JPJC 2026 Intro to Organic Chemistry and Isomerism Annotated Tutorial

2026 JC1 H2 Chemistry (9476) 1 Introduction to Organic Chemistry and Isomerism Jurong Pioneer Junior College 2026 JC1 H2 Chemistry (9476) Organic Chemistry Topic 8: Introduction to Organic Chemistry and Isomerism Level 1 – Self–Check Questions Formulae of Organic Compounds 1 For each of the following compounds, draw the displayed (full structural) structure and the skeletal structure. (a) 3−phenylpropan−1−ol (b) 2−bromomethylbenzene (c) 1−bromo−1,2,2−trichloropropane (d) 2,4−dimethylpenta−1,3−diene (e) hexane−1,6−dioic acid (f) 3−methylcyclopentanone (g) ethyl propanoate (h) 2–methylheptanoyl chloride Naming of Organic Compounds 2 For each of the following compounds, give their IUPAC (systematic) names. (a) CH2ClCHClBr (b) CH3CHBrCHO (c) CH2(NH2)COOH Functional Groups 3 For each of the following compounds, identify all the functional groups present. (a) OH O OH NH2 O (b) ClO NH2 O O O OH O Reactions of Organic Compounds 4 Classify the following organic reactions as substitution, addition, elimination, condensation, hydrolysis, oxidation or reduction. (a) + Br2 Br + HBr (b) CH3CH=CHCH3 + Br2 → CH3CHBrCHBrCH3 (c) CH3CHBrCHBrCH3 → CH2=CHCH=CH2 + 2HBr

2026 JC1 H2 Chemistry (9476) 2 Introduction to Organic Chemistry and Isomerism Level 2 – Application Questions Isomerism 5 [N2011/P2/Q5(b) modified] Compound K has the molecular formula of C4H8O2 and it contains both alkene and diol functional groups. K also has the following features: • No oxygen atom is attached to any carbon atom which is involved in a double bond. • No carbon atom has more than one oxygen atom joined to it. Draw the displayed stereochemical formulae of all possible stereoisomers of K. For each structure you draw, state the type of stereoisomerism it shows and explain why they can exhibit the particular stereoisomerism. Reactions of Organic Compounds 6 2-bromobutane reacts with NaOH(aq) to give butan-2-ol. CH3CHBrCH2CH3 + OH− → CH3CH(OH)CH2CH3 + Br− (a) (i) Classify the type of organic reaction (substitution, addition, elimination, condensation, oxidation or reduction) that 2-bromobutane has undergone. The reaction between 2-bromobutane and NaOH(aq) proceeds via a 2-step mechanism as shown below. (ii) Step 1 involves heterolytic bond fission. In the diagram above, draw a curly arrow to complete the mechanism of the reaction in Step 1 . Show any charges, dipoles and any relevant lone pairs. (iii) State whether NaOH is acting as an electrophile or nucleophile in Step 2. (iv) Hence draw curly arrows in the diagram above to complete the mechanism of the reaction in Step 2. Show charges, dipoles and any relevant lone pairs. (b) The product mixture of butan-2-ol exists as a mixture of stereoisomers but the product mixture is optically inactive. State the type of stereoisomerism exhibited by butan -2-ol and draw appropriate diagrams to illustrate the stereoisomerism.

2026 JC1 H2 Chemistry (9476) 3 Introduction to Organic Chemistry and Isomerism Hybridisation 7 Allenes are a group of hydrocarbons in which one atom of carbon is connected by double bonds with two other carbon atoms. This makes allenes generally more reactive than alkenes. 1−phenylbuta−1,2−diene is an example of an allene. C C C H CH3 H 1 234 5 6 7 The structure of 1−phenylbuta−1,2−diene may be described in terms of the hybridisation of orbitals. (a) What are the hybridisation states each carbon atom from C−1 to C−7 in a molecule of 1−phenylbuta−1,2−diene? (b) Sketch the shape of the hybrid orbitals and state the bond angles around C−1, C−2 and C−3. Multiple Choice Questions Functional Groups 8 [N2011/P1/Q37] Swine flu has caused great concern internationally. One widely used treatment is the anti–viral drug Tamiflu. Tamiflu OCH2CH3 O OCH(CH2CH3)2 N H C O CH3 NH2 What statements about Tamiflu are correct? 1 It contains an amide group. 2 It contains two ester groups. 3 It contains four chiral centres. A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only 9 [N2013/P1/Q39 modified] A non–cyclic organic compound has the molecular formula C4H9O2N. Which pair of functional groups could be present in this molecule? 1 one ester group and one amine group 2 one carboxylic acid group and one nitrile group 3 one carboxylic acid group and one amine group A 1, 2 and 3 B 1 and 3 only C 2 and 3 only D 1 only

2026 JC1 H2 Chemistry (9476) 4 Introduction to Organic Chemistry and Isomerism Isomerism 10 [N2015/P1/Q21] The alkynes are a series of non–cyclic hydrocarbons with the general formula CnH2n−2 containing one carbon–carbon triple bond per molecule. How many constitutional isomers exist, that are alkynes, with five carbon atoms in their molecules? A 2 B 3 C 4 D 5 11 [N2004/P1/Q20] How many esters are there with the molecular formula C4H8O2? A 2 B 3 C 4 D 5 12 [N2016/P1/Q37] One molecule of a non –cyclic organic compound contains only carbon atoms, hydrogen atoms and one oxygen atom. The compound is a ketone and contains a chiral carbon atom. One molecule of this compound contains x carbon atoms. What could be the value of x? 1 5 2 6 3 7 A 1, 2 and 3 B 1 and 3 only C 2 and 3 only D 1 only 13 [N2015/P1/Q38] The red seaweed Chondrococcus hornemanni, which is found in the Pacific Ocean, contains a number of different halogenoalkenes with the same carbon skeleton which is shown below. In this structure, X, Y and Z each represent either a hydrogen or a bromine atom or a chlorine atom. C C H HZ CC Y H CH CH2 CH3 C C X CH3 CH3 Which could be the identities of atoms X, Y and Z for a compound to show cis–trans isomerism? X Y Z 1 Cl H Cl 2 H Br Cl 3 H Br H A 1, 2 and 3 B 1 and 3 only C 2 and 3 only D 1 only

2026 JC1 H2 Chemistry (9476) 5 Introduction to Organic Chemistry and Isomerism 15 [N2015/P1/Q40] Which molecules are optically active? 1 CH3 H CH3 OH 2 CH3 OH CH3 OH 3 CH3 H H CH3 A 1, 2 and 3 B 1 and 3 only C 1 and 2 only D 2 only 14 [N2013/P1/Q19] Yanucamide B can be extracted from a marine sponge. Yanucamide B O N H O O O N O N H O O Which combination of the number of chiral centres and of ester linkages does it possess? number of chiral centres number of ester linkages A 4 2 B 4 3 C 5 2 D 5 3

2026 JC1 H2 Chemistry (9476) 6 Introduction to Organic Chemistry and Isomerism 16 [RI Prelim 2012/P1/Q18 modified] A molecule has the structure shown below. OH How many possible stereoisomers exist for the molecule? A 29 B 210 C 211 D 212 Reactions of Organic Compounds 17 [N2015/P1/Q37] What are the characteristics of a free radical? 1 It always has an unpaired electron. 2 It always has a lone pair of electrons. 3 It can be formed by homolytic fission of a covalent bond. A 1, 2 and 3 B 1 and 3 only C 2 and 3 only D 1 only 18 [ACJC Prelim 2012/P1/Q21 modified] Ethanal can react with ammonia as shown. O + NH3 NH2 OH Which type of chemical reaction has occurred? A condensation B elimination C substitution D addition Hybridisation 19 [N2015/P1/Q22] Matricarin occurs in oil of chamomile. OCH3 O O CH3 CH3 OCOCH3 matricarin How many of its carbon atoms are sp2 hybridised? A 4 B 5 C 6 D 7

2026 JC1 H2 Chemistry (9476) 7 Introduction to Organic Chemistry and Isomerism 20 [N2012/P1/Q19] Covalent bonds are formed by orbital overlap. The shape of unsaturated hydrocarbon molecules can be explained in terms of hybridisation of orbitals. Which bond is not present in HCCCH2CH=CH2? A a  bond formed by 2p−2p overlap B a  bond formed by 1s−2sp overlap C a  bond formed by 2sp−2sp2 overlap D a  bond formed by 2sp2−2sp3 overlap 22 Liquid D has a molecular mass of 44. Its composition