Contents Preface (v) Acknowledgements (vii) PPPART 11ART Chemical Methods used for Purification 21 Drying of Organic Compounds 21 BASICS IN ORGANIC CHEMISTRY Criteria of Purity 22 Probable Questions 24 1. Introduction to Organic Chemistry Origin of Organic Chemistry 1 3. Qualitative Analysis The Vital Force Theory “Essence of Life” 1 (Detection of Elements) Definition of Organic Chemistry 2 Introduction 25 Reasons for Treating Organic Chemistry as a Detection of Elements 25 Separate Branch of Chemistry 2 Detection of Carbon and Hydrogen 25 Rise of Organic Chemistry 5 Detection of Nitrogen 26 Need for Studying Organic Chemistry 5 Detection of Halogens 27 Classification of Organic Compounds 6 Detection of Sulphur 28 Organic Chemistry in the Service of Mankind 8 Detection of Phosphorous 28 Probable Questions 8 Detection of Metals 29 Probable Questions 29 2. Purification of Organic Compounds Introduction 9 4. Quantitative Analysis Extraction of Organic Compounds 9 Introduction 31 Estimation of Elements 31 Methods for Purification of Solids 10 Crystallization 10 Estimation of Carbon and Hydrogen 31 Fractional Crystallization 11 Estimation of Oxygen 34 Special Considerations in Crystallization 11 Estimation of Nitrogen 34 Sublimation 12 Estimation of Halogens 38 Methods for Purification of Liquids 13 Estimation of Sulphur 39 Simple Distillation 13 Estimation of Phosphorous 39 Fractional Distillation 14 Probable Questions 40 Distillation under Reduced Pressure 15 Steam Distillation 15 5. Determination of Molecular Mass Extraction with Solvent 15 Determination of Molecular Mass 41 Salting Out 16 Physical Methods 41 Counter Current Extraction 16 Victor- Meyer Method (for volatile substances) 41 Chromatography 17 Dumas Method (For non-volatile substances) 41 Adsorption Chromatography 17 Hoffman Method (For non-volatile substances) 41 Column Chromatography 17 Chemical Methods 41 Thin Layer Chromatography 18 Silver Salt Method for Acid 41 Partition Chromatography 18 Platinichloride Method for Bases 41 Paper Chromatography 19 Volumetric Method for Acids and Bases 41 Gas-Chromatography 19 Molecular Mass of Volatile Substance 41 High Performance Liquid Chromatography 20 Molecular Mass of Non-Volatile Substances 43 High-Performance Thin Layer Probable Questions 49 Chromatography (HPTLC) 21 xiv Contents 6. Nomenclature of Organic Compounds Hybridization 87 Introduction 51 Salient Features of Hybridization 87 IUPAC System of Nomenclature 51 Conditions for Hybridization 87 Steps Involved in Writing IUPAC Theory of Hybridization for the Formation of name of the Compound 58 Covalent Bond (Sidwick – Powell theory) 87 Writing the Structural Formula Source of Energy required for Hybridization 88 from the given IUPAC Name 60 Types of Hybridization 88 3 Probable Questions 61 sp Hybridization or Tetrahedral Hybridization 88 sp2 Hybridization or Trigonal Hybridization 89 7. Structure of Organic Molecules and their sp Hybridization or Diagonal Hybridization 90 Relative Properties Effectiveness of Overlap 91 Introduction to Atom/Molecule 63 Molecular Orbital Theory 91 Wave Nature of Electrons and Wave Equations 63 Bonding and Anti Bonding Orbitals 92 Quantum Mechanics 65 Relationship between Electronic Atomic Orbitals Involved in Organic Molecules 65 Configuration and Molecular Behaviour 95 Shells, Sub-Shells and Orbitals 66 Probable Questions 96 Quantum Numbers 66 8B. Influence of Structure on Shapes of Atomic Orbitals 68 Physical Properties Shape of s Orbital 68 Introduction 99 Shape of p Orbital 68 Modern Concepts of Acids and Bases 99 Rules for Distribution of Electrons into Solubility 104 Various Shells, Subshells and Orbitals 69 Solubility of Ionic Solutes 104 Probable Questions 70 Solubility of Non Ionic Solutes 104 8A. Covalent Bond Boiling Point 105 Introduction 73 Melting Point 106 The Nature of Bond between Atoms 73 Melting Point of Non-Ionic Compounds 106 Types of Bonds 73 Probable Questions 107 Ionic Bond or Electrovalent Bond 73 Covalent Bond 75 9. Factors Influencing a Chemical Reaction or Co-Ordinate Covalent Bond or Dative Bond 76 Electronic Displacements in Molecules Electronic Theory of Valency 77 Introduction 109 Characteristic Property of Covalent Bond 77 Inductive Effect 109 Bond Length 77 Types of Inductive Effect 110 Mesomeric and Resonance Effect 111 Bond Angle 78 Bond Energy 79 Electromeric Effect 113 Bond Breaking 80 Resonance 115 Bond Order 80 Hyperconjugation 117 Polarity of Bond and Dipole Moments 80 Probable Questions 119 Applications of Dipole Moment 83 10. Hydrogen Bonding Intramolecular Forces 84 Introduction 121 Inter molecular Forces 84 Types of Hydrogen Bonding 122 Types of Orbital Overlapping and their Intermolecular Hydrogen Bonding 122 Orbital Diagrams 85 Intramolecular Hydrogen Bonding 123 s-s Overlapping 85 Effect of Hydrogen Bonding 123 s-p Overlapping 85 Impact of Hydrogen Bonding in Biology 126 p-p Overlapping 86 Probable Questions 127 Contents xv 11. Organic Reactions and Mechanism PART 2 Introduction 129 ALIPHATIC COMPOUNDS Bond Breaking (Homolysis and Heterolysis) 129 Homolysis 129 14. Alkanes Heterolysis 130 Introduction 215 Organic Reagents Importance of Alkanes 215 (Nucleophiles and Electrophiles) 130 Nomenclature of Alkanes 216 Nucleophiles (Nucleous Loving Species or General Methods of Preparation 220 Electron Rich Species) 130 Electrophiles (Electron Loving Species or Summary of General Methods of Electron Deficient Species) 130 Preparation of Alkanes 223 Types of Organic Reactions 131 Physical Properties 224 Substitution Reactions 131 Structure 224 Addition Reactions 132 Chemical Properties 224 Elimination Reactions 133 Summary of Chemical Reactions 230 Rearrangement Reactions 133 Pyrolysis or Cracking of Alkanes 230 Reaction Mechanisms 134 Conformations of Alkanes 231 Kinetics of Reactions 134 Individual Members 232 Reaction Progress 135 Methane or Marsh Gas 232 Reactive Intermediates or Reaction Intermediates 137 Probable Questions 234 Carbonium Ions or Carbocations 138 Reactions of Carbocations or 15. Alkenes or Olefins Fate of Carbocations 143 Introduction 235 Carbanions 145 Importance of Alkenes 235 Carbon Free Radicals 146 Nomenclature 237 Carbenes 148 Isomerism 238 Nitrenes or Imidogens 149 General Methods of Preparation 238 Vinylamines or Enamines or Summary of Methods of Preparation 241 α,β-Unsaturated Amines 151 Structure 241 Probable Question 152 Physical Properties 242 12. Isomerism Chemical Properties of Alkenes 242 Introduction 153 Summary of Reactions of Alkenes 259 Types of Isomerism 153 Individual Members 260 Ethylene 260 Structural Isomerism or Constitutional Isomerism 154 Probable Questions 261 Stereoisomerism 157 Geometrical Isomerism 158 16. Alkynes or Acetylenes Optical Isomerism 162 Introduction 263 Nomenclature of Enantiomers or the Importance of Alkynes 263 R, S-System or Nomenclature or R and Nomenclature 264 S Notation of Optical Isomers 163 Isomersim 265 Measurement of Optical Activity 168 General Methods of Preparation 265 Racemic Modification 170 Summary of Methods of Preparation 267 Walden Inversion 171 Physical Properties 268 Resolution or Separation of Racemic Mixture 172 Structure 268 Asymmetric Synthesis 173 Acidity of Terminal Alkynes 268 Tautomerism 174 Chemical Properties 269 Probable Questions 176 Summary of Chemical Reactions 274 13. General Terms used in Organic Chemistry Individual Members 275 General Terms Like Homologues Series 179 Acetylene 275 xvi Contents Physical Properties 276 Monohydric Alcohols 319 Chemical Properties 276 Introduction 319 Probable Questions 279 Classification 319 Nomenclature 320 17. Alkadienes or Dienes or Diolefins General Methods of Preparation 321 Introduction 281 Summary of Methods of Preparation 327 Importance of Alkadienes 281 Physical Properties 328 Nomenclature 282 Chemical Properties 328 Butadiene 284 Structure 328 Summary of Methods of Preparation 285 Reactions Involving Replacement of Relative Stability of Dienes 285 Hydrogen of the Hydroxyl Group 329 Stability of Conjugated Dienes 286 Reactions Involving Replacement of Summary of Chemical Reactions 295 Hydroxyl Group 330 Theory of Resonance 295 Reactions Involving both Alkyl Group and Resonance Stabilisation of Hydroxyl Group 331 Allyl Radicals - Hyper Conjugation 297 Chemical Tests for Alcohols 332 Nucleophilic Substitution in Allylic Substrates: Distinction between Primary, S 1 Reactivity and Allylic Rearrangement 298 N Secondary and Tertiary Alcohols 333 Nucleophilic Substitution in Allylic Substrates 299 Summary of Chemical Reactions 335 Probable Questions 299 Individual Members of Monohydric Alcohols 336 Methanol or Wood Alcohol 336 18. Cycloalkanes Ethanol or Grain Alcohol 336 Introduction 301 Dihydric Alcohols (or) Diols 340 Importance of Cycloalkanes 301 Introduction 340 Nomenclature 302 Nomenclature 340 General Methods of Preparation 303 General Methods of Preparation of Physical Properties 305 Ethylene Glycol 341 Chemical Properties 305 Physical Properties 341 Summary of Chemical Reactions 307 Chemical Properties 341 Bayer’s Strain Theory or Stability of Trihydric Alcohols (or) Triols 344 Cycloalkanes or Ring Strain 308 Introduction 344 Molecular Orbital Theory of Cycloalkanes 309 General Methods of Preparation 345 Type of Strains 310 Physical Properties 346 Sache-Mohr Theory 310 Chemical Properties 346 Structure of Two Forms of Cyclohexane 310 Pharmaceutically Important Alcohols 349 Conformations of Cycloalkanes 311 Nitroglycerin 349 Drawing Chair Form of Cyclohexane Ring 311 Unsaturated Alcohols 350 Interconversion of Conformations of Vinyl Alcohol 350