The word 'organic' means pertaining to life. Originally, scientists believed organic compounds (like sugar, starch, proteins, and acetic acid) could only be produced by living organisms through a hypothetical 'Vital Force'.
Overthrow of Vital Force Theory:
Modern Definition: Organic chemistry is the study of carbon compounds (excluding oxides of carbon, carbonates, hydrogen carbonates, metal cyanides, and metal carbides).
| Characteristic | Organic Compounds | Inorganic Compounds |
|---|---|---|
| 1. Presence of Carbon | Carbon is an essential constituent element in every organic compound. | Carbon is not an essential element (except in carbonates/oxides). |
| 2. Water Solubility | Generally insoluble in water (except lower alcohols/acids). | Generally soluble in water. |
| 3. Organic Solvents | Soluble in organic solvents (alcohol, ether, benzene, chloroform). | Insoluble in organic solvents. |
| 4. Melting & Boiling Points | Low m.p. and b.p.; easily decompose on heating. | High m.p. and b.p.; generally heat stable. |
| 5. Combustibility | Inflammable; catch fire easily to form $CO_2$ and $H_2O$. | Non-inflammable; do not burn easily. |
| 6. Chemical Bonding | Form covalent bonds by sharing electrons. | Mostly form electrovalent (ionic) bonds. |
| 7. Electrical Conductivity | Non-electrolytes (do not conduct electricity). | Good electrolytes in aqueous or molten state. |
| 8. Isomerism | Exhibit the unique phenomenon of isomerism. | Isomerism is extremely rare or non-existent. |
| 9. Color & Smell | Possess characteristic colors and odours (e.g. fruity esters). | Mostly odorless and colorless. |
| 10. Reaction Speed | Molecular reactions are slow and reversible. | Ionic reactions are instantaneous and fast. |
Carbon forms more than 5 million known organic compounds due to two unique structural properties:
1. Tetravalency of Carbon:
Carbon (Atomic number = 6; Electronic configuration = 2, 4) has 4 valence electrons. To attain an octet, carbon shares 4 electrons with other atoms, forming four covalent bonds.
2. Catenation:
Catenation: The unique property of self-linking of atoms of an element through covalent bonds to form straight chains, branched chains, and cyclic (ring) structures of different sizes.
Reasons for Maximum Catenation in Carbon:
Hydrocarbons: Organic compounds composed exclusively of Carbon and Hydrogen atoms.
| Hydrocarbon Class | General Formula | Bonding Type | Examples |
|---|---|---|---|
| Alkanes (Paraffins) | $C_n H_{2n+2}$ | Single covalent bonds ($C-C$) | Methane ($CH_4$), Ethane ($C_2H_6$), Propane ($C_3H_8$) |
| Alkenes (Olefins) | $C_n H_{2n}$ | At least one double bond ($C=C$) | Ethene ($C_2H_4$), Propene ($C_3H_6$) |
| Alkynes (Acetylenes) | $C_n H_{2n-2}$ | At least one triple bond ($C\equiv C$) | Ethyne ($C_2H_2$), Propyne ($C_3H_4$) |
| Alicyclic (Cycloalkanes) | $C_n H_{2n}$ | Single bonds in closed ring | Cyclopropane ($C_3H_6$), Cyclohexane ($C_6H_{12}$) |
| Aromatic Hydrocarbons | Ring containing $C_6$ ring | Alternate single and double bonds | Benzene ($C_6H_6$), Toluene ($C_7H_8$), Phenol ($C_6H_5OH$) |
| Feature | Saturated Hydrocarbons (Alkanes) | Unsaturated Hydrocarbons (Alkenes & Alkynes) |
|---|---|---|
| Valency Satisfaction | All 4 valencies of carbon are satisfied by single covalent bonds. | Valencies are satisfied by double ($C=C$) or triple ($C\equiv C$) bonds. |
| Reactivity | Relatively unreactive (paraffins); undergo substitution reactions. | Highly reactive due to multiple bonds; undergo addition reactions. |
| Flame Type | Burn with a clean, non-sooty blue flame. | Burn with a yellow, luminous, sooty flame due to higher $\% C$. |
| Bromine Water Test | Do not decolourise orange bromine water. | Decolourise orange bromine water to colorless solution. |
Alkyl Radical / Group: A univalent group obtained by removing one hydrogen atom from an alkane molecule.
$$\text{Alkane } (C_n H_{2n+2}) \xrightarrow{-H} \text{Alkyl Group } (C_n H_{2n+1})$$| Parent Alkane | Formula | Alkyl Group | Formula | Abbreviated Structure |
|---|---|---|---|---|
| Methane | $CH_4$ | Methyl | $-CH_3$ | CH3− |
| Ethane | $C_2H_6$ | Ethyl | $-C_2H_5$ | CH3−CH2− |
| Propane | $C_3H_8$ | Propyl | $-C_3H_7$ | CH3−CH2−CH2− |
| Butane | $C_4H_{10}$ | Butyl | $-C_4H_9$ | CH3−(CH2)2−CH2− |
ICSE Board mandates structural formulas for Alkanes, Alkenes, and Alkynes up to 5 carbon atoms ($C_1$ to $C_5$):
| Class | IUPAC Name | Molecular Formula | Condensed Formula | Full Structural Formula |
|---|---|---|---|---|
| Alkanes ($C_n H_{2n+2}$) | Methane | $CH_4$ | $CH_4$ | H−C(H2)−H (1 Carbon, 4 H) |
| Ethane | $C_2H_6$ | CH3−CH3 | H3C−CH3 | |
| Propane | $C_3H_8$ | CH3−CH2−CH3 | H3C−CH2−CH3 | |
| Butane | $C_4H_{10}$ | CH3−(CH2)2−CH3 | H3C−(CH2)2−CH3 | |
| Pentane | $C_5H_{12}$ | CH3−(CH2)3−CH3 | H3C−(CH2)3−CH3 | |
| Alkenes ($C_n H_{2n}$) | Ethene | $C_2H_4$ | CH2=CH2 | H2C=CH2 |
| Propene | $C_3H_6$ | CH3−CH=CH2 | H3C−CH=CH2 | |
| But-1-ene | $C_4H_8$ | CH3−CH2−CH=CH2 | H3C−CH2−CH=CH2 | |
| Pent-1-ene | $C_5H_{10}$ | CH3−(CH2)2−CH=CH2 | H3C−CH2−CH2−CH=CH2 | |
| Alkynes ($C_n H_{2n-2}$) | Ethyne | $C_2H_2$ | HC≡CH | H−C≡C−H |
| Propyne | $C_3H_4$ | CH3−C≡CH | H3C−C≡CH | |
| But-1-yne | $C_4H_6$ | CH3−CH2−C≡CH | H3C−CH2−C≡CH | |
| Pent-1-yne | $C_5H_8$ | CH3−(CH2)2−C≡CH | H3C−CH2−CH2−C≡CH |
Homologous Series: A group of organic compounds having similar structure, similar chemical properties, and the same functional group, in which successive members differ from each other by a $-CH_2-$ group (methylene group) and by a molecular mass of $14 \text{ amu}$.
5 KEY CHARACTERISTICS OF A HOMOLOGOUS SERIES:
Definition: An atom or a group of atoms attached to a carbon chain that defines the structure and determines the characteristic chemical properties of an organic compound.
| Functional Group | Structure | Class | IUPAC Suffix/Prefix | Example (IUPAC) |
|---|---|---|---|---|
| Halide | $-X \text{ (F, Cl, Br, I)}$ | Haloalkanes | Prefix: Halo- | $CH_3Cl$ (Chloromethane) |
| Hydroxyl | $-OH$ | Alcohols | Suffix: -ol | $C_2H_5OH$ (Ethanol) |
| Aldehyde | $-CHO$ ($-C(=O)H$) | Aldehydes | Suffix: -al | $CH_3CHO$ (Ethanal) |
| Carboxyl | $-COOH$ ($-C(=O)OH$) | Carboxylic Acids | Suffix: -oic acid | $CH_3COOH$ (Ethanoic acid) |
| Keto (Carbonyl) | $>C=O$ | Ketones | Suffix: -one | $CH_3COCH_3$ (Propan-2-one) |
| Ether | $-O-$ | Ethers | Prefix: Alkoxy- | $CH_3-O-CH_3$ (Methoxy methane) |
| Ester | $-COOR$ | Esters | Suffix: -oate | $CH_3COOC_2H_5$ (Ethyl ethanoate) |
Isomerism: Compounds having the same molecular formula but different structural formulas (and different physical/chemical properties) are called isomers, and the phenomenon is known as isomerism.
1. Chain Isomerism: Occurs when two or more compounds have the same molecular formula but differ in the arrangement of carbon skeleton (straight vs branched chain).
• Isomers of Butane ($C_4H_{10}$):
• Isomers of Pentane ($C_5H_{12}$):
2. Position Isomerism: Occurs when two or more compounds have the same molecular formula and carbon skeleton but differ in the position of substituent atom, double/triple bond, or functional group.
3. Functional Group Isomerism: Same molecular formula but different functional groups.
IUPAC (International Union of Pure and Applied Chemistry) system assigns systematic names consisting of 3 parts:
| Carbon Count | Root Word | Carbon Count | Root Word |
|---|---|---|---|
| $C_1$ | Meth- | $C_6$ | Hex- |
| $C_2$ | Eth- | $C_7$ | Hept- |
| $C_3$ | Prop- | $C_8$ | Oct- |
| $C_4$ | But- | $C_9$ | Non- |
| $C_5$ | Pent- | $C_{10}$ | Dec- |
MASTER IUPAC NAMING RULES:
| Trivial (Common) Name | IUPAC Name | Formula | Class of Compound |
|---|---|---|---|
| Marsh Gas / Fire-damp | Methane | $CH_4$ | Alkane |
| Ethylene | Ethene | $C_2H_4$ | Alkene |
| Acetylene | Ethyne | $C_2H_2$ | Alkyne |
| Methyl iodide | Iodomethane | $CH_3I$ | Haloalkane |
| Ethyl bromide | Bromoethane | $C_2H_5Br$ | Haloalkane |
| Chloroform | Trichloromethane | $CHCl_3$ | Haloalkane |
| Formaldehyde | Methanal | $HCHO$ | Aldehyde |
| Acetaldehyde | Ethanal | $CH_3CHO$ | Aldehyde |
| Acetone | Propan-2-one | $CH_3COCH_3$ | Ketone |
| Formic Acid | Methanoic Acid | $HCOOH$ | Carboxylic Acid |
| Acetic Acid / Vinegar | Ethanoic Acid | $CH_3COOH$ | Carboxylic Acid |
Methane is the simplest saturated hydrocarbon. It occurs in marshy areas (called marsh gas) due to anaerobic bacterial decomposition of cellulose, in coal mines (called fire-damp), and is a primary greenhouse gas.
1. Laboratory Preparation of Methane ($CH_4$):
• Reactants: Sodium Ethanoate (Sodium Acetate, $CH_3COONa$) + Soda Lime ($NaOH + CaO$).
• Role of $CaO$ in Soda Lime: $NaOH$ is deliquescent and attacks glass. $CaO$ makes soda lime porous, dry, and prevents glass cracking!
• Reaction (Decarboxylation):
$$\text{CH}_3\text{COONa} + \text{NaOH} \xrightarrow{\text{CaO}, 300^\circ\text{C}} \text{Na}_2\text{CO}_3 + \text{CH}_4\uparrow$$• Collection: Over water by downward displacement of water (since methane is insoluble in water and lighter than air).
2. Laboratory Preparation of Ethane ($C_2H_6$):
• From Sodium Propanoate (Sodium Propionate):
$$\text{C}_2\text{H}_5\text{COONa} + \text{NaOH} \xrightarrow{\text{CaO}, 300^\circ\text{C}} \text{Na}_2\text{CO}_3 + \text{C}_2\text{H}_6\uparrow$$3. Preparation from Alkyl Halides (Reduction):
• From Iodomethane (Methyl Iodide): $CH_3I + 2[H] \xrightarrow{Zn/HCl} CH_4 + HI$
• From Bromoethane (Ethyl Bromide): $C_2H_5Br + 2[H] \xrightarrow{Zn/Cu \text{ couple in alcohol}} C_2H_6 + HBr$
4. Other Methods of Preparation:
• Action of Water on Aluminium Carbide: $Al_4C_3 + 12H_2O \rightarrow 3CH_4\uparrow + 4Al(OH)_3\downarrow$
• Wurtz Reaction (for Ethane):
$$2\text{CH}_3\text{I} + 2\text{Na} \xrightarrow{\text{dry ether}} \text{CH}_3-\text{CH}_3 + 2\text{NaI}$$1. Complete vs Incomplete Combustion (ICSE EXAM MANDATE):
2. Substitution Reaction with Chlorine (in Diffused Sunlight):
• Methane Step-by-Step Chlorination:
$$\text{CH}_4 + \text{Cl}_2 \xrightarrow{h\nu} \text{CH}_3\text{Cl} + \text{HCl}$$(Step 1: Chloromethane)
$$\text{CH}_3\text{Cl} + \text{Cl}_2 \xrightarrow{h\nu} \text{CH}_2\text{Cl}_2 + \text{HCl}$$(Step 2: Dichloromethane)
$$\text{CH}_2\text{Cl}_2 + \text{Cl}_2 \xrightarrow{h\nu} \text{CHCl}_3 + \text{HCl}$$(Step 3: Trichloromethane / Chloroform)
$$\text{CHCl}_3 + \text{Cl}_2 \xrightarrow{h\nu} \text{CCl}_4 + \text{HCl}$$(Step 4: Tetrachloromethane / Carbon Tetrachloride)
• Ethane Step-by-Step Chlorination:
$$\text{C}_2\text{H}_6 + \text{Cl}_2 \xrightarrow{h\nu} \text{C}_2\text{H}_5\text{Cl} + \text{HCl}$$(Step 1: Chloroethane)
$$\text{C}_2\text{H}_5\text{Cl} \xrightarrow{+5\text{Cl}_2, h\nu} \text{C}_2\text{Cl}_6 + 5\text{HCl}$$(Final Step: Hexachloroethane)
3. Catalytic Controlled Oxidation of Methane:
(Product: Methanol / Methyl Alcohol)
(Product: Methanal / Formaldehyde)
(Product: Methanoic Acid / Formic Acid)
4. Pyrolysis / Cracking:
$$\text{CH}_4 \xrightarrow{1500^\circ\text{C}} \text{HC}\equiv\text{CH} + 3\text{H}_2\uparrow$$(Methane converted to Ethyne gas)
Ethene (Ethylene) is the first member of the alkene series ($C_n H_{2n}$). It is an unsaturated hydrocarbon containing a double covalent bond ($C=C$). Structure is planar with $120^\circ$ bond angles.
1. Dehydration of Ethanol (Lab Method):
$$\text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{conc. } \text{H}_2\text{SO}_4, 170^\circ\text{C}} \text{CH}_2=\text{CH}_2\uparrow + \text{H}_2\text{O}$$• Purification: Passed through $NaOH$ solution to remove $SO_2$ and $CO_2$ formed by partial reduction of $H_2SO_4$.
• Industrial Dehydration: Ethanol vapour passed over heated Alumina at $350^\circ C$ ($C_2H_5OH \xrightarrow{Al_2O_3, 350^\circ C} C_2H_4 + H_2O$).
2. Dehydrohalogenation of Bromoethane:
$$\text{C}_2\text{H}_5\text{Br} + \text{alcoholic KOH} \xrightarrow{\text{boil}} \text{CH}_2=\text{CH}_2\uparrow + \text{KBr} + \text{H}_2\text{O}$$1. Hydrogenation (Addition of Hydrogen):
$$\text{CH}_2=\text{CH}_2 + \text{H}_2 \xrightarrow{\text{Ni / Pt}, 200^\circ\text{C}} \text{CH}_3-\text{CH}_3 \quad (\text{Ethene } \rightarrow \text{ Ethane})$$2. Halogenation (Addition of $Cl_2, Br_2, I_2$):
(Orange-red Bromine solution decolourises to colorless 1,2-dibromoethane)
CRITICAL EXAM TEST: The decolourisation of reddish-orange Bromine solution in $CCl_4$ is the standard laboratory test for unsaturation (double or triple bond)!
3. Baeyer's Test (Oxidation with Cold Alkaline $KMnO_4$):
$$\text{CH}_2=\text{CH}_2 + \text{H}_2\text{O} + [\text{O}] \xrightarrow[\text{alk. } \text{KMnO}_4]{\text{cold}} \text{CH}_2\text{OH}-\text{CH}_2\text{OH}$$(Product: 1,2-Ethanediol / Ethylene Glycol)
The purple color of $KMnO_4$ fades and decolourises completely!
4. Polymerization:
$$n(\text{CH}_2=\text{CH}_2) \xrightarrow[\text{high } P, T]{\text{catalyst}} [-\text{CH}_2-\text{CH}_2-]_n$$(Ethene monomer $\rightarrow$ Polyethene / Polythene polymer)
Ethyne (Acetylene) is the first member of alkynes ($C_n H_{2n-2}$). Contains a triple covalent bond ($C\equiv C$). Molecule geometry is linear with $180^\circ$ bond angle.
1. From Calcium Carbide ($CaC_2$):
$$\text{CaC}_2 + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{HC}\equiv\text{CH}\uparrow \quad (\Delta H = \text{Exothermic})$$• Purification: Gas is passed through acidified Copper Sulphate ($CuSO_4$) solution to absorb impurities like Phosphine ($PH_3$), Hydrogen Sulphide ($H_2S$), and Ammonia ($NH_3$).
• Collection: Over water by downward displacement of water.
2. From 1,2-dibromoethane:
$$\text{CH}_2\text{Br}-\text{CH}_2\text{Br} + 2\text{alc. KOH} \xrightarrow{200^\circ\text{C}} \text{HC}\equiv\text{CH}\uparrow + 2\text{KBr} + 2\text{H}_2\text{O}$$| Reagent / Test | Alkane (Ethane) | Alkene (Ethene) | Alkyne (Ethyne) |
|---|---|---|---|
| 1. Bromine in $CCl_4$ | No change (orange color stays). | Orange color decolourises. | Orange color decolourises. |
| 2. Alkaline $KMnO_4$ (Baeyer's) | No change (purple color stays). | Purple color decolourises. | Purple color decolourises. |
| 3. Ammoniacal $Cu_2Cl_2$ Solution | No observation. | No observation. | Red Precipitate of Copper Acetylide ($Cu_2C_2\downarrow$). |
| 4. Ammoniacal $AgNO_3$ Solution | No observation. | No observation. | White Precipitate of Silver Acetylide ($Ag_2C_2\downarrow$). |
Ethanol (Ethyl alcohol, $C_2H_5OH$) is a hydroxyl derivative of ethane. It is known as grain alcohol or spirit of wine.
1. Lab Preparation (Hydrolysis of Bromoethane):
$$\text{C}_2\text{H}_5\text{Br} + \text{aq. KOH} \xrightarrow{\text{boil}} \text{C}_2\text{H}_5\text{OH} + \text{KBr}$$2. Industrial Fermentation of Sugar / Molasses:
$$\text{C}_{12}\text{H}_{22}\text{O}_{11} + \text{H}_2\text{O} \xrightarrow{\text{Invertase (Yeast)}} \text{C}_6\text{H}_{12}\text{O}_6 \text{ (Glucose)} + \text{C}_6\text{H}_{12}\text{O}_6 \text{ (Fructose)}$$ $$\text{C}_6\text{H}_{12}\text{O}_6 \xrightarrow{\text{Zymase (Yeast)}} 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2\uparrow$$PHYSICAL PROPERTIES OF ETHANOL (ICSE SYLLABUS MANDATE):
1. Action with Sodium Metal (Effervescence Test):
$$2\text{C}_2\text{H}_5\text{OH} + 2\text{Na} \rightarrow 2\text{C}_2\text{H}_5\text{ONa} + \text{H}_2\uparrow$$(Sodium ethoxide formed with brisk effervescence of $H_2$ gas)
2. Oxidation with Acidified $K_2Cr_2O_7$:
$$\text{C}_2\text{H}_5\text{OH} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7 / \text{H}^+]{[\text{O}]} \text{CH}_3\text{CHO} \xrightarrow{[\text{O}]} \text{CH}_3\text{COOH}$$(Ethanol $\rightarrow$ Ethanal $\rightarrow$ Ethanoic acid)
Orange color of Potassium dichromate turns Green due to formation of $Cr^{3+}$ ions!
3. Esterification (Fruity Smell Test):
$$\text{C}_2\text{H}_5\text{OH} + \text{CH}_3\text{COOH} \xrightarrow{\text{conc. } \text{H}_2\text{SO}_4, \Delta} \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O}$$(Product: Ethyl acetate with pleasant fruity smell)
4. Dehydration Reactions:
Ethanoic acid (Acetic acid) is a monocarboxylic acid containing $-COOH$ functional group. Structure: $CH_3-C(=O)-OH$.
PHYSICAL PROPERTIES OF ACETIC ACID (ICSE SYLLABUS MANDATE):
1. Lab Preparation (Oxidation of Ethanol):
$$\text{CH}_3\text{CH}_2\text{OH} + 2[\text{O}] \xrightarrow{\text{K}_2\text{Cr}_2\text{O}_7 / \text{H}_2\text{SO}_4} \text{CH}_3\text{COOH} + \text{H}_2\text{O}$$2. Industrial Manufacture from Acetylene:
$$\text{HC}\equiv\text{CH} + \text{H}_2\text{O} \xrightarrow{40\% \text{H}_2\text{SO}_4, 1\% \text{HgSO}_4, 60^\circ\text{C}} \text{CH}_3\text{CHO} \xrightarrow{\text{O}_2, \text{Mn(CH}_3\text{COO)}_2} 2\text{CH}_3\text{COOH}$$1. Acidic Nature & Litmus Test: Turns blue litmus red. Weak monobasic acid ($CH_3COOH \rightleftharpoons CH_3COO^- + H^+$).
2. Reaction with Alkalis (Neutralization):
$$\text{CH}_3\text{COOH} + \text{NaOH} \rightarrow \text{CH}_3\text{COONa } (\text{Sodium acetate}) + \text{H}_2\text{O}$$3. Reaction with Carbonates & Bicarbonates (Brisk Effervescence):
$$2\text{CH}_3\text{COOH} + \text{Na}_2\text{CO}_3 \rightarrow 2\text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2\uparrow$$ $$\text{CH}_3\text{COOH} + \text{NaHCO}_3 \rightarrow \text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2\uparrow$$4. Reaction with Active Metals:
$$2\text{CH}_3\text{COOH} + \text{Zn} \rightarrow (\text{CH}_3\text{COO})_2\text{Zn } (\text{Zinc acetate}) + \text{H}_2\uparrow$$5. Neutral $FeCl_3$ Test for Acetic Acid:
On adding neutral Ferric Chloride solution to acetic acid, a wine-red color solution is produced!
| Compound | Official ICSE Board Exam Uses |
|---|---|
| Methane ($CH_4$) | 1. Fuel in household CNG gas. 2. Manufacturing Carbon Black for printing ink & automobile tires. 3. Synthesis of Chloroform, Formaldehyde, and Methyl Alcohol. |
| Ethane ($C_2H_6$) | 1. Fuel in gaseous fuel mixtures. 2. Industrial preparation of Ethene by dehydrogenation. 3. Preparation of chloro-derivatives. |
| Ethene ($C_2H_4$) | 1. Artificial ripening of green fruits. 2. Oxy-ethylene flame for welding and cutting metals. 3. Manufacture of Polyethene plastic and Ethylene Glycol antifreeze. |
| Ethyne ($C_2H_2$) | 1. Oxy-acetylene flame ($3000^\circ C$) for welding & cutting metals. 2. Artificial ripening of fruits. 3. Manufacture of synthetic rubber (Neoprene), Westron & Westrosol solvents. |
| Ethanol ($C_2H_5OH$) | 1. Solvent for paints, varnishes, dyes, and Tincture of Iodine. 2. Fuel in motor cars (Power Alcohol = 20% ethanol + 80% petrol). 3. Manufacturing alcoholic beverages, perfumes, and chloroform. |
| Ethanoic Acid ($CH_3COOH$) | 1. Food preservative & flavoring agent as Vinegar ($4-5\%$ aqueous acetic acid). 2. Coagulation of rubber latex. 3. Manufacture of Cellulose Acetate rayon film, dyes, and esters. |
