Hydroxy Compounds

Question 1

Alcohols and Phenols

Answer 1

• -OH bonded to a saturated C(sp³ hybridised) of an alkyl group
• -OH bondeddirectly to a C(sp² hybridised) in the benzene ring

Question 2

Why does 2-nitrophenol has a lower boiling point than 4-nitrophenol

Answer 2

• intramolecular hydrogen bonding due to close proximity of the -OH group and -NO₂
• reduces number of sites available for intermolecular hydrogen bonding
• less. Energy is required to overcome the less extensive intermolecular hydrogen bonding in 2-nitrophenol

Question 3

Preparation of alcohols

Answer 3

• Electrophilic addition from alkene
• Nucleophilic substitution from halogenoalkane
• Reduction from carbonyl compounds
• Reduction from Carboxylic acid

Question 4

Reactions of alcohols

Answer 4

• Combustion
• Reaction with Na(s)
• Formation of ester using Carboxylic acid or acid chloride
• Nucleophilic substitution to form halogenoalkanes
• Elimination of H₂O to form alkene
• Oxidation using KMnO₄ or K₂Cr₂O₇
• Tri-iodomethane

Question 5

What determines the strength of acid
- order of acidity of phenol, water, ethanol

Answer 5

• the stability of the anion formed from the acid
• more stable the anion, the stronger the acid
• phenol>water>ethanol

Question 6

Acidity of ethanol

Answer 6

• ethyl group is electron donating
• this intensifies the negative charge on the anion
• destabilizing the ethoxide ion
• dissociation of ethanol to release H⁺ is less favoured

Question 7

Acidity of phenol

Answer 7

• the lone pair of electrons on oxygen in the phenoxide anion is delocalised into the pie electron cloud of the benzene ring
• disperses the negative charge
• phenoxide ion is resonance destabilised
• dissociation of phenol to release H^{+ is favoured}

Question 8

Type of substituents on acidity in alcohols(electron-wiithdrawing group or electron donating group)

Answer 8

• electron-withdrawing group disperses the negative charge
• stabilises anion
• increase acid strength
• electron-donating group intensifies the negative charge
• destabilise anion
• decreases acid strength

Question 9

Strength of electron-withdrawing effect on acidity in alcohols

Answer 9

• more electronegative atom have stronger electron withdrawing effect
• disperses the negative charge to a greater extent
• stabilises anion to a greater extent
• increases acid strength

Question 10

Number of electron-withdrawing groups on acidity in alcohols

Answer 10

• greater number of electron-withdrawing groups
• stronger electron-withdrawing effect
• disperses the negative charge to a greater extent
• increases acid strength

Question 11

Position of electron-withdrawing effect on acidity in alcohols

Answer 11

• closer distance between the electron-withdrawing group and the (-O^-)
• disperses the negative charge to a greater extent
• stabilises anion to a greater extent
• increases acid strength

Question 12

Position of electron-withdrawing effect on acidity in alcohols

Answer 12

• closer distance between the electron-withdrawing group and the (-O^-)
• disperses the negative charge to a greater extent
• stabilises anion to a greater extent
• increases acid strength

Question 13

Type of substituent on acidity in phenols

Answer 13

• electron-withdrawing group increases the extent of delocalisation of lone pair of electrons on O^-
• disperses the negative charge to a greater extent
• stabilises anion to a greater extent
• increases acid strength
• electron-donating group decreases extent of delocalisation of lone pair of electrons on O^-
• disperses the negative charge to a smaller extent
• stabilises anion to a smaller extent
• decreases acid strength

Question 14

Strength of electron-donating or electron withdrawing effect in phenols

Answer 14

• stronger electron-withdrawing effect increases the extent of delocalisation of lone pair of electrons on O^-
• disperses the negative charge to a greater extent
• stabilises anion to a greater extent
• increases acid strength
• stronger electron-donating effect decreases the extent of delocalisation of lone pair of electrons on O^-
• disperses the negative charge to a smaller extent
• stabilises anion to a smaller extent
• decreases acid strength

Question 15

Number of substituents on acidity in phenols

Answer 15

• greater number of electron-withdrawing groups
• stronger electron-withdrawing effect
• increases the extent of delocalisation of lone pair of electrons on O^-
• disperses the negative charge to a greater extent
• stabilises anion to a greater extent
• increases acid strength

Question 16

Reactions of phenols

Answer 16

• Reaction with sodium metal
• Reaction with strong base
• Reaction with acid chlorides
• Electrophilic substitution reactions
  — nitration(mono-substitution, tri-substitution)
  — bromination(mono-substitution, tri-substitution)