Mesomeric effect and steric inhibition of resonance

27 questions on Mesomeric effect and steric inhibition of resonance from the General Organic Chemistry I: Electronic Effects chapter: 5 NEET level, 11 JEE Main, 11 JEE Advanced. Each one opens with its answer and solution.

• Which of the following groups shows a +M (positive mesomeric) effect when attached to a benzene ring? NEET level
• Which of the following groups shows a -M (negative mesomeric) effect? NEET level
• In nitrobenzene, the -NO2 group affects the electron density of the ring as follows: NEET level
• The halogen atom in chlorobenzene shows NEET level
• Which statement about the mesomeric effect is correct? NEET level
• Arrange in decreasing order of electron density in the benzene ring: (I) C6H5-NH2, (II) C6H5-OCH3, (III) C6H5-Cl, (IV) C6H5-NO2. JEE Main level
• Arrange in decreasing order of acidity: (I) 4-nitrophenol, (II) 3-nitrophenol, (III) phenol. JEE Main level
• Arrange in decreasing order of acid strength: (I) 4-nitrobenzoic acid, (II) benzoic acid, (III) 4-methoxybenzoic acid. JEE Main level
• Arrange in decreasing order of acidity: (I) 4-nitrophenol, (II) 3,5-dimethyl-4-nitrophenol, (III) phenol. JEE Main level
• Arrange in decreasing order of acid strength: (I) 2,6-dimethylbenzoic acid, (II) benzoic acid, (III) 4-methylbenzoic acid. JEE Main level
• Arrange in decreasing order of basicity in water: (I) 4-methylaniline, (II) aniline, (III) 4-nitroaniline. JEE Main level
• In CH2=CH-CHO, which atom carries the greater partial positive charge among the two alkene carbons, and why? JEE Main level
• The C-Cl bond length in chloroethene (CH2=CH-Cl), compared with that in chloroethane, is JEE Main level
• Which of the following groups, when attached to a benzene ring, show a -M (negative mesomeric) effect? JEE Main level
• In which of the following compounds is resonance of a substituent with the ring significantly diminished by steric inhibition of resonance? JEE Main level
• Which of the following statements are correct? JEE Main level
• The pKa values of phenol and 4-nitrophenol in water at 298 K are 9.99 and 7.15 respectively. By what factor is K_a of 4-nitrophenol greater than K_a of phenol? JEE Advanced level
• Which of the following compounds has the larger dipole moment, and why? (P) 4-nitro-N,N-dimethylaniline, (Q) 3,5-dimethyl-4-nitro-N,N-dimethylaniline. JEE Advanced level
• Arrange in decreasing order of acid strength: (I) 2,6-dimethylbenzoic acid, (II) 2-methylbenzoic acid, (III) benzoic acid, (IV) 4-methylbenzoic acid. JEE Advanced level
• Assertion (A): 4-Nitrophenol is more acidic than 3-nitrophenol. Reason (R): In 4-nitrophenoxide the negative charge on oxygen can be delocalised onto the nitro ... JEE Advanced level
• Arrange in decreasing order of the C-N bond length: (I) CH3-NH2, (II) C6H5-NH2, (III) 4-nitroaniline (C-N bond to the ring). JEE Advanced level
• Arrange the following in decreasing order of reactivity towards nucleophilic acyl substitution: (I) ethanoyl chloride, (II) ethanoic anhydride, (III) ethyl etha... JEE Advanced level
• Arrange in decreasing order of reactivity towards nucleophilic addition of HCN: (I) 4-nitrobenzaldehyde, (II) benzaldehyde, (III) 4-methoxybenzaldehyde. JEE Advanced level
• Arrange in decreasing order of basicity: (I) 4-aminopyridine, (II) 3-aminopyridine, (III) pyridine, (IV) 4-nitropyridine. JEE Advanced level
• In which of the following do the groups exhibit a +M effect when attached to a benzene ring? JEE Advanced level
• Which of the following phenols are stronger acids than phenol? JEE Advanced level
• Which of the following statements about amines are correct? JEE Advanced level