Organic Chemistry Refresher Course
1. Introduction
Organic chemistry is the study of carbon-based compounds and their reactions. Carbon forms four covalent bonds, allowing it to create:
Straight chains (aliphatic compounds)
Branched structures
Cyclic structures (aromatic and non-aromatic rings)
Unique properties of carbon:
Catenation: The ability to form long chains by bonding with itself.
Multiple bonds: Single, double, and triple bonds exist (C-C, C=C, C≡C).
Hybridization: Determines molecular shape (sp³, sp², sp).
Classification of Organic Compounds
| Category | Example | General Formula |
|---|---|---|
| Alkanes (saturated hydrocarbons) | Methane (CH₄), Ethane (C₂H₆) | CₙH₂ₙ₊₂ |
Alkenes (unsaturated, double bond) | Ethene (C₂H₄) | CₙH₂ₙ |
Alkynes (unsaturated, triple bond) | Ethylene (C₂H₂) | CₙH₂ₙ₋₂ |
Aromatic Compounds | Benzene (C₆H₆) | CₙHₙ |
Alcohols | Ethanol (C₂H₅OH) | R-OH |
| Carboxylic Acids | Acetic acid (CH₃COOH) | R-COOH |
| Amines | Methylamine (CH₃NH₂) | R-NH₂ |
| Ketones | Acetone (CH₃COCH₃) | R-CO-R' |
| Aldehydes | Formaldehyde (HCHO) | R-CHO |
2. Alkanes (Saturated Hydrocarbons)
General formula: CₙH₂ₙ₊₂
Single bonds only (sp³ hybridization) → tetrahedral geometry (109.5°)
Non-polar, insoluble in water, but soluble in organic solvents.
Example Reactions:
Combustion
CH4+2O2→CO2+2H2O+heatSubstitution (Halogenation)
CH4+Cl2→UV light CH3Cl+HCl3. Alkenes & Alkynes (Unsaturated Hydrocarbons)
Alkenes (C=C double bond, sp² hybridization)
General formula: CₙH₂ₙ
Planar geometry (120°)
Reactions:
Addition (Hydrogenation, Halogenation, Hydrohalogenation, Hydration)
Polymerization (formation of plastics like polyethylene)
Example: Ethene Reactions
Hydrogenation (converting alkene to alkane)
Halogenation (Bromine test for unsaturation)
C2H4+Br2→C2H4Br2Bromine water turns colorless → confirms presence of C=C bond.
Alkynes (C ≡ C triple bond, sp hybridization)
General formula: CₙH₂ₙ₋₂
Linear geometry (180°)
React similarly to alkenes but require two equivalents of reagents in addition reactions.
4. Aromatic Hydrocarbons (Benzene & Derivatives)
Benzene (C₆H₆) is a planar, cyclic compound with delocalized π-electrons, making it very stable.
Aromaticity Rules (Hückel’s Rule):
A molecule is aromatic if it has 4n+2 π-electrons (n = 0,1,2…).
Reactions of Benzene:
Benzene undergoes electrophilic substitution rather than addition:
Nitration (to make explosives like TNT)
- Toluene is reacted with a mixture of nitric acid (HNO3) and sulfuric acid (H2SO4) to produce mononitrotoluene (MNT).
- Reaction: C6H5CH3 (toluene) + HNO3 + H2SO4 → C6H4CH3NO2 (MNT) + H2O
- The MNT is then further nitrated with a mixture of nitric and sulfuric acids to form dinitrotoluene (DNT).
- Reaction: C6H4CH3NO2 (MNT) + HNO3 + H2SO4 → C6H3(CH3)(NO2)2 (DNT) + H2O
- The DNT is finally nitrated using a mixture of nitric acid and oleum (fuming sulfuric acid) to produce trinitrotoluene (TNT).
- Reaction: C6H3(CH3)(NO2)2 (DNT) + HNO3 + oleum → C6H2(CH3)(NO2)3 (TNT) + H2O
5. Functional Groups & Their Reactions
Alcohols (R-OH)
Hydrogen bonding → higher boiling points
Oxidation:
Primary alcohol → Aldehyde → Carboxylic Acid
Secondary alcohol → Ketone
Aldehydes & Ketones (R-CHO, R-CO-R’)
Aldehydes can be oxidized to carboxylic acids
Ketones resist oxidation
Tollens' test, also known as the silver mirror test, is a chemical test used to distinguish between aldehydes and ketones, where a positive result (presence of an aldehyde) is indicated by the formation of a silver mirror on the inner surface of the reaction vessel.
- Tollens' test uses Tollens' reagent, which is an alkaline solution of silver nitrate (AgNO3) and ammonia (NH3). How it works:
- Aldehydes are oxidized to carboxylic acids by Tollens' reagent, while the silver ions (Ag+) in the reagent are reduced to metallic silver (Ag).
- The reduced silver precipitates out of solution and forms a mirror-like coating on the inner surface of the reaction vessel, hence the name "silver mirror test".
- Ketones do not react with Tollens' reagent, so they do not produce a silver mirror.
- The reaction can be summarized as follows: RCHO + 2[Ag(NH3)2]+ + 3OH- → RCOO- + 2Ag + 4NH3 + 2H2O.
- RCHO represents the aldehyde.
- RCOO- represents carboxylic acid.
- RCHO represents the aldehyde.
Carboxylic Acids (R-COOH)
Acidic nature (react with bases to form salts).
Esterification (reaction with alcohols to form esters
- Esterification is the process of forming an ester from a carboxylic acid (RCOOH) and an alcohol (R'OH).
- The general equation for esterification is: RCOOH + R'OH ⇌ RCOOR' + H2O.
- An acid catalyst, such as concentrated sulfuric acid (H2SO4), is typically used to speed up the reaction.
- The acid-catalyzed esterification reaction is also known as Fischer esterification.
- The mechanism involves the protonation of the carbonyl oxygen in the carboxylic acid, followed by the nucleophilic attack of the alcohol on the carbonyl carbon, and then the elimination of water.
- Esters are compounds with the functional group R-COO-R', and they are often characterized by sweet or fruity smells.
- The esterification reaction is reversible, meaning that the ester can react with water to reform the carboxylic acid and alcohol.
- Ethanoic acid (CH3COOH) reacts with ethanol (C2H5OH) to form ethyl ethanoate (CH3COOC2H5) and water.
- Butanoic acid (CH3CH2CH2COOH) reacts with methanol (CH3OH) to form methyl butanoate (CH3CH2CH2COOCH3) and water.
- Ethanoic acid (CH3COOH) reacts with ethanol (C2H5OH) to form ethyl ethanoate (CH3COOC2H5) and water.
- Esters are used in various applications, including food flavorings, perfumes, and as solvents.
6. Important Polymers & Biomolecules
Polymers (Plastics, Rubber, Proteins, DNA)
Additional polymers: Polyethylene, PVC, Teflon.
Condensation polymers: Nylon, polyester.
Biomolecules
Carbohydrates (Sugars, starch, cellulose).
Proteins (Amino acids linked by peptide bonds).
Lipids (Fats, oils, steroids).
Nucleic Acids (DNA, RNA).
Conclusion:
This jog my basic memory about organic chemistry
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