JPJC 2026 Intro to Organic Chemistry and Isomerism Tutorial Answer

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. Note: For displayed formula, all bonds, atoms and bond orders must be shown (bond angle is not required). For skeletal structure, all C−C and C–H bond must be hidden. (a) 3−phenylpropan−1−ol (b) 2−bromomethylbenzene C C C H H O H H H HH OH C H H H Br Br (c) 1−bromo−1,2,2−trichloropropane (d) 2,4−dimethylpenta−1,3−diene C C C H Br H H H Br Cl Cl Cl Cl Cl Cl C C C H C H C H H H C C H H H H H H H (e) hexane−1,6−dioic acid (f) 3−methylcyclopentanone C C C C C C O O H H H H H H H H H O O H OH O OH O O C C C C C O C H H H H HH H H H H This is displayed! Note: For benzene ring, there is no need to show all the C-C and C-H bonds in displayed formula unless stated otherwise.

2026 JC1 H2 Chemistry (9476) 2 Introduction to Organic Chemistry and Isomerism (g) ethyl propanoate (h) 2–methylheptanoyl chloride O O C C O O C C CH H H H H H H H H H C C C C C H H H H H H H C O CCH H H H H H H H O Cl Cl Naming of Organic Compounds 2 For each of the following compounds, give their IUPAC (systematic) names. (a) CH2ClCHClBr (b) CH3CHBrCHO 1−bromo−1,2−dichloroethane 2−bromopropanal (c) CH2(NH2)COOH 2−aminoethanoic acid Functional Group 3 For each of the following compounds, identify all the functional groups present. (a) OH O OH NH2 O phenol alkene ketone (primary) amine aldehyde (secondary) alcohol primary alcohol secondary alcohol tertiary alcohol Note: For alcohols, the classification (primary, secondary or tertiary) should be given. Br C C Cl Cl Br C C C O C COOH NH2 C C C C OH C H C C OH H H C C OH OH OH OH secondary alcohol primary amine

2026 JC1 H2 Chemistry (9476) 3 Introduction to Organic Chemistry and Isomerism (b) ClO NH2 O O O OH O (primary) amide ester carboxylic acid acyl chloride Reactions of Organic Compounds 4 Classify the following organic reactions as substitution, addition, elimination, condensation, hydrolysis, oxidation or reduction. (a) + Br2 Br + HBr A H atom on benzene is replaced with a Br atom (or no. of electron pairs/groups around reactive C remains unchanged) (or sp2 carbon to sp2 carbon)  (electrophilic) substitution (b) CH3CH=CHCH3 + Br2 → CH3CHBrCHBrCH3 2 molecules combined to give one product only (or no. of electron pairs/groups around reactive C increases) (or sp2 carbon to sp3 carbon)  (electrophilic) addition (c) CH3CHBrCHBrCH3 → CH2=CHCH=CH2 + 2HBr 2 units of small molecule HBr is removed (or no. of electron pairs/groups around reactive C decreases) (or sp3 carbon to sp2 carbon)  elimination

2026 JC1 H2 Chemistry (9476) 4 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 (C=C) and diol (two alcohols, two –OH groups) functional groups. K also has the following features: • No oxygen atom is attached to any carbon atom which is involved in a double bond.  cannot be O C=C • No carbon atom has more than one oxygen atom joined to it.  cannot be C O O 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. Thought process: • K, C4H8O2, has a C=C bond and two –OH groups. • K does not contain the following structures: Hence, the possible structures (constitutional isomers) of K are as follows: C C OH C OH OH C OH OH H H H H H C C C C H OH OH H H H H H C C C C H OH OH H H H C C C H OH H C H OH * This molecule can exhibit enantiomerism This molecule can exhibit cis-trans isomerism This molecule cannot exhibit stereoisomerism (no cis-trans isomerism and no enantiomerism)

2026 JC1 H2 Chemistry (9476) 5 Introduction to Organic Chemistry and Isomerism Type of stereoisomerism: cis–trans isomerism It has a C=C bond to restrict free rotation about the C=C bond and each C of C=C has 2 different groups of atoms attached. C C H C C H O H H H O HH H C C H C H C O H H H O HH H cis isomer trans isomer Type of stereoisomerism: enantiomerism It has a chiral carbon and has no plane of symmetry. C C C O H CH H H O H H H H C C C O H C H H H O H H H H a pair of enantiomers (or non-superimposable mirror images) * * The diagram must: • show 3D tetrahedral shape (with wedge & hash lines) at C* • label chiral carbon with ‘*’ • show dotted line to represent the mirror plane • label “non-superimposable mirror images” In addition, • displayed formula must be shown (all bonds must be shown) The diagram must: • show trigonal planar shape of >C=C< • label ‘cis’ and ‘trans’ (if applicable) In addition, • displayed formula must be shown (all bonds must be shown) non-superimposable mirror images cis-isomer trans-isomer

2026 JC1 H2 Chemistry (9476) 6 Introduction to Organic Chemistry and Isomerism 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. Substitution (Note: Br- is substituted by OH-.) 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. Nucleophile {the lone pair of electrons on :OH− will be donated to the C+} (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. {Butan-2-ol has a chiral carbon atom and no plane of symmetry  it can exhibit enantiomerism. Why is the mixture optically inactive?} State the type of stereoisomerism exhibited by butan -2-ol and draw appropriate diagrams to illustrate the stereoisomerism. Type of stereoisomerism: Enantiomerism : Nucleophiles are electron–rich species that can donate an electron pair and attack electron– deficient centre in an organic molecule. H H H H H C C C C H H H OH H * The product mixture is a racemic mixture which contains equal proportion of the two enantiomers. It is optically inactive since the rotating power of one enantiomer cancels that of the other and this results in no net rotation of the plane–polarised light.

2026 JC1 H2 Chemistry (9476) 7 Introduction to Organic Chemist