H2 Organic Chemistry Summary 2026

1 1. Types of Organic reaction you need to know Types of reaction Sub Reaction Comments Substitution (carbon centre is saturated/ resonance stabilised) Free Radical Substitution Homolytic fission of alkane leading to unpaired eln. H2 Topic: Alkane Electrophilic Substitution Electrophilic: reacting carbon-centre is eln rich; thus it attacks electrophile. H2 Topic: Arene Nucleophilic Substitution Nucleophilic: reacting carbon centre is eln poor; thus attacked by nucleophile. H2 Topic: Halogenoalkane Addition (carbon centre is unsaturated) Electrophilic Addition Electrophilic: C=C double bond is eln rich, thus it attacks electrophile. H2 Topic: Alkene Nucleophilic Addition Nucleophilic: reacting carbon centre is eln poor, thus attacked by nucleophile. H2 Topic: Carbonyl compound Oxidation Either increase in O atom/ decrease in H atom/ increase in OS Reduction Either decrease in O atom/increase in H atom/ decrease in OS Acid base reaction Bronsted Lowry Bronsted Acid donates H+. Bronsted Base accepts H+ Lewis Lewis acid accepts eln pair; Lewis base donates eln pair Hydrolysis Reaction whereby a molecule is cleaved into two molecules by H2O. Eg: Esters hydrolysis, Amide hydrolysis, Acid chlorides hydrolysis, Nitrile hydrolysis. Condensation Reaction between two functional groups to eliminate a small molecule such as water or ammonia. (one of these molecules involve a −C=O group) Eg. Carboxylic acid + alcohol, acid chloride + ammonia, etc) Elimination Reaction to remove a small molecule from an organic molecule (eg. Removal of HX from halogenoalkane; H2O from alcohol) Precipitation Chemical reaction that cause formation of solid from two aq. Soln. ** for reactions in italic, you need to know the mechanism.

2 2. Common reagents for synthesis Reagents & Condition Type of reaction Functional group Observations Products √ ? Section A: Oxidation KMnO4 with H2SO4 (aq), heat Or KMnO4 with NaOH, heat, followed by acidification KMnO4 with H2SO4 (aq), heat Oxidation (Oxidative cleavage) C H H Terminal alkene Decolourisation of purple soln; Effervescence observed. CO2 + H2O C R H Decolourisation of purple soln RCO2H formed. CH3CH=CH2 + 5[O] → CH3CO2H + H2O + CO2 Note: So if elucidation abt vigorous oxidation of alkene shows an increase of 2 O, the alkene contains this feature. C R R' Ketone formed. (CH3)2C=CH2 + 4[O] → (CH3)2CO + H2O + CO2 Note: So if elucidation abt vigorous oxidation of alkene shows an increase of 1 O, the alkene contains this feature. Oxidation (Side chain oxidation- occurs when C directly bonded to benzene ring has a H or O directly attached) CH3 Benzoic acid formed. C6H5CH3 + 3[O] → C6H5CO2H +H2O C H R R Decolourisation of purple soln; Effervescence observed. Benzoic acid formed. The rest of the chain get oxidised to CO2 & H2O unless question says otherwise C R O Benzoic acid formed. C6H5COCH3 + 4[O] → C6H5CO2H +H2O + CO2 Note: Likely to be hinted by the question

3 C OH R R Benzoic acid formed. Note: Likely to be hinted by the question Oxidation Aldehydes, 1° and 2°alcohols Decolourisation of purple soln Aldehyde → carboxylic acid 1° alcohol → carboxylic acid 2° alcohol → ketone 3° alcohol → no [O] Note: If elucidation shows a gain of 1 O atom during oxidation => likelihood is 1° alcohol Methanoic acid Ethanedioic acid Decolourisation of purple soln Effervescence observed. CO2 + H2O produced Dilute KMnO4 with NaOH (aq) Mild Oxidation Alkenes Decolourisation of purple soln Formation of brown MnO2 Alkene → Diol CH2=CH2 + H2O + [O] → CH2(OH)CH2OH K2Cr2O7 with H2SO4 (aq), Heat, Oxidation Aldehydes, 1° and 2°alcohols Orange soln turns green Aldehyde → carboxylic acid 1° alcohol → carboxylic acid (with reflux) 1° alcohol → aldehyde (with distillation) 2° alcohol → ketone Tollen’s reagent (ammonical solution of silver nitrate), Warm Aldehydes Silver mirror formed. Ag+ reduced to Ag RCHO + 2[Ag(NH3)2]+ + 3OH─ → RCO2─ + 2Ag + 4NH3 +2H2O Fehling’s Soln (alkaline solution of Copper(II) tartrate), warm Aliphatic Aldehydes only Reddish brown soln formed. Cu2+ reduced to Cu+ in Cu2O RCHO + 2 Cu2+ + 5OH─ → RCO2─ + Cu2O + 3H2O I2(aq) with NaOH, Warm Ethanol/Alcohols with the structural feature Yellow crystals of triiodomethane (CHI3) formed. RCH(OH)CH3 + 4I2 + 6OH─ → RCO2─ + CHI3 + 5I─ + 5H2O RCOCH3 + 3I2 + 4OH─ → RCO2─ + CHI3 + 3I─ + 3H2O

4 C CH3 OH H Or ethanal/ketones with the structural feature C CH3 O Synthesis to decrease carbon chain by 1 C. Section B: Reduction H2(g) with Ni catalyst Reduction Alkenes Aldehydes Ketones Nitriles - Alkene → Alkane Aldehyde → 1° alcohol Ketone → 2° alcohol * 1 mol of H2 reacts with 1 mol of the above Nitrile → Amine * 2 mol of H2 reacts with 1 mol of the above LiAlH4 in dry ether Reduction Aldehydes Ketones Nitriles Carboxylic acids Amides Aldehyde → 1° alcohol Ketone → 2° alcohol Nitrile → Amine Carboxylic acid → 1° alcohol Amide → Amine + H2O 1. RCONH2 + 4[H] → RCH2NH2 (1° amine) + H2O 2. RCONHR + 4[H] → RCH2NHR(2° amine) + H2O 3. RCONR2 + 4[H] → RCH2NR2 (3° amine) + H2O Note: LiAlH4 only reduce polar bonds, but not nitrobenzene. It may reduce esters to alcohols, if question give context. Sn with concentrated HCl, heat Followed by aq. NaOH, Nitrobenzenes Phenylamine produced.

5 Note: NaOH is added in 2 nd step to neutralise C 6H5NH3+ to liberate phenylamine. Section C: Reaction with Na/NaOH/NaHCO3/Na2CO3 Na(s) Redox reaction Alcohols Phenols Carboxylic acids Effervescence of H2 gas ROH + Na → RO─Na+ + ½ H2 C6H5OH + Na → C6H5O─Na+ + ½ H2 CH3CO2H + Na → CH3CO2─Na+ + ½ H2 Note: ½ mol of H2 liberated per mol of the organic molecule Na is oxidised, H is reduced. NaOH (aq) Acid base reaction Phenols Carboxylic acids Partition of phenols and carboxylic acids from organic layer into the aq. Layer Phenols → Phenoxide + water Carboxylic acids → Carboxylate salts + water. NaOH(aq), heat Nucleophilic Substitution/ or alkaline hydrolysis Halogenoalkanes (where X= Cl, Br, I) - Alcohols RX + OH─ → ROH + X─ To distinguish the diff halogenoalkanes, Dil HNO3 is added to remove the xs. NaOH, cooled and AgNO3 added in to precipitate AgX AgCl: White ppt AgBr: Cream ppt AgI: Yellow ppt Alkaline hydrolysis Amides Pungent alkaline gas liberated that turn moist red litmus blue Ammonia/ Amine produced with carboxylate salt RCONH2 + OH─ → RCO2─ + NH3 RCONHR + OH─ → RCO2─ + NH2R (NH2R might exist as a gas, either CH3NH2 or hinted by qns)

6 Nitriles RCN + OH─ +H2O → RCO2─ + NH3 Esters - Carboxylate salt and alcohol (or phenoxide salt) Note: 1. phenol deprotonate in presence of aq. NaOH to give phenoxide salt. 2. As water is used in hydrolysis, if need to carry out subsequent test to verify the starting c ompound is indeed ester, cannot use reagents such as PCl 5, SOCl 2 etc as they will get destroyed by the moisture from hydrolysis. Na2CO3(aq), NaHCO3(aq) Acid-base reaction Carboxylic acids Acyl Halides (where X= Cl, Br) Effervescence Carboxylic acid → Carboxylate salt + CO2 + H2O CH3COX → Carboxylate salt + NaX + H2O NaOH (ethanol), heat Elimination Halogenoalkanes Alkene C CC H H H CH3 H HXH C C CH3 H H CH3 C C CH2CH3 HH H HX (Both cis/trans) Note: Elimination is only possible if halogen and hydrogen atom are attached on adjacent carbons. Section D: Hydrolysis Dilute acids (HCl, HNO3, H2SO4), Heat Acid Hydrolysis Nitriles Amides Esters RCN + H+ + 2H2O → RCO2H + NH4+