Alcohols, Phenols and Ethers

Alcohols and phenols are formed when a hydrogen atom in a hydrocarbon (aliphatic or aromatic) is replaced by an -OH group, while ethers contain an R-O-R' linkage. In this chapter you will learn the classification and IUPAC nomenclature of these compounds, the structure of their functional groups, and methods of preparation: alcohols from alkenes by acid-catalysed hydration and hydroboration-oxidation, by reduction of aldehydes, ketones and acids, and from Grignard reagents; and phenols from haloarenes, benzene sulphonic acid, diazonium salts and cumene. You will explain their high boiling points and solubility in terms of hydrogen bonding. The chapter then explains chemical reactions: the acidity of alcohols and phenols and the effect of electron-withdrawing and electron-releasing groups, esterification, reactions with hydrogen halides including the Lucas test, dehydration, and oxidation with PCC. You will study electrophilic substitution in phenol (nitration, bromination), Kolbe's reaction and the Reimer-Tiemann reaction, the industrial preparation of methanol and ethanol, and the preparation of ethers by Williamson synthesis, their cleavage by HI, and electrophilic substitution in anisole.

Detailed Worksheet: Alcohols, Phenols and Ethers Section A - Definitions (10 marks) 1. Classify the following as primary, secondary or tertiary alcohols: CH3CH2OH, (CH3)2CHOH, (CH3)3COH, and give the IUPAC name of each. (2 marks) 2. What is the Lucas test? How does it distinguish between primary, secondary and tertiary alcohols? (2 marks) 3. What is the Reimer-Tiemann reaction? Write the equation for phenol. (2 marks) 4. What is Williamson synthesis? Why is a primary alkyl halide preferred in it? (2 marks) 5. What is denatured alcohol? Why is ethanol denatured? (2 marks) Section B - Calculations and Applications (15 marks) 6. 9.2 g of ethanol reacts completely with sodium metal according to 2C2H5OH + 2Na -> 2C2H5ONa + H2. Calculate the moles of ethanol used and the volume of hydrogen evolved at STP (molar volume 22.4 L; C = 12, H = 1, O = 16). (3 marks) 7. 4.7 g of phenol is treated with excess bromine water. Write the balanced equation, and calculate the mass of 2,4,6-tribromophenol formed and the mass of bromine consumed (C = 12, H = 1, O = 16, Br = 80). (3 marks) 8. In the fermentation of glucose, C6H12O6 -> 2C2H5OH + 2CO2. Calculate the mass of ethanol and the volume of CO2 at STP obtained from 360 g of glucose. Name the enzymes that convert sucrose to glucose and glucose to ethanol. (3 marks) 9. Arrange in increasing order of acidity, giving reasons: phenol, ethanol, p-nitrophenol, p-cresol, water. Use the pKa values: ethanol 15.9, water 15.7, p-cresol 10.2, phenol 10.0, p-nitrophenol 7.1. (3 marks) 10. Write all the structural isomers of C4H10O. Classify them as alcohols or ethers and state how many of the alcohols are primary, secondary and tertiary. (3 marks) Section C - Diagrams (10 marks) 11. Draw the structures of methanol, phenol and methoxymethane showing bond angles (C-O-H 108.9 degrees in methanol, C-O-C 111.7 degrees in methoxymethane). Explain why the C-O bond length in phenol (136 pm) is shorter than in methanol (142 pm). (4 marks) 12. Draw the resonance structures of the phenoxide ion and explain why phenol is more acidic than ethanol. (3 marks) 13. Draw a flowchart showing the preparation of phenol from cumene, including the formation of cumene hydroperoxide and the products. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Explain the mechanism of acid-catalysed dehydration of ethanol to ethene at 443 K in three steps. Explain why ethanol at 413 K with concentrated H2SO4 gives ethoxyethane instead, and why tertiary alcohols dehydrate most easily. (5 marks) 15. Explain why ortho-nitrophenol is steam volatile while para-nitrophenol is not. Compare their boiling points and acidities, and explain why nitro groups at ortho and para positions increase the acidity of phenol more than at the meta position. (5 marks) 16. Predict the products when (i) methoxybenzene reacts with HI (ii) (CH3)3C-O-CH3 reacts with HI. Explain the mechanism in each case (SN1 or SN2), and explain why (CH3)3C-Br and sodium methoxide cannot be used to prepare (CH3)3C-O-CH3 by Williamson synthesis. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Write balanced chemical equations and show all structures clearly. Use the given atomic masses for calculations.