JEE Organic Chemistry Final Notes PDF

Welcome to Organic Chemistry: Some Basic Principles and Techniques Wohler Theory Organic Compounds Tetravalency of Carbon and Catenation Tendency to form Bonds with other Non-metals Bonding in Organic Compounds 𝛔 𝛑 Representation of Organic Molecules Structural Representation: Complete/Expanded Form...

Welcome to Organic Chemistry: Some Basic Principles and Techniques Wohler Theory Organic Compounds Tetravalency of Carbon and Catenation Tendency to form Bonds with other Non-metals Bonding in Organic Compounds 𝛔 𝛑 Representation of Organic Molecules Structural Representation: Complete/Expanded Formula Condensed Formula Bond Line Formula 3D Representation of Organic Molecules Classification of Organic Compounds Classification of Organic Compounds Classification of Organic Compounds Classification of Organic Compounds Classification of Organic Compounds.. Hydrocarbons Saturated and Unsaturated Hydrocarbons ≡ Functional Group Naming IUPAC IUPAC Nomenclature Word Root Meth Hept Prop Non But Dec Pent Undec Hex Dodec Primary Suffix Naming Saturated Hydrocarbons Primary Prefix Straight Chain Hydrocarbon Cyclic and Branched Hydrocarbon Alkyl Groups Straight Chain Alkyl Groups Some Important Alkyl Groups Some Important Alkyl Groups Nomenclature of Saturated Hydrocarbons (Alkanes) Determining the Parent Chain Chains with Equal Length Chains with Equal Number of Substituents Assigning Locants Numbering of Carbon Chain The number that indicates the position of the substituent, side chain, multiple bonds or functional group. Numbering in the Presence of Multiple Substituents This is the first point of difference as from both the direction, the numbering starts with same number (2) Substituents in Alphabetical Order The chain numbered from left to right is preferred because the substituent “ethyl” comes at C-3 while from right to left, at C3, “methyl” substituent comes first. As ‘e’ comes before ‘m’, lowest number with “ethyl” substituent is correct. In the IUPAC Name of a Compound Secondary Prefix Substituents in Alphabetical Order Substituents in Alphabetical Order Occurrence of a Substituent More Than Once Occurrence of a Substituent More Than Once Complex Substituents Complex Substituents Deciding the Alphabetical Order Deciding the Alphabetical Order Presence of Similar Complex Substituents Deciding the Alphabetical Order Point to Remember!! Nomenclature of Unsaturated Hydrocarbons Parent Chain Selection Assigning Locants IUPAC Nomenclature of Polyenes/Poly-ynes Point to Remember!! Alkene/Alkyne as Substituent Groups −Alkane Alkyl −Alkene Alkeny −Alkyne Alkyny Examples Alkene/Alkyne as Substituent Groups Nomenclature of Cyclic Hydrocarbons Parent Chain Selection Rule for Selection of Parent Chain: Maximum number of multiple bonds > Maximum number of carbon All are same > Cyclic part Parent chain Maximum number of substituents Remember!! Assigning Locants Nomenclature of Organic Compounds with Functional Groups Nomenclature Secondary Prefix Substituent group Secondary prefix ─R Alkyl ─X Halo ─ NO2 Nitro ─ OR Alkoxy ─ NO Nitroso Carboxylic Acids Sulphonic Acids O H3C S O OH Acid Anhydride Esters Acid Halides Amides Amides Cyanide ≡ Isocyanide ≡ Cyanide and isocyanide are two different functional group. Also, cyanide has more priority over isocyanide. Aldehydes and Ketones Alcohols and Thiols Amines Amines IUPAC Nomenclature of Compounds Containing Functional Groups Parent Chain Selection Assigning Locants Assigning Locants O CH3 CH2 CH COOH CH3 CH3 C C CH2 C H Point to Remember!! Examples Naming Compounds Containing Functional Groups C O CH 2 C O CH3 CH3 Naming Compounds Containing Functional Groups Principal Functional Group Some Important Points Some Important Points Some Important Points Some Important Points Some Important Points Point to Remember!! Functional Group Suffix –CHO Carbaldehyde –COOH Carboxylic Acid –COX Carbonyl halide –COOR Alkyl Carboxylate –CONH2 Carboxamide –CN Carbonitrile Example Point to Remember!! HOOC COOH COOH Nomenclature of Aromatic Compounds Aromatic Compounds Examples F Cl Br NO2 Nomenclature of Benzene Derivatives Nomenclature of Benzene Derivatives Nomenclature of Benzene Derivatives New Base Name New Base Name Naming with New Base Name Nomenclature of Benzene Derivatives CH2 CH Nomenclature of Benzene Derivatives Benzene as Substituent H3C CH CH3 OH O Isomerism Isomerism The phenomenon of existence of two or more compounds possessing the same molecular formula but different properties is known as isomerism. Such compounds are known as isomers. Classification of Isomers Structural isomers (Constitutional) Isomers Stereoisomers (Space/ 3D) Structural Isomers Compounds having the same molecular formula but different structural formula i.e., they differ in the bonding sequence of their atoms. Structural Isomers Example: Straight chain n-hexane and branched chain 2-methylpentane are the structural isomers of C6H14. n-hexane 2-Methylpentane Structural isomers in C6H14 Stereo Isomers Isomers that have the same bonding sequence of atoms & groups but differ from each other only in the way their atoms are oriented in space Stereo Isomers Example: cis-2-Butene trans-2-Butene Stereoisomers in But-2-ene Structural Isomers Chain Isomers Example Example Example Position Isomers Example Example Example Example Functional Isomers Examples Examples Examples Examples Examples Examples Ring-Chain Isomers One isomer has a ring & the other has an aliphatic chain. Ring-Chain isomers are also functional isomers. Example Propene C3H6 Cyclopropane Example Hexene C6H12 Cyclohexane H2 C Metamers O O R’ R O O O C O O Metamers N N NH H C O N C O S Metamers Metamers N H N H Metamers Tautomerism Tautomerism Diad Tautomerism Triad Diad Tautomerism ↔ ⇌ Diad Tautomerism Triad Tautomerism ↔ ⇌ Conditions for Tautomerism O N O O NH N O Conditions for Tautomerism ⍺ ⇌ Conditions for Tautomerism ⍺ ꞵ ⇌ 𝛄 𝝱 𝛄 ⇌ Keto-Enol Tautomerism ⍺ ⇌ Keto-Enol Tautomerism ↽ ⇀ Keto-Enol Tautomerism ∼ ∼ Examples ↽ ⇀ ↽ ⇀ ∼ Keto-Enol Tautomerism ↽ ⇀ Keto-Enol Tautomerism However, in certain cases, the % enol content predominates the % keto content! ∝ ∝ ∝ Keto-Enol Tautomerism 𝝱 % Enol ⇌ 𝛄 ∝ 1 Polarity of solvent Keto-Enol Tautomerism ↽ ⇀ Keto-Enol Tautomerism ⇀ ↽ Keto-Enol Tautomerism O HO O ⇀ ⇀ O Keto-Enol Tautomerism ⇀ ⇀ ∼ Keto-Enol Tautomerism Percentage of enol increases with the stability of Alkene CH3 CHO ⇌ H3C CH2 CHO H3C CH CHO CH3 H2C ⇌ CH HC H3C ⇌ OH H3C CH C CH3 CH OH OH Keto-Enol Tautomerism 𝛽 𝛂 Follow RTFMCP!! Degree of Unsaturation 𝛑 Degree of Unsaturation − Degree of Unsaturation 𝛑 𝛑 𝛑 Remember!!! C C OH C C OH C OH OH Remember!!! C OR OH C OH O C C C C NH2 Classification of Isomers Isomers Structural (Constitutional) Stereoisomers (Space/3D) Configurational Conformational Configurational Isomers H3C CH3 C H H C CH3 C H H3C C H Conformational Isomers 𝛔 𝛔 𝛔 Conformational Isomers Quick Contrast Conformational Isomers Configurational The dog in the right has tail in place of leg and leg in place of tail Configurational isomers are different compounds (for example, cis and trans isomers). They can be separated from each other. Bonds have to be broken to interconvert compounds with different configuration. Conformational The left one is in stable position while the right one is in unstable position Conformers are different spatial arrangements of the same compound. They cannot be separated. Some conformers are more stable than others Projection Formulae A projection formula indicates spatial arrangement of bonds. Sawhorse Projection Newman Projection Interconversion between Projections Dihedral Angle (Φ) Φ Φ Conformational Isomers Eclipsed Conformation Eclipsed Conformation of Ethane Staggered Conformation Staggered Conformation of Ethane Skew Conformation Skew Conformation of Ethane Factors Affecting Stability of Conformations Angle Strain Torsional Strain Van der Waals Strain Conformational Energy Conformational Energy Conformations in Open-Chain Systems Conformers of Ethane Conformers of Ethane Conformational Analysis of Ethane Stability of Eclipsed v/s Staggered form Conformational Analysis of Ethane Conformations v/s Conformers Conformers of Propane * * * * Conformers of Propane * H H * CH3 H * H H * Conformational Analysis of Propane Stability of Eclipsed v/s Staggered form ϕ ϕ Conformers of Butane ϕ ϕ ϕ ϕ ϕ ϕ Conformation of Butane Dihedral angle (Ф) Torsional strain van der Waals strain Stability Anti 180° Absent Absent Maximum Maximum Present (Between -CH3 & -H groups) Intermediate-1 Partially Eclipsed 120°/ 240° Conformation of Butane Gauche Fully eclipsed Dihedral angle (Ф) 60°/300° 0° Torsional strain van der Waals strain Stability Absent Present (between two -CH3 groups) Intermediate-2 (> Intermediate-1) Maximum Maximum (between two -CH3 groups) Minimum Stability of Conformations of Butane > ϕ = 180o > ϕ = 60o ≡ > ϕ = 120o ≡ ϕ = 0o Fully Eclipsed Anti (Staggered) ϕ = 300o ϕ = 240o Gauche (Staggered) Partially Eclipsed Conformations v/s Conformers Butane can exist in an infinite number of conformations, but it has only 3 conformers (two gauche and one anti). Intramolecular Hydrogen Bonding Order of Stability F H H F H O H > H H H H H OH Dipole Moment For conformational isomers, μobserved = Σμi 𝜒i ⇒ = μobserved 𝜒gauche ＋ 𝜒anti = μ = Dipole moment 𝜒 = Mole fraction μgauche 𝜒gauche ＋ μanti 𝜒anti 1 Conformations of Cyclohexane Cycloalkanes Cycloalkanes do not have the same relative stability Cyclohexane is stable in comparison to cyclopropane, cyclobutane and cyclopentane Difference in relative stabilities is due to angle & torsional strain. Conformations of Cyclohexane Half Chair form Boat form Twist boat form Chair form Chair Conformation of Cyclohexane Drawing Carbon Skeleton of Chair Form I II III IV Adding Hydrogen Atoms Adding axial H atoms Adding equatorial H atoms Conformations of Cyclohexane Flagpole interaction H Chair Conformation of Cyclohexane H Boat Conformation of Cyclohexane Conformations of Cyclohexane Stability Order H H3C N CH3 O C6 H 5 CH3 H3C CH3 In some molecules, due to intramolecular hydrogen bonding stabilization exist in boat form rather than in chair form. Ring Flipping of Cyclohexane ⇌ ⇌ ⇌ ⇌ ⇌ Energy Profile Diagram (3D) Conformations of Substituted Cyclohexane Conformations of Monosubstituted Cyclohexane Two different chair conformations: One with the substituent at axial position & the other with the substituent at equatorial position X ↽ ⇀ X Conformations of Monosubstituted Cyclohexane In almost all cases, the conformation with the substituent at axial position is higher in energy than the one with the substituent at equatorial position. Conformations of Monosubstituted Cyclohexane Methyl substituent is equatorial Methyl substituent is axial More Stable Less Stable 1,3-Diaxial Interaction Interaction between an axial group on carbon atom ‘1’ and an axial hydrogen on carbon atom ‘3’ (or 5). 1,3-Diaxial Interaction 1,3-diaxial interaction Conformations of Poly-substituted Cyclohexane Conformations of Polysubstituted Cyclohexane Conformations of Polysubstituted Cyclohexane General Organic Chemistry Bond Cleavage Bond Cleavage Homolytic Cleavage Heterolytic Cleavage Intermediates Intermediates + Carbocation (CH3 ) Free radical (CH3 ) Carbanion (CH3 ) Electron Displacement Effect Permanent Effect 𝛅 𝛅 The fractional electronic charges on the two atoms in a polar covalent bond are called partial charges and are denoted by ẟ+/ẟ- Temporary Effect CH2 CH2 E⊕ CH2 CH2 E I Inductive Effect 𝞂 Characteristics of Inductive Effect 𝛔 𝛑 𝛅𝛅𝛅+ C C 𝛅𝛅+ 𝛅+ 𝛅- > C >> C >>> Cl Inductive Effect I I 0 H -100 -2 -1 0 +1 +2 +I strength NF3 F NH2 H CH3 CR3 +I Effect Order of +I Order of +I Order of +I −I Effect Order of −I I ≡ Order of −I Order of −I I Direction of Electron Displacements CH3 > > C > > CH2 > CH2 CH3 CH3 H3C OOC CH3 > HOOC CH3 > + 𝛅+ CH2 > CH3 > C 𝛅𝛅- 𝛅- _ 𝛅𝛅+ CH3 CH3 Applications of Inductive Effect Intermediates − ∝ I ∝ I Acid Dissociation Constant for HA ⇌ ∝ I ∝ ∝ I For a Base ‘B’ ⇌ ∝ I ∝ ∝ I ∝ I ∝ I ∝ Resonance Resonance Resonance and Resonating structures Resonating Structures (R.S.) Resonance Hybrid Resonance 𝛑 𝛑 Conjugation Types of Conjugation Types of Conjugation Types of Conjugation 𝛑 Types of Conjugation 𝛑 H H + NH2 NH2 H NH2 Types of Conjugation Extended Conjugation Extended Conjugation Cross Conjugation Cross Conjugation Remember!!! To have resonance, the porbitals should be in a plane but here the p-orbitals involved in π bonding are perpendicular to each other. Drawing Resonating Structures O Drawing Resonating Structures 𝛑 Rules for Resonating Structures _ H C + OH H CH3 + CH CH CH2 CH3 CH CH + CH2 + CH2 CH2 CH CH2 Rules for Resonating Structures Rules for Resonating Structures Resonating Structures of Phenoxide ion Point to Remember!! Point to Remember!! + + Point to Remember!! – - Point to Remember!! H Point to Remember!! H + N H H N+ Point to Remember!! H + O H O + Resonating Structures Equivalent Contributing Resonating Structures Resonance Comparing the Stabilities of the Resonating Structures Comparing the Stabilities of the Resonating Structures Comparing the Stabilities of the Resonating Structures Comparing the Stabilities of the Resonating Structures _ S S O R R _ Comparing the Stabilities of the Resonating Structures Point to Remember!! Resonance Energy ∝ Mesomeric Effect 𝛑 Types of Mesomeric Effects +M Effect H H2C C H O CH3 – H2C C + O CH3 Example Positive Mesomeric effect (+M effect) I NH 2 NH NH 2 2 NH NH 2 2 Negative Mesomeric effect (-M effect) When the group withdraws electrons from the conjugated system, it shows - M effect. ≡ −M Effect O N Negative Mesomeric effect (-M effect) N O O O O + N + O O N + + N O + + O + + N O O Flexible Groups Brace Yourself! Steric Inhibition of Resonance (SIR) Effect Example NH2 H3C N CH3 CH3 H3C COOH COOH Cl CH3 H3 C H3C CH3 COOH Br N CH3 I Example H3C N CH3 H3C N CH3 CH3 H3C H3C N CH3 CH3 Applications of Resonance Effect Stability of Intermediates Bond Length Partial double bond character due to conjugation of pi bonds Example As nitro group shows more –M effect, so, more electron density is given by NH2 group to the ring resulting in more double bond character. N Acidic Strength OH OH O R OCH3 CH3 S O O O H C R OH Basic Strength NH2 NH2 NH2 O CH3 Hyperconjugation 𝛔 𝛑 𝞂 𝛑 𝛔 𝛑 Condition for Hyperconjugation 𝛂 𝛂−Carbon 𝛂 𝛂 𝛂−Hydrogen 𝛂 α 𝛂 Hyperconjugation Hyperconjugation in Ethyl Carbocation Hyperconjugation in Ethyl Carbocation Hyperconjugation in Ethyl Free Radical Bond Length ⍺ ⍺ ⍺ More the number of ⍺ , more the hyperconjugation and more involvement of double bond. Reverse Hyperconjugation (−H effect) Cl 𝛑 Cl Cl Cl C CH CH2 C Cl Cl CH2 Cl _ CH + CH2 CH + CH2 Cl C Cl CH Cl Cl Cl C Cl 𝛔 CH _ + CH2 Cl _ C Cl Example Cl Cl Cl C Cl Cl C Cl Cl- Cl C Cl- + Cl Cl + + C Cl- Cl Cl C Cl Electromeric Effect 𝛑 +E Effect and -E Effect 𝛑 𝛑 Aromaticity 𝛑 Aromatic Compounds 𝛑 Benzene as an Aromatic Compound 𝛑 𝛑 Benzenoid Polycyclic Aromatic Hydrocarbons Anti-Aromatic Compounds 𝛑 Cyclobutadiene as an Anti-Aromatic Compound 𝛑 𝛑 Non-Aromatic Compounds Annulene Quasi-Aromatic Quasi-Aromatic Which one is more stable? > > Heterocyclic Aromatic Compound Peripheral Conjugation Benzyne and Azulene Applications of Electronic Effects Stability of Reaction Intermediates Carbocation Carbocation (CH3+) Stability of Carbocation I Stability Order + + CH2 CH CH Ph Ph2CH Ph3C + + + + CH CH3 CH3 CH 3 C + CH 3 Ph CH3 + CH2 Stability Order CH2 CH + CH2 H3C + CH CH3 H3C + CH2 + + CH3 + CH2 CH CH + C Bredt’s rule Stability of Alicyclic Cations ∝ + Point to Remember!! + CH2 + Rearrangement of Carbocations CH3 CH3 CH CH3 + CH2 CH3 C + CH3 Rearrangement of Carbocations + + + + Rearrangement of Carbocations + + + + + Rearrangement of Carbocations + Point to Remember!! Migrating Tendency Alkyl 1° < 2° < 3° < Phenyl < Hydride. Free Radical (CH3) Stability of Free Radical I Stability order Ph3 C Ph2 CH Ph CH2 CH3 CH2 CH CH2 CH3 CH3 CH CH3 CH3 C CH2 CH3 CH3 Carbanions ⊝ ⊝ ⊝.. Carbanions (CH3) Stability of Carbanion Stability order ⊝ ⊝ CH3 CH CH2 CH2 ⊝ Ph ⊝ Ph2CH Ph3C ⊝ CH2 ⊝ ⊝ CH2 ⊝ HC C ⊝ CHO CH2 NO2 Comparison Stability of Alkenes ∝ 𝛑 ∝ H3C H3C C C CH3 H3C CH3 H3C C 𝝰 CH CH3 H3C H3C C CH2 Bond Length Cl Cl C H I O II I II Bond Energy ∝ Dipole moment Cl Cl Cl Cl Cl Cl Basic Strength Basicity Order in the Periodic Table Example Example ≡ Basic Strength of Amines Basic Strength of 1°, 2° and 3° Amines H H H R R N N N N H R H R H R R Stability of Conjugate Acids R R N N R R H H R H H H N H R H N H H H Basic Strength of Amines in Gaseous Phase Basic Strength of Amines Electron Donating Effect of Alkyl Groups R R N N R R H H H R H N H R H Solvation Effect H N H R H R R OH2 OH2 OH2 N H R H OH2 OH2 N R R H OH2 Basic Strength in Aqueous Phase Amidines R C HN NH2 Amidines R C N H2 H N HN R R C C NH2 + H2N NH2 Resonance of Conjugate Acid + H2N R R C C NH2 H2N + NH2 Guanidine NH2 C HN N H2 C H N N H2 NH2 Resonance of Conjugate Acid NH2 NH2 C HN + H2N + H2N NH2 C NH2 NH2 + NH2 NH2 C C C NH2 H2N NH2 H2N + NH2 Steric Inhibition of Protonation H H2O H N H H OH2 H OH2 N Steric Inhibition of Protonation H H N H H H G N Steric Inhibition of Protonation ≡ Order of Basicity NH2 NH2 CH3 Steric Inhibition of Resonance (SIR) H3C H3C CH3 N CH3 General Basicity Order _ R2CH _ R3C _ NH2 _ PhCH2 _ H _ RCH2 R C _ CH3 _ Ph _ Ph3C _ Ph2CH _ C R C O _ CH2 General Basicity Order _ R CH2 _ CH3O _ RCOO CO32- _ OCN _ O _ OH _ PhO H2O _ RS _ Cl Point to Remember!! N N Acidic Strength Acidity Order in Periodic Table Point to Remember!! Order of Acidic Strength Ph SO3H R SO3H Ph COOH RCOOH OH H H2CO3 H HC HC CH NH3 H OH RCH2 OH CH2 H2C H CH3 Point to Remember!! Acidic Strength of Dicarboxylic Acids COOH (CH2)n COOH Acidic Strength of Dicarboxylic Acids COOH (CH2)n COOH COO _ (CH2)n COOH Remember!!! Ortho Effect C OH G C O G Ortho Effect C OH C O Feasibility of Reaction NaX HY NaY HX Acids that can react with NaHCO3 HCl H2SO4 HNO3 H3PO4 OH O 2N RSO3H OH NO2 NO2 RCOOH NO2 NO2 Attacking Reagents Electrophile (E+) Nucleophile (Nu ) ‒ ‒ ‒ I‒ Free Radicals Solvent Polar Protic Solvent Polar Aprotic Solvent Qualitative Analysis of an Organic Compound Quantitative Qualitative Analysis Identification of the elements present in an organic compound. Carbon and Hydrogen Nitrogen Detection of Elements Sulphur Halogens Phosphorous Detection of Carbon Carbon is detected by heating the compound with copper(II) oxide. Carbon present in the compound is oxidised to carbon dioxide. Carbon dioxide is tested with limewater, which develops turbidity. Detection of Carbon C + 2CuO CO2 + Ca(OH)2 Lime water Δ CO2 + 2Cu CaCO3 + H2O Precipitate Milky/Turbid Detection of Hydrogen Hydrogen is detected by heating the compound with copper(II) oxide. Hydrogen present in the compound is oxidised to water. Water is tested with anhydrous copper sulphate, which turns blue. Detection of Hydrogen 2H + CuO CuSO4 + 5H2O (Anhydrous) White Δ H2O + Cu CuSO4.5H2O Blue Organic Compound Δ CO2 Ca(OH)2 CaCO3 (Milky) CuO H2O CuSO4 (white) CuSO4.5H2O (Blue) Sodium Fusion Extract Elements present in the compound are converted from their covalent form to their ionic form by fusing the organic compound with sodium metal. Na + C + N 2Na + S Na + X Na + C + N + S Δ Δ Δ Δ NaCN Na2S NaX NaSCN Organic compounds are reacted with sodium to convert them into their ionic form, which is more reactive. Lassaigne’s Test Cyanide, sulphide, and halide of sodium so formed on sodium fusion are extracted from the fused mass by boiling it with distilled water. This extract is known as Sodium Fusion Extract. Detection of Nitrogen​ Sodium Fusion Extract is boiled with Iron(II) sulphate to form Sodium hexacyanoferrate (II). FeSO4 + 6NaCN Na4[Fe(CN)6]+ Na2SO4 Sodium hexacyanoferrate (II) On heating with sulphuric acid, some Fe2+ ions are oxidised to Fe3+ ions. Detection of Nitrogen​ Fe3+ reacts with Sodium hexacyanoferrate (II) to give Prussian blue colour of Ferric ferrocyanide, which confirms the presence of nitrogen. 3[Fe(CN6)] 4- + 4Fe3+ xH2O Fe4[Fe(CN)6]3.xH2O Prussian blue Test For Sulphur Lead acetate test Detection of Sulphur Sodium nitroprusside test Lead Acetate Test Sodium Fusion Extract is acidified with acetic acid and lead acetate is added to it. Na2S + (CH3COO)2Pb PbS + 2CH3COONa Black precipitate Indicates presence of S Sodium Nitroprusside Test Sodium Fusion Extract is treated with sodium nitroprusside. Na2S + Na2[Fe(CN)5NO] Na4[Fe(CN)5NOS] Violet Indicates presence of S Point to Remember!! If both nitrogen and sulphur are present in an organic compound, then sodium thiocyanate is formed, which gives blood red color with neutral FeCl3. Na + C + N + S Neutral FeCl3 + NaSCN NaSCN Fe(SCN)3 Blood red Test for Halogens​ NaCl + AgNO3 AgCl + NaNO3 White ppt NaBr + AgNO3 AgBr + NaNO3 Pale yellow ppt NaI + AgNO3 AgI + NaNO3 Yellow ppt AgCl is soluble in NH4OH AgBr is sparingly soluble in NH4OH AgI is insoluble in NH4OH Test for Halogens​ Cyanide or sulphide of sodium formed during Lassaigne’s test can interfere with silver nitrate test for halogens. Sodium fusion extract is first boiled with concentrated nitric acid to decompose them. Test for Phosphorous Compound is heated with an oxidising agent (sodium peroxide). Phosphorus present in it gets oxidised to phosphate. The solution is boiled with nitric acid and then treated with ammonium molybdate. A yellow coloration or precipitate indicates the presence of phosphorus. Test for Phosphorous Na3PO4 + 3 HNO3 H3PO4 + 12 (NH4)2MoO4 + 21 HNO3 H3PO4 + 3 NaNO3 (NH4)3PO4.12MoO3 + 21 NH4NO3 + 12 H2O yellow Quantitative Analysis Carbon and Hydrogen Nitrogen Estimation of Elements Sulphur Halogens Phosphorous Estimation of Carbon and Hydrogen A known mass of the organic compound is heated with dry copper oxide in an atmosphere of air or oxygen free from moisture and carbon dioxide. C + 2CuO 2H + CuO CO2 + 2Cu H2O + Cu Estimation of Carbon and Hydrogen CO2 produced is collected in potash bulb (containing KOH), whereas H2O is absorbed in calcium chloride tube (containing CaCI2). Estimation of Carbon and Hydrogen Pure dry O2 Sample in platinum boat CuO pallets Combustion tube Anhydrous CaCl2 Excess O2 KOH solution Estimation of Nitrogen Estimation of nitrogen Duma’s method Kjeldahl’s method Duma’s Method​ A known mass of the organic compound is heated strongly with excess of copper oxide in an atmosphere of carbon dioxide. The carbon and hydrogen are converted to CO2 and H2O. Nitrogen is set free as N2. Duma’s Method​ C + 2H + 3CuO CO2 + H2O + 3Cu Organic compound 2N + Cu N2 + Oxides of nitrogen Organic compound Oxides of nitrogen + Cu N2 + CuO Duma’s Method​ N2 is collected over the concentrated solution of KOH and its volume is measured at room temperature and atmospheric pressure. Kjeldahl’s Method​ A known mass of the organic compound containing nitrogen is heated with concentrated sulphuric acid. Nitrogen in the compound gets converted into ammonium sulphate. Organic compound + conc. H2SO4 (NH4)2SO4 Kjeldahl’s Method​ The resulting acid mixture is then heated with an excess of sodium hydroxide. Organic compound + H2SO4 (NH4)2SO4 2NaOH Na2SO4 + 2NH3 + 2H2O Kjeldahl’s Method​ The liberated ammonia gas is absorbed in a known and an excess standard solution of sulphuric acid. 2NH3 + H2SO4 (NH4)2SO4 Kjeldahl’s Method​ The amount of ammonia produced is determined by estimating the amount of sulphuric acid consumed in the reaction. The acid left unused is estimated by titration with some standard alkali. Limitations of Kjeldahl’s Method​ This method is not applicable to compounds containing nitrogen in: Nitro groups (-NO2) Azo groups (- N = N -) Nitrogen present in the ring (E.g: Pyridine) Estimation of Sulphur Sulphur is estimated as barium sulphate. The organic compound containing sulphur is taken in a Carius tube containing HNO3, where sulphur is finally converted into sulphuric acid. This sulphuric acid is passed through excess BaCl2 to get BaSO4, which is then washed, dried, & weighed. Carius Method 50 cm Sealed capillary 2 cm Fuming HNO3 AgNO3 Organic compound Carius Method Halogens are estimated as silver halides. Organic halide is treated with acidified silver nitrate solution to form silver halide, which is washed, dried, & weighed. Estimation of Phosphorus A known mass of the organic compound is heated with fuming HNO3. The phosphorus present in the organic compound is oxidised to H3PO4. The phosphoric acid, thus formed is treated with magnesia mixture to get MgNH4PO4 precipitate. The precipitate is separated, dried, and ignited to get Mg2P2O7. Estimation of Phosphorus P + 3H From organic compound + 4O From HNO3 H3PO4 + Magnesia mixture 2MgNH4PO4 H3PO4 MgNH4PO4 Mg2P2O7 + 2NH3 + H2O Purification Purification Removal of undesirable impurities associated with a particular organic compound i.e., to obtain the organic compound in pure state. Crystallisation If a saturated hot solution is allowed to cool, the solute is no longer soluble in the solvent and it forms crystals of the pure compound. The solid is filtered and dried. Crystallisation Sugar mixed with common salt can be purified using ethanol. Examples Phthalic acid mixed with naphthalene can be purified using hot water. Sublimation Certain organic substances convert directly from solid to vapour state on heating and viceversa on cooling. Solid Heat Cool Vapours Sublimation This process is very useful in the separation of a substance which sublimes on heating from a nonvolatile substance. Ex: Benzoic acid, naphthalene, anthracene, camphor, indigo, anthraquinone Differential Extraction The process of separation of an organic compound from its aqueous solution by shaking it with a suitable organic solvent. Differential Extraction The solvent should be immiscible with water and the organic compound to be separated should be highly soluble in it. Ex: Benzoic acid can be extracted from water solution using benzene. Distillation Used to purify liquids based on their difference in boiling points. Vapour Pressure and Boiling Point Vapour Pressure Boiling point Pressure exerted by the vapours over the liquid surface at equilibrium Temperature at which the vapour pressure of a liquid is equal to the external pressure Simple Fractional Types of Distillation Vacuum Steam Simple Distillation It is applied only for volatile liquids which boil without decomposing at atmospheric pressure and contains non-volatile impurities. It can also be used for separating liquids having sufficient difference in their boiling points. Simple Distillation Examples Benzene (B.P. = 80°C) and Aniline (B.P. = 184°C) Chloroform (B.P. = 61°C) and Aniline (B.P. = 184°C) Fractional Distillation If the boiling points of the liquids to be separated are closer to each other, then fractional distillation is carried out using the fractionating column. Fractional Distillation Examples Distillation of petroleum, coal tar, and crude oil Methanol (B.P. = 65°C) and Propanone (B.P. = 57°C) Benzene (B.P. = 80°C) and Toluene (B.P. = 110°C) Vacuum Distillation Distillation under reduced pressure Compounds which decompose at a temperature below their normal boiling point cannot be distilled at atmospheric pressure. On reducing the external pressure, the liquid will boil at lower temperature. Vacuum Distillation Examples Glycerine can be distilled at 180°C (B.P. = 280°C) at lower pressure Separation of glycerol from spent-lye in soap industries. Steam Distillation The liquid boils when the sum of vapour pressures due to the organic liquid (P1) and that due to water (P2) becomes equal to the atmospheric pressure. Ex: 0-, m-, p-Chlorotoluenes, o-, p-Nitrobenzene Chromatography Used for the separation, isolation, purification, and identification of components of mixtures because of the distribution of components between a liquid phase (mobile phase) and a solid phase (stationary phase). Chromatography Separation of components of a mixture takes place as a result of differential adsorption on the adsorption column. After the separation, the substances are extracted from the adsorbent using a suitable solvent, which is called eluent. Adsorption and Adsorbent Phenomenon of attracting and retaining the molecules of a substance on the surface of a liquid or a solid resulting in a higher concentration of the molecules on the surface Substance on the surface of which adsorption occurs Types of Chromatography Chromatograp Chromatography Chromatography hy Adsorption Chromatography Column Chromatography Thin Layer Chromatography Partition Chromatography Paper Chromatography Principle Based upon the differential adsorption of various components of a mixture on a suitable adsorbent Some components are more strongly adsorbed thus, travel at different rates and get separated Column Chromatography Mixture is placed on the top of the adsorbent column packed in a glass tube. An appropriate eluant, which is a liquid or a mixture of liquids is allowed to flow down the column slowly. Separation of components takes place. Thin Layer Chromatography (TLC) Involves the separation of components of a mixture over a thin layer of an adsorbent coated on a glass plate. A thin layer of an adsorbent (silica gel or alumina) is spread over the glass plate. The glass plate is known as thin layer chromatography plate or chromaplate. Thin Layer Chromatography (TLC) Relative adsorption of each component of the mixture is expressed in terms of its retardation factor i.e. Rf value Rf Distance moved by the component from baseline Distance moved by the solvent from baseline Partition Chromatography It is based on the continuous differential partitioning of components of a mixture between the stationary and the mobile phases. Paper Chromatography Principle of paper chromatography is partition chromatography, wherein, the substances are distributed or partitioned between the liquid phase and the stationary phase.