Organic chemistry is a significant portion of H2 Chemistry. This guide covers all the reactions you need to know.
Introduction to Organic Chemistry
Organic chemistry studies carbon compounds. In H2 Chemistry, you’ll learn about:
- Functional groups
- – Reaction mechanisms
- – Synthesis pathways
- – Isomerism
Functional Groups
Know these functional groups:
- Alkanes: C-C single bonds
- – Alkenes: C=C double bonds
- – Alcohols: -OH
- – Halogenoalkanes: -X (Cl, Br, I)
- – Aldehydes: -CHO
- – Ketones: C=O (middle of chain)
- – Carboxylic acids: -COOH
- – Esters: -COO-
- – Amines: -NH2
- – Amides: -CONH2
Alkanes
Reactions:
- Free Radical Substitution
- – With halogens (Cl2, Br2)
- – UV light needed
- – Multi-step mechanism
Steps:
- Initiation: X-X → 2X•
- – Propagation: X• + RH → HX + R•
- – Propagation: R• + X2 → RX + X•
- – Termination: various combinations
Alkenes
Reactions:
- Electrophilic Addition
- – With H2 (hydrogenation)
- – With H2O (hydration)
- – With HX (hydrohalogenation)
- – With X2 (halogenation)
Mechanism:
- Electrophile attacks double bond
- – Carbocation intermediate
- – Nucleophile attacks carbocation
Markovnikov’s Rule:
- H adds to carbon with more H
- – Major product prediction
2. Oxidation
- With KMnO4
- – Cleavage to carbonyls/acids
Halogenoalkanes
Reactions:
- Nucleophilic Substitution (SN1/SN2)
- – With OH- → alcohol
- – With CN- → nitrile
- – With NH3 → amine
SN1:
- Two-step mechanism
- – Carbocation intermediate
- – Tertiary halogenoalkanes
SN2:
- One-step mechanism
- – Concerted process
- – Primary halogenoalkanes
2. Elimination
- With OH- (alcoholic)
- – Forms alkene
Alcohols
Reactions:
- Combustion
- – Alcohol + O2 → CO2 + H2O
2. Oxidation
- Primary → aldehyde → carboxylic acid
- – Secondary → ketone
- – Tertiary → no reaction
Reagents:
- K2Cr2O7/H2SO4 (orange to green)
- – KMnO4 (purple to colourless)
3. Esterification
- Alcohol + carboxylic acid → ester
- – Concentrated H2SO4 catalyst
- – Reflux
4. Halogenation
- With HX, PCl5, SOCl2
- – Forms halogenoalkane
Carbonyl Compounds
Aldehydes:
- Oxidation to carboxylic acid
- – Reduction to alcohol
- – Nucleophilic addition
Ketones:
- No oxidation
- – Reduction to secondary alcohol
- – Nucleophilic addition
Tests:
- Fehling’s: aldehydes give brick red
- – Tollens’: aldehydes give silver mirror
- – 2,4-DNPH: both give orange ppt
Carboxylic Acids
Reactions:
- With bases
- – Acid + base → salt + water
2. With alcohols
- Acid + alcohol → ester + water
3. Reduction
- With LiAlH4 → alcohol
4. Acyl Chloride Formation
- With SOCl2 → acyl chloride
Derivatives:
- Acyl chlorides
- – Esters
- – Amides
Nitrogen Compounds
Amines:
- Basic properties
- – Salt formation
- – With acyl chlorides → amides
Amides:
- Neutral
- – Hydrolysis to carboxylic acid + amine
Amino Acids:
- Zwitterions
- – Isoelectric point
- – Peptide formation
Reaction Mechanisms
Know these mechanisms:
- Free radical substitution
- 2. Electrophilic addition
- 3. Nucleophilic substitution (SN1, SN2)
- 4. Nucleophilic addition
- 5. Elimination
Drawing Mechanisms:
- Show curved arrows
- – Include all intermediates
- – Show charges
- – Include stereochemistry if relevant
Synthesis Pathways
Learn to convert between functional groups:
Alkane → Halogenoalkane → Alcohol → Aldehyde → Carboxylic acid
↓
Ketone
Plan syntheses:
- Identify target molecule
- – Work backwards
- – Choose appropriate reagents
- – Consider conditions
Isomerism
Structural Isomerism:
- Chain isomerism
- – Position isomerism
- – Functional group isomerism
Stereoisomerism:
- Geometric (E/Z)
- – Optical (enantiomers)
Common Mistakes
- Wrong reagents/conditions
- 2. Incomplete mechanisms
- 3. Wrong products
- 4. Missing steps in synthesis
- 5. Not considering isomerism
How Ace Scorers Helps
Our H2 Chemistry programme covers:
- All organic reactions
- – Mechanism practice
- – Synthesis planning
- – Exam techniques
Contact us for H2 Chemistry tuition.
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