RI 2025 Hydroxy Cpds Tutorial - Anwers to Discussion Questions

-1- Tutorial 18 – Hydroxy Compounds (Suggested Solutions) Practice Questions 1 Relative acidity: methylpropan-2-ol < ethanol < water < 2-methylphenol < phenol < 2-nitrophenol Methylpropan-2-ol and ethanol are alcohols while 2-methylphenol and 2-nitrophenol are substituted phenols. The more stable the conjugate base, the more acidic the compound. Alcohols are less acidic than water.  Alkoxide ion, RO , is less stable than hydroxide ion, OH –, due to the electron-donating alkyl group which intensifies the negative charge on the oxygen atom. Methylpropan-2-ol is less acidic than ethanol.  (CH 3)3CO has more electron-donating alkyl groups than CH 3CH2O that further intensifies the negative charge on the oxygen atom.  Thus (CH 3)3CO is less stable than CH3CH2O Phenols are more acidic than water.  The p-orbital containing the lone pair of electrons on the oxygen atom of the phenoxide ions overlaps with the  electron cloud of the benzene ring and the lone pair of electrons is delocalised into the ring.  This results in the delocalisation of negative charge on oxygen into the ring, i.e. dispersal of the negative charge over the ring.  Thus, the phenoxide ion is resonance–stabilised and more stable than hydroxide ion. 2-methylphenol is less acidic than phenol.  Presence of electron-donating group, CH3, on the benzene ring intensifies the negative charge on the oxygen atom.  Thus is less stable than . 2-nitrophenol is more acidic than phenol.  Presence of electron-withdrawing group, NO2, on the benzene ring disperses the negative charge on the oxygen atom.  Thus is more stable than . 2 Reagents Condition Structure T ype of reaction (a) sodium room temp Redox (b) sodium hydroxide room temp Acid-Base (c) sodium carbonate NA NO REACTION NA

-2- (d) phosphorus (V) chloride room temp, (anhydrous) Nucleophilic Substitution (e) hydrogen bromide dry HBr, heat Nucleophilic substitution and Electrophilic Addition Note:  Benzylic carbocation intermediate is more stable.  Without heating, only electrophilic addition of C=C occurs. (f) ethanoic acid conc. H2SO4, heat Condensation (esterification) (g) ethanoyl chloride room temp. Condensation (acylation) (h) aqueous bromine room temp. Electrophilic Substitution and Electrophilic Addition Note:  Benzylic carbocation intermediate is more stable. (i) bromine in CCl4 room temp. (or 2- or 4-substituted product) Electrophilic Substitution and Electrophilic Addition (j) potassium manganate (VII) KMnO 4(aq), H2SO4(aq), heat Vigorous oxidation (Oxidative cleavage of the C=C)

-3- 3 (a) Test Add Br2 (in CCl4) dropwise to each sample in a test-tube at room temperature, in the absence of uv light. Observations  For C 6H5CH=CH2, there is (rapid) decolourisation of orange-red Br2. C6H5CH=CH2 + Br2  C6H5CHBrCH2Br  For C 6H5CH2CH2OH, there is no