VJC 2025 J2 H2 Chemistry Hydroxy Compounds Notes& Tutorial Student

VICTORIA JUNIOR COLLEGE CHEMISTRY DEPARTMENT Mr Tan Yong Khai/tan.yong.khai@vjc.edu.sg JC2 H2 CHEMISTRY HYDROXY COMPOUNDS (ALCOHOLS & PHENOLS) Lecture 1 2 Pages 1 – 9 10 – 14 Complete by T1W5 T1W5 Tutorial questions 1 – 3 4 – 7 ______________________________________________________________________________ LECTURE OUTLINE 1 Alcohols 1.1 Introduction (Nomenclature/Structure) 1.2 Physical Properties 1.2.1 Boiling point 1.2.2 Solubility 1.2.3 Acidity 1.3 Laboratory Preparation 1.3.1 From Alkenes 1.3.2 From Nucleophilic Substitution of Halogenoalkanes 1.3.3 From Reduction of Carboxylic Acids 1.3.4 From Reduction of Aldehydes and Ketones 1.4 Reactions 1.4.1 Complete Combustion 1.4.2 Nucleophilic Substitution to Halogenoalkanes 1.4.3 Redox (Acid-Metal) Reaction with Sodium 1.4.4 Oxidation to Carbonyl Compounds and Carboxylic Acids 1.4.5 Dehydration to Alkenes 1.4.6 Condensation to Esters 1.4.7 Tri-Iodomethane (Iodoform) Formation 2 Phenols 2.1 Introduction 2.2 Physical Properties 2.2.1 Appearance 2.2.2 Boiling point 2.2.3 Solubility 2.2.4 Acidity 2.3 Reactions 2.3.1 Reaction of the Hydroxy Group 2.3.2 Electrophilic Substitution at Benzene Ring 2.3.3 Reaction with Neutral FeCl3(aq) 3 Summary

2 REFERENCES 1 Modern Organic Chemistry by R.O.C. Norman and D.J.Waddington 2 Principles of Organic Chemistry by Peter R.S. Murray 3 A-Level Chemistry by E.N. Ramsden 4 Chemistry in Context by Hill and Holman LEARNING OUTCOMES Candidates should be able to: (a) recall the chemistry of alcohols, exemplified by ethanol: (i) combustion (ii) nucleophilic substitution to give halogenoalkanes (iii) reaction with sodium (iv) oxidation to carbonyl compounds and carboxylic acids (v) dehydration to alkenes (b) suggest characteristic distinguishing reactions for the different classes of alcohols ( primary, secondary and tertiary alcohols), e.g. mild oxidation (c) deduce the presence of a CH3CH(OH)– group in an alcohol from its reaction with alkaline aqueous iodine to form tri-iodomethane (d) recall the chemistry of phenol, as exemplified by the following reactions: (i) with bases (ii) with sodium (iii) nitration of, and bromination of, the benzene ring (e) explain the relative acidities of water, phenol and ethanol in aqueous medium (interpret as Brønsted-Lowry acids)

Alcohols Victoria Junior College 1 1 Alcohols 1.1 Introduction (Nomenclature/Structure) Nomenclature  General formula of CnH2n+1OH or CnH2n+2O.  Ending ‘−e’ of corresponding alkane is replaced by the suffix ‘−ol’.  Position of –OH group in carbon chain is specified by inserting the appropriate number between the stem of the name and the ‘−ol’.  When choosing the parent of an alcohol, identify the longest chain that includes the carbon atom connected to the –OH group.  When numbering the parent chain of an alcohol, the C atom to which the –OH group is attached to should receive the lowest number possible. Example: • Longest carbon chain bearing the -OH group is 6 carbons. The -OH group is attached to carbon 2 (not carbon 5) of this chain. Thus, the parent compound is hexan-2-ol. • There is a methyl group (-CH3) attached to carbon 5 of the chain. Thus, the full name of this compound is 5-methylhexan-2-ol. Exercise 1 Name the following alcohols. CH3CH2OH ethanol 2-methylpropan-2-ol 3-methylbutan-2-ol butan-2-ol methane methanol

Alcohols Victoria Junior College 2  Primary, secondary and tertiary alcohols type of alcohol number of alkyl groups on C to which OH is attached to primary (1°) 1 secondary (2°) 2 tertiary (3°) 3 Exercise 2 Classify the following alcohols as primary, secondary or tertiary. secondary primary tertiary secondary primary tertiary 1.2 Physical Properties 1.2.1 Boiling Point  Compared to alkanes of similar Mr, alcohols have higher boiling points. This is because there are intermolecular hydrogen bonds between alcohol molecules, which are stronger than instantaneous dipole – induced dipole interactions between alkane molecules, and require more energy to overcome. compound molecular formula boiling point/ oC methane CH4 -161.5 methanol CH3OH 64.5

Alcohols Victoria Junior College 3  Factors affecting boiling points: (i) Number of electrons in the molecule: Boiling point of alcohol increases with number of electrons as more energy is required to overcome the stronger instantaneous dipole-induced dipole interactions. alcohol molecular formula boiling point/ oC methanol CH3OH 64.5 ethanol CH3CH2OH 78.4 propan-1-ol CH3(CH2)2OH 97.0 (ii) Degree of branching: For constitutional isomers, b oiling point of alcohol decreases with greater degree of branching as molecule becomes more spherical and less energy is required to overcome the weaker instantaneous dipole -induced dipole interactions due to lower surface area for electron interactions. alcohol molecular formula boiling point/ oC butan-1-ol CH3(CH2)3OH 118 2-methylpropan-1-ol (CH3)2CHCH2OH 108 1.2.2 Solubility  Shorter chain alcohols (C 1 to C 3) are miscible with (are able to mix with) water due to their ability to form hydrogen bonds with water molecules.  As the hydrocarbon chain length of the alcohol increases, the miscibility decreases because the energy released from forming hydrogen bonds with water molecules is insufficient to overcome the increasingly strong er instantaneous dipole -induced dipole interactions between the alkyl chains, and existing hydrogen bonds between water molecules. 1.2.3 Acidity  Alcohols can behave as an acid by donating protons: ROH ⇌ RO− + H+ (1)  Alcohols are weaker acids than water; an aqueous solution of alcohol is neutral.  The lower acidity of alcohol is due to the destabilisation of alkoxide anion (RO-) by charge intensification.  The alkyl group (–R) exerts a stronger electron-donating inductive effect than the H atom.  This intensifies the negative charge on the oxygen atom in alkoxide ion and causes alkoxide ion to be less stable than hydroxide ion.  Alkoxide ion is formed less readily and position of equilibrium (1) lies to the left.

Alcohols Victoria Junior College 4 1.3 Laboratory Preparation Alcohols can be synthesised from alkenes, halogenoalkanes, carboxylic acids or carbonyl compounds (aldehydes or ketones). reagent condition type of reaction remarks alkenes concentrated H2SO4 followed by H2O (l), warm Industrial synthesis of alcohols from alkenes: steam, H3PO4 catalyst, high temperature and pressure electrophilic addition Remember to use Markovnikov’s rule to predict the major product formed when steam adds to alkenes. example: halogenoalkanes aqueous NaOH, heat nucleophilic substitution example: carboxylic acids lithium aluminium hydride (LiAlH4) in dry ether reduction Forms primary alcohols as a product. example: aldehydes • lithium aluminium hydride (LiAlH4) in dry ether, or • sodium borohydride (NaBH4) in methanol, or • H2 gas, Pt catalyst/Ni catalyst with heat reduction Forms primary alcohols as a product. example:

Alcohols Victoria Junior College 5 ketones • lithium aluminium hydride (LiAlH4) in dry ether, or • sodium borohydride (NaBH4) in methanol, or • H2 gas, Pt catalyst/Ni catalyst with heat reduction Forms secondary alcohols as a product. example: Exercise 3 Draw the structure of the compound formed by the reduction of the following carbonyl compounds. Exercise 4 What is the structural formula of the compound formed when CH2CHCH2CHO re