) 3-methylbut-1-ene

Explanation:
1. Stability of alkenes increases with the number of hyperconjugating alpha C-H bonds. 3-Methylbut-1-ene has the most alkyl substitution.

Teacher's Note:
1. Key fact to remember: Stability of alkenes increases with the number of hyperconjugating alpha C-H bonds. 3-Methylbut-1-ene has the most alkyl substitution.
2. Revise this point with the matching definition or example in the chapter notes.