NJC 17A Alcohol (Student) 2026

National Junior College SH2 H2 Chemistry 1 7 HYDROXY COMPOUNDS

National Junior College SH2 H2 Chemistry 2 7A: Alcohols 7A.1 INTRODUCTION • Alcohols are organic compounds containing hydroxyl functional group (−OH). • General chemical formula of an aliphatic alcohol is CnH2n+1OH. • Aliphatic alcohols are also often represented as “R-OH” where R = alkyl groups. 7A.2 CLASSIFICATION AND NOMENCLATURE OF ALIPHATIC ALCOHOLS 7A.2.1 Classification There are 3 classes of aliphatic alcohols - differ in the no. of alkyl groups on the C atom to which –OH is attached. Type of Alcohol No. of alkyl groups on C atom to which –OH is attached to Primary (1°) 1 Secondary (2°) 2 Tertiary (3°) 3 Checkpoint 1 Classify each of the following aliphatic alcohols as a primary, secondary or tertiary alcohol. ___________________ __________________ ___________________ ___________________ ___________________ ___________________ R C OH H H R C OH R'' R' R C OH H R'

National Junior College SH2 H2 Chemistry 3 7A.2.2 Nomenclature • Alcohols are named by replacing the terminal ‘ -e’ of the corresponding alkane by ‘-ol’. • The parent chain must be the longest chain containing the –OH group. • The carbon with the –OH attached is given the lowest number possible. • Substituents are numbered according to their position on the parent chain, and listed in alphabetical order. • If more than one –OH group is present, the terms, di and tri are used, together with their respective numbers. Checkpoint 2 Fill in the correct structural formula of the alcohol. (a) (b) (c) Propane-1,3-diol 2-methylpropan-2-ol 2-ethylcyclohexanol Negative effects of excessive alcohol consumption (FYI) In Singapore, binge drinking (defined as having four or more alcoholic drinks in one session for women, and five or more for men) is most common among 18- to 29-year-olds: 18.7% of men and 12.2% of women. In 2010, the Singapore Mental Health Study found that about 3.5% of our citizens suffered from alcohol abuse at some point in their lives and 0.5% from alcohol addiction (or alcoholism).1 Alcohol is eliminated from the body by various metabolic mechanisms. In general, alcohol metabolism is achieved by both oxidative and non-oxidative pathways. A person’s brain develops until the age of about 24. During this time, alcohol abuse can result in learning difficulties and social problems. Alcohol is also a known cause of cancers of the mouth, throat (pharynx), voice box (larynx), oesophagus, liver, co lon and rectum, and breast. 3 Alcohol may increase the risk of cancer of the pancreas too. For each of these cancers, the risk increases with the amount of alcohol consumed. The exact way alcohol affects cancer risk isn’t completely understood. In fact, there might be several different ways it can raise risk, and this might depend on the type of cancer. 1 Health Promotion Board and National Addictions Management Service (2012). When does drinking become a problem? Retrieved from http://www.nams.sg/resources/Documents/Problem%20Drinking%20Resource%20Booklet.pdf 2 Zakhari, S. (n.d.). Overview: How is alcohol metabolized by the body? Retrieved from http://pubs.niaaa.nih.gov/publications/arh294/245-255.htm 3 American Cancer Society. Retrieved from http://www.cancer.org/index

National Junior College SH2 H2 Chemistry 4 7A.3 PREPARATION OF ALCOHOLS Success Criteria: • I can state the reagents and conditions to convert various functional groups to alcohol. • I know that LiAlH4 cannot reduce C=C. • I know that LiAlH4 is the only reducing agent that can reduce RCOOH. Checkpoint 3 Fill in the blanks. Reactant Reagents and conditions Major Product Type of Reaction Steam, conc H3PO4, Heat, high pressure Electrophilic addition conc H2SO4, room temp, followed by warm with H2O NaOH(aq), heat Nucleophilic substitution (industrial method)

National Junior College SH2 H2 Chemistry 5 Note: LiAlH4 is the only reducing agent that can reduce carboxylic acid. 7A.3.1 Reduction of Carbonyl Compounds (Aldehydes and Ketones) and Carboxylic Acids There are several reducing agents which will be covered in the A level syllabus. However, not all reducing agents will work on all functional groups. Heterogeneous catalysis such as Pt and Ni may be used to reduce alkenes and carbonyl compounds, but is not suitable for carboxylic acid. The table below summarizes the reducing agents/conditions and the organic compounds that can be reduced to alcohols. Carboxylic acid Ketone Aldehyde LiAlH4 in dry ether, room temperature ✓ ✓ ✓ H2 with Ni catalyst or H2 with Pt catalyst  ✓ ✓ Note: −COOH group in carboxylic acid is resonance stabilized. Hence we need a stronger reducing agent to reduce the −COOH group. Note: Aldehydes are reduced to their corresponding primary alcohols, while ketones are reduced to their corresponding secondary alcohols. Carboxylic acids and aldehydes are reduced to primary alcohols but ketones are reduced to secondary alcohols. Organic compounds Reducing agent/ conditions

National Junior College SH2 H2 Chemistry 6 Note: In A level questions, you are to use [H] to represent the reducing agent, LiAlH4 to balance the equations. Other atoms in the equation are balanced using H2O. Note: H− from LiAlH4 is an nucleophile and does not react with electron rich C=C because the C=C bond lacks an electrophilic carbon for nucleophilic attack. Checkpoint 4 Fill in the blanks provided. Place a ‘✓’ next to the reducing agent which allows the reduction to be carried out. CH3 C O H + [H] CH3 C OH H H  LiAlH4 in dry ether  H2/Ni  LiAlH4 in dry ether  H2/Ni  LiAlH4 in dry ether  H2/Ni + [H]O OH  LiAlH4 in dry ether  H2/Ni + [H]O OH  LiAlH4 in dry ether  H2/Ni Alternative form of fuel: Bioethanol A biofuel is an organic compound made by or from a living organism, which humans can use to power something. In practical consideration, any organic fuel that is produced from organic matter (living or once-living material) in a short period of time (days, weeks or even months) is a biofuel. This contrasts with fossil fuels, which take millions of years to form, and with other types of fuel, which are not based on organic compounds (nuclear fission, for instance). Bioethanol is an alcohol made by fermentation, mostly from carbohydrates in the form of suga r and starch produced by crops such as corn and sugarcane. However, there are concerns about the production of bioethanol, such as the fact that it requires more energy for production than it can supply and that it directly competes for land for growing crops. H2

National Junior College SH2 H2 Chemistry 7 7A.4 CHEMICAL REACTIONS OF ALCOHOLS Success Criteria: 1. I am able to give the reagents and conditions for different types of reactions involving alcohol and the structure of products formed. 2. I know that C −O bond is cleaved when alcohol undergoes elimination and substitution reaction while O−H bond is cleaved when alcohol are involved in (i) redox reaction (ii) reaction when O in alcohol is the nucleophile e.g. esterification. 3. I know that alcohol is not acidic in aqueous medium due to the RO− more unstable (stronger base) than OH−. 4. I am able to state the 2 different sets of reagent s and conditions for formation of ester, and able to explain their difference in reactivity and yield. 5. I know that C―OH (BE: 360 kJmol−1) bond in alcohol cannot be substituted by Cl−, Br− ion to form C ―X bond (BE (C ―Cl): 340 kJmol −1 BE(C―Br): 280 k