2025 NYJC H2 Chem Hydroxy Compounds CE Ans

1 Nanyang Junior College Chemistry (9729) Consolidation Exercise 14 Hydroxy Compounds (Answers) JC2/2025 Name: Marks / 10 CT: 24 Tutor: 1 (a) State the type of reaction and draw the structural formula of the organic product formed when the following compounds reacts with each of the following reagent. [3] OH CH2OH (i) Hot acidified potassium dichromate(VI) O COOH [1] for structure Type of reaction: Oxidation (ii) Ethanoyl chloride, CH3COCl O C CH3 O O CH3 O [1] for structure Type of reaction: condensation / nucleophilic acyl substitution The acyl chor ide will reac t with both the alcohol groups [1] for type of reaction for both (i) and (ii)

2 (b) Draw the structure of the organic product formed when the following compound reacts with each of the following reagent. [2] OH OH (i) Aqueous bromine OH OH OH Br Br BrBr [1] (ii) Hot, alkaline potassium manganate(VII) O - O O - K + K + [1] Accept Na+/K +as counter ion or no counter ion. Phenol undergoes acid base reaction with the alkaline medium, while the carbon containing side chain of benzene undergoes oxidation. Note that the side pdt ethandioic acid will be further [O] to CO 2 and H2O; and turned to inorganic pdts CO32- and H2O. Explanation for 1b(i)

3 OH OH BrBr BrBr OH OH OH Br Br BrBr OH OH OH OH Br Br BrBr + + less stable, will not be formedmore stable benzylic carbocation , as the p orbital of the sp2 carbocation can overlap with the delocalised π electron cloud of the benzene ring. Br-Br Br-Br H2O

4 2 State how propan-1-ol and propan-2-ol could be distinguished by a simple chemical test . Give the observation and write equations for any reaction(s). Test: Add NaOH(aq), I2(aq), warm Observation: Yellow ppt of CHI3 formed for propan-2-ol, no yellow ppt for propan-1-ol (must state both positive and negative observations for both alcohols) [1] for test and observations Equation(s): OHC CH3 R H + CHI3+ H3C C O O-Na+ + 5H2O5NaI+CH3 4I2 + 6NaOH CH3 [1] for eqn propan-1-ol C CC H H H H O H H H H propan-2-ol C CH H H H O C H H H H 3 Explain why ethanol is a weaker acid than phenol in terms of the Bronsted-Lowry theory. [3] (Ethanol and phenol are Bronsted-Lowry acids as they are proton donors. Strength of the acid depends on the stability of the conjugate base) The ethoxide ion (C2H5O¯) is less stable than the phenoxide ion as the negative charge on the O atom is intensified by an electron donating alkyl group, hence destabilising it. Ethanol is therefore less acidic, and donates protons less readily and POE of the ethanol dissociation lies more to the left. The phenoxide ion is more stable as the p orbital of O overlaps with the π orbitals of benzene ring resulting in the delocalisation of lone pair of electrons on the O atom into the benzene ring. Negative charge on O atom is dispersed over the benzene ring and one oxygen atom, hence stabilising it. Therefore phenol is more acidic and it donates a proton more readily and POE of the phenol dissociation lies more to the right. total [3] for all 3 marking points: • stating that ethoxide ion is less stable than the phenoxide ion • explanation of stability of each conjugate base • stating the POE of dissocation of each acid