Andrew F.Parsons KEYNOTES IN Organic Chemistry SECOND EDITION WILEY
17mm 246 x 189 SECOND EDITION SECOND EDITION Andrew F. Parsons Andrew F. Parsons Organic Chemistry Organic Chemistry KEYNOTES IN KEYNOTES IN This concise and accessible textbook provides notes for students studying chemistry and related courses at undergraduate level, covering core organic chemistry in a format ideal for learning and rapid revision. The material, with an emphasis on pictorial presentation, is organised to provide an overview of the essentials of functional group chemistry and reactivity, leading the student to a solid understanding of the basics of organic chemistry. This revised and updated second edition of Keynotes in Organic Chemistry includes: • new margin notes to emphasise links between different topics, • colour diagrams to clarify aspects of reaction mechanisms and illustrate key points, and • a new keyword glossary. In addition, the structured presentation provides an invaluable framework to facilitate the rapid learning, understanding and recall of critical concepts, facts and definitions. Worked examples and questions are included at the end of each chapter to test the reader’s understanding. Reviews of the First Edition “ …this text provides an outline of what should be known and understood, including fundamental concepts and mechanisms.” Journal of Chemical Education, 2004 “ Despite the book’s small size, each chapter is thorough, with coverage of all important reactions found at first-year level... ideal for the first-year student wishing to revise… and priced and designed appropriately.” The Times Higher Education Supplement, 2004 Department of Chemistry, University of York, UK SECOND EDITION Parsons Organic Chemistry KEYNOTES IN GREEN BOX RULES ARE FOR PROOF STAGE ONLY. DELETE BEFORE FINAL PRINTING
Contents Preface 1 Structure and bonding 1 nc versus covalent bonds The octet rule Formal charge Sigma(-)and pi(-)bonds Hybridisation 22346 1.6 Inductive effects,hyperconjugation and mesomeric effects 1.6.1 Inductive effects Hyperconjugation 1.6.3 Mesomeric effects 1.7 Acidity and basicity 6779 1.7.1 Acids 1.72 Bases 1.7.3 Lewis acids and bases 912155 1.7.4 Basicity and hybridisation 1.7.5 Acidity and aromaticity 6 1.7.6 Acid-base reactions Worked example 17 Problems 1 2 Functional nomenclature and drawing organic compo groups 23 Alkyl an aryl groups 2.4 Alkyl subs 241 2.5 Drawing organic structures 112335289 rked example Problems 3.1 Isomerism 31 3.2 Confo 3.21 onal isomers of ethane(CH,CH3) 32 3.2.2 of e(CH,CH2CH2CH3) 3 3.2.3 Conformations of eycloalkanes 34
Contents Preface xi 1 Structure and bonding 1 1.1 Ionic versus covalent bonds 1 1.2 The octet rule 2 1.3 Formal charge 2 1.4 Sigma (s) and pi (p) bonds 3 1.5 Hybridisation 4 1.6 Inductive effects, hyperconjugation and mesomeric effects 6 1.6.1 Inductive effects 6 1.6.2 Hyperconjugation 7 1.6.3 Mesomeric effects 7 1.7 Acidity and basicity 9 1.7.1 Acids 9 1.7.2 Bases 12 1.7.3 Lewis acids and bases 15 1.7.4 Basicity and hybridisation 15 1.7.5 Acidity and aromaticity 16 1.7.6 Acid-base reactions 16 Worked example 17 Problems 18 2 Functional groups, nomenclature and drawing organic compounds 21 2.1 Functional groups 21 2.2 Alkyl and aryl groups 22 2.3 Alkyl substitution 23 2.4 Naming carbon chains 23 2.4.1 Special cases 25 2.5 Drawing organic structures 27 Worked example 28 Problems 29 3 Stereochemistry 31 3.1 Isomerism 31 3.2 Conformational isomers 32 3.2.1 Conformations of ethane (CH3CH3) 32 3.2.2 Conformations of butane (CH3CH2CH2CH3) 33 3.2.3 Conformations of cycloalkanes 34
vi Contents 3.2.4 Cycloh xane 3.3 Con nfigurational isomers 33. Alkenes 3.32 Isomers with chiral centres Worked example 1537378415 Problems 4 Reactivity and mechanism A1 s:ions 42.1 4.3 and carbon radicals 431 Order A 4.6 al 4.62 s(involving ionic intermediates) 4.63 reaction: 4.7 electivity 4.9 thermodynamics and kinetics 4.9 hermodynamics 9912345566899060666 Kinetic versus thermodynamic control 4.100r ital overlap and energy 4.11 Guidelines for drawing reaction mechanisms Worked example Problems 5 Halog oalkanes 73 51 ucture 52.2 logenation of alka ogena 5.2.3 53 substitution 5.32 Nucleophilic 533 titution versus elimination 34437888992 Worked example Problems 6 Alkenes and alkynes 61 5 6.2 97
3.2.4 Cyclohexane 35 3.3 Configurational isomers 37 3.3.1 Alkenes 37 3.3.2 Isomers with chiral centres 38 Worked example 44 Problems 45 4 Reactivity and mechanism 49 4.1 Reactive intermediates: ions versus radicals 49 4.2 Nucleophiles and electrophiles 51 4.2.1 Relative strength 52 4.3 Carbocations, carbanions and carbon radicals 53 4.3.1 Order of stability 54 4.4 Steric effects 55 4.5 Oxidation levels 55 4.6 General types of reaction 56 4.6.1 Polar reactions (involving ionic intermediates) 56 4.6.2 Radical reactions 58 4.6.3 Pericyclic reactions 59 4.7 Ions versus radicals 59 4.8 Reaction selectivity 60 4.9 Reaction thermodynamics and kinetics 60 4.9.1 Thermodynamics 60 4.9.2 Kinetics 62 4.9.3 Kinetic versus thermodynamic control 65 4.10 Orbital overlap and energy 65 4.11 Guidelines for drawing reaction mechanisms 67 Worked example 68 Problems 69 5 Halogenoalkanes 73 5.1 Structure 73 5.2 Preparation 74 5.2.1 Halogenation of alkanes 74 5.2.2 Halogenation of alcohols 75 5.2.3 Halogenation of alkenes 77 5.3 Reactions 78 5.3.1 Nucleophilic substitution 78 5.3.2 Elimination 84 5.3.3 Substitution versus elimination 89 Worked example 91 Problems 92 6 Alkenes and alkynes 95 6.1 Structure 95 6.2 Alkenes 97 vi Contents
Contents vii 6.21 Preparation 97 622 Reactions 98 6.3 Alkynes 631 Preparation 110 6.3.2 Reactions 110 Worked example 113 Problems 7 Benzenes 117 7.1 Structure 117 7.2 Reactions 119 721 Halogenation 119 722 Nitration 120 7.23 Sulfonation 120 7.24 Alkylation:The Friedel-Crafts alkylation 7.25 Acylation:The Friedel-Crafts acylation 122 7.3 Reactivity of substituted benzenes 123 7.3.1 Reactivity of benzene rings:Activating and deactivating substituents 7.3.2 Orientation of reactions 125 14 Nucleophilic aromatic substitution (the SxAr mechanism) 127 The formation of benzyne Transformation of side chains 129 Reduction of the benzene ring 132 7.8 The synthesis of substituted benzenes 132 79 Electrophilic substitution of naphthalene 135 7.10 Electrophilic substitution of pyridine 135 7.11 Electrophilic substitution of 136 Worked example 136 Problems 137 8 Carbonyl compounds:aldehydes and ketones 139 81 Structure 139 8. Reactivity 140 8.3 Nucleophilic addition reactions 142 8.3.1 Relative reactivity of aldehydes and ketones 142 8.3.2 Types of nucleophiles 142 8.3.3 Nucleophilic addition of hydride:reduction 143 8.3.4 Nucleophilic addition of carbon nucleophiles formation of C-C honds 146 8.3.5 Nucleophilic addition of oxygen nucleophiles: formation of hydrates and acetals 149 8.3.6 Nucleophilic addition of sulfur nucleophilesa formation of thioacetals 151 8.3.7 Nucleophilic addition of amine nucleophiles: formation of imines and enamines 152
6.2.1 Preparation 97 6.2.2 Reactions 98 6.3 Alkynes 110 6.3.1 Preparation 110 6.3.2 Reactions 110 Worked example 113 Problems 114 7 Benzenes 117 7.1 Structure 117 7.2 Reactions 119 7.2.1 Halogenation 119 7.2.2 Nitration 120 7.2.3 Sulfonation 120 7.2.4 Alkylation: The Friedel-Crafts alkylation 121 7.2.5 Acylation: The Friedel-Crafts acylation 122 7.3 Reactivity of substituted benzenes 123 7.3.1 Reactivity of benzene rings: Activating and deactivating substituents 124 7.3.2 Orientation of reactions 125 7.4 Nucleophilic aromatic substitution (the SNAr mechanism) 127 7.5 The formation of benzyne 128 7.6 Transformation of side chains 129 7.7 Reduction of the benzene ring 132 7.8 The synthesis of substituted benzenes 132 7.9 Electrophilic substitution of naphthalene 135 7.10 Electrophilic substitution of pyridine 135 7.11 Electrophilic substitution of pyrrole, furan and thiophene 136 Worked example 136 Problems 137 8 Carbonyl compounds: aldehydes and ketones 139 8.1 Structure 139 8.2 Reactivity 140 8.3 Nucleophilic addition reactions 142 8.3.1 Relative reactivity of aldehydes and ketones 142 8.3.2 Types of nucleophiles 142 8.3.3 Nucleophilic addition of hydride: reduction 143 8.3.4 Nucleophilic addition of carbon nucleophiles: formation of CC bonds 146 8.3.5 Nucleophilic addition of oxygen nucleophiles: formation of hydrates and acetals 149 8.3.6 Nucleophilic addition of sulfur nucleophiles: formation of thioacetals 151 8.3.7 Nucleophilic addition of amine nucleophiles: formation of imines and enamines 152 Contents vii
Contents 84 Keto-enol tautomerism Reactivity of enols Acidity of a-hydrogen atoms:enolate ion formation 8.4.4 Reactivity of enolates 1555151580 85 Carbonyl-carbonyl condensation reactions 8.5.1 Condensations of aldehydes and ketones: the aldol condensation reaction 8.52 Crossed or mixed aldol condensations 18 8.53 Intramolecular aldol reactions 8.5.4 The Michael reaction Worked example Problems 6116 0 nds:carboxylic acids and derivatives 9.3 acyl substitutior reactions 66666 acid derivatives derivatives arboxylc acids 169 9.3.3 ersus 9.4 Preparation of esters (esterification) Nucleophilic substitution reactions of acid chloride Nucleophilic substitution reactions of acid anhydrides 9.7 Nucleophilic substitution reactions of esters 9.8 Nucleophilic substitution and reduction reactions of amides Nucleophilic addition reactions of nitriles 9.10 a-Substitution reactions of carboxylic acids 9.11 Carbonyl-carbonyl condensation reactions 9.11.1 The Claisen condensation reaction 9 Crossed or mixed Claisen condensations 18 Intramolecular Claisen condensations: the Dieckmann reaction 9.12 A summary of carbonyl reactivity Worked example Problems 10 10. spectrometry (MS) 10. Introduction 10.1 10.1.3 Determination of molecular formula
8.4 a-Substitution reactions 156 8.4.1 Keto-enol tautomerism 156 8.4.2 Reactivity of enols 157 8.4.3 Acidity of a-hydrogen atoms: enolate ion formation 157 8.4.4 Reactivity of enolates 158 8.5 Carbonyl-carbonyl condensation reactions 160 8.5.1 Condensations of aldehydes and ketones: the aldol condensation reaction 160 8.5.2 Crossed or mixed aldol condensations 161 8.5.3 Intramolecular aldol reactions 162 8.5.4 The Michael reaction 163 Worked example 164 Problems 165 9 Carbonyl compounds: carboxylic acids and derivatives 167 9.1 Structure 167 9.2 Reactivity 168 9.3 Nucleophilic acyl substitution reactions 168 9.3.1 Relative reactivity of carboxylic acid derivatives 168 9.3.2 Reactivity of carboxylic acid derivatives versus carboxylic acids 169 9.3.3 Reactivity of carboxylic acid derivatives versus aldehydes/ketones 169 9.4 Nucleophilic substitution reactions of carboxylic acids 170 9.4.1 Preparation of acid chlorides 170 9.4.2 Preparation of esters (esterification) 170 9.5 Nucleophilic substitution reactions of acid chlorides 171 9.6 Nucleophilic substitution reactions of acid anhydrides 172 9.7 Nucleophilic substitution reactions of esters 173 9.8 Nucleophilic substitution and reduction reactions of amides 175 9.9 Nucleophilic addition reactions of nitriles 176 9.10 a-Substitution reactions of carboxylic acids 178 9.11 Carbonyl-carbonyl condensation reactions 178 9.11.1 The Claisen condensation reaction 178 9.11.2 Crossed or mixed Claisen condensations 179 9.11.3 Intramolecular Claisen condensations: the Dieckmann reaction 180 9.12 A summary of carbonyl reactivity 181 Worked example 182 Problems 183 10 Spectroscopy 185 10.1 Mass spectrometry (MS) 185 10.1.1 Introduction 185 10.1.2 Isotope patterns 187 10.1.3 Determination of molecular formula 188 viii Contents
Contents ix 10.1.4 Fragmentation patterns 10.1.5 Chemical ionisation(CD 10.2 The electromagnetic spectrum 10.3 Ultraviolet(UV)spectroscopy 10.4 Infrared (IR)spec oscopy 10.5 Nuclear magnetic resonance(NMR)spectroscopy 10.5.1 10.5.2 copy Worked example Problems 11 Natural products and synthetic polymers 11.1 Carbohydrates 11.2 Lipids 11.2.1 Waxes,fats and oils 11.2.2 Steroids 00010 11.3 Amino acids.peptides and proteins 1 11.4 Nucleic acids 213 11.5 Synthetic polymers 11.5.1 Addition polymers 11.5.2 Condensation polymers Worked example Problems Appendix 1:Bond dissociation enthalpies Appendix 2:Bond lengths Appendix 3:Approximate pKa values (relative to water) 2 Appendix 4:Useful abbreviations Appendix 5:Infrared absorptions 29 Appendix 6:Approximate NMR chemical shifts Appendix 7:Reaction summaries Appendix 8:Glossary 241 Further reading 2 Outline answer Index
10.1.4 Fragmentation patterns 188 10.1.5 Chemical ionisation (CI) 189 10.2 The electromagnetic spectrum 189 10.3 Ultraviolet (UV) spectroscopy 190 10.4 Infrared (IR) spectroscopy 192 10.5 Nuclear magnetic resonance (NMR) spectroscopy 194 10.5.1 1H NMR spectroscopy 197 10.5.2 13C NMR spectroscopy 202 Worked example 203 Problems 205 11 Natural products and synthetic polymers 207 11.1 Carbohydrates 207 11.2 Lipids 209 11.2.1 Waxes, fats and oils 209 11.2.2 Steroids 210 11.3 Amino acids, peptides and proteins 211 11.4 Nucleic acids 213 11.5 Synthetic polymers 214 11.5.1 Addition polymers 215 11.5.2 Condensation polymers 217 Worked example 218 Problems 219 Appendix 1: Bond dissociation enthalpies 221 Appendix 2: Bond lengths 223 Appendix 3: Approximate pKa values (relative to water) 225 Appendix 4: Useful abbreviations 227 Appendix 5: Infrared absorptions 229 Appendix 6: Approximate NMR chemical shifts 231 Appendix 7: Reaction summaries 235 Appendix 8: Glossary 241 Further reading 249 Outline answers 251 Index 277 Contents ix
Preface With the advent of modularisation and an eve reasing number of examina tions,ther ing ne ed fo otes that caps ulate the e ide for related emistry) in the UK.The text will also be appropria similar c oude ced ng t material pictorially (pictures eak word nce. latively few paragrap of text bu e are ann key phras /key inf ciples efinition ed to provide a struct red programme of revision Fu dament 1g, ona stry ar ntro important c of the e ity and m I to prov the reade ummary of the organi The ai ere Is pro which are nec following an em materia based on rea Inus,an o 2 rea an mechanisms are revisite in more de e follo chapters.Chapters 5-10 are treated essentially as 'case studies',reviewing the chemistry of the most important functional groups.Halogenoalkanes are discussed first and as these compounds undergo elimination reactions this is followed by the (electrophilic addition)reactions of alkenes and alkynes.This leads on to the contrasting (electrophilic substitution)reactivity of benzene and derivatives in Chapter 7.while the rich chemistry of carbonyl compounds is divided into Chapters 8 and 9.This division is made on the basis of the different reactivity (addition versus substitution)of aldehydes/ketones and carboxylic acid derivatives to nucleophiles.A chapter is included to revise the importance of spectroscopy in structure elucidation and,finally,the structure and reactivity of a number of important natural products and synthetic polymers is highlighted in Chapter 11.Worked examples and questions are included at the end of each chapter to test the reader's understanding,and outline answers are provided for all of the questions.Tables of useful physical data,reaction summaries and a glossary are included in appendices at the back of the book
Preface With the advent of modularisation and an ever-increasing number of examinations, there is a growing need for concise revision notes that encapsulate the key points of a subject in a meaningful fashion. This keynote revision guide provides concise organic chemistry notes for first year students studying chemistry and related courses (including biochemistry) in the UK. The text will also be appropriate for students on similar courses in other countries. An emphasis is placed on presenting the material pictorially (pictures speak louder than words); hence, there are relatively few paragraphs of text but numerous diagrams. These are annotated with key phrases that summarise important concepts/key information and bullet points are included to concisely highlight key principles and definitions. The material is organised to provide a structured programme of revision. Fundamental concepts, such as structure and bonding, functional group identification and stereochemistry are introduced in the first three chapters. An important chapter on reactivity and mechanism is included to provide a short overview of the basic principles of organic reactions. The aim here is to provide the reader with a summary of the ‘key tools’ which are necessary for understanding the following chapters and an important emphasis is placed on organisation of material based on reaction mechanism. Thus, an overview of general reaction pathways/mechanisms (such as substitution and addition) is included and these mechanisms are revisited in more detail in the following chapters. Chapters 5–10 are treated essentially as ‘case studies’, reviewing the chemistry of the most important functional groups. Halogenoalkanes are discussed first and as these compounds undergo elimination reactions this is followed by the (electrophilic addition) reactions of alkenes and alkynes. This leads on to the contrasting (electrophilic substitution) reactivity of benzene and derivatives in Chapter 7, while the rich chemistry of carbonyl compounds is divided into Chapters 8 and 9. This division is made on the basis of the different reactivity (addition versus substitution) of aldehydes/ketones and carboxylic acid derivatives to nucleophiles. A chapter is included to revise the importance of spectroscopy in structure elucidation and, finally, the structure and reactivity of a number of important natural products and synthetic polymers is highlighted in Chapter 11. Worked examples and questions are included at the end of each chapter to test the reader’s understanding, and outline answers are provided for all of the questions. Tables of useful physical data, reaction summaries and a glossary are included in appendices at the back of the book
xii Preface New to this edition A number of additions have been made to this edition to reflect the feedback from students and lecturers A second colour is used to clarify some of the diagrams.particularly the chanisticaspecsadedinthemargintohelpthereadlerfadnfomatonat Reference note to emphasise links between differento ms are included in the introducto Additional end-of-chapte rykey point for each chapter oblems (with outlin rs)are included .A worked example is included at the end of each chapter 。The informatio in the appendices has been expanded,including reaction summaries and a glossary Acknowledgements eople I would like to thank for their help with this projec rk.The also like t nstructive comm s p ald lik e to aul r n arah Tilley from Wiley,for all their help in progressing the second edition. Dr Andrew F.Pars 20153
New to this edition A number of additions have been made to this edition to reflect the feedback from students and lecturers: A second colour is used to clarify some of the diagrams, particularly the mechanistic aspects Reference notes are added in the margin to help the reader find information and to emphasise links between different topics Diagrams are included in the introductory key point sections for each chapter Additional end-of-chapter problems (with outline answers) are included A worked example is included at the end of each chapter The information in the appendices has been expanded, including reaction summaries and a glossary Acknowledgements There are numerous people I would like to thank for their help with this project. This includes many students and colleagues at York. Their constructive comments were invaluable. I would also like to thank my family for their support and patience throughout this project. Finally, I would like to thank Paul Deards and Sarah Tilley from Wiley, for all their help in progressing the second edition. Dr Andrew F. Parsons 2013 xii Preface
Structure and bonding Key point.Organic chemistry is the study of carbon compounds.lonic bonds involve elements gaining or losing electrons but the carbon atom is able to form four covalent bonds by sharing the four electrons in its outer shell.Single (C-C). double (C=C)or triple bonds(C=C)to carbon are possible.When carbon is bonded to a different element,the electrons are not shared equally.as electro- negative atoms (or groups)attract the electron density whereas electropositive atoms (or groups)repel the electron density.An understanding of the electron- withdrawing or-donating ability of atoms,or a group of atoms,can be used to predict whether an organic compound is a good base. resonance stabilisation of the allyl cation by inductive effed 8一H8入 e -H +M group three+lgroups 1.1 lonic versus covalent bonds lonic bonds are formed between molecules with opposite charges.The nega- eheernaianateondytheadeaia e.g.Na Covalent bonds are formed when a pair of electrons is shared between two atoms.A single line represents the two-electron bond. 0 Atom sg.GI-CI=。gag Aom— 0000
1 Structure and bonding Key point. Organic chemistry is the study of carbon compounds. Ionic bonds involve elements gaining or losing electrons but the carbon atom is able to form four covalent bonds by sharing the four electrons in its outer shell. Single (CC), double (CC) or triple bonds (CC) to carbon are possible. When carbon is bonded to a different element, the electrons are not shared equally, as electronegative atoms (or groups) attract the electron density whereas electropositive atoms (or groups) repel the electron density. An understanding of the electronwithdrawing or -donating ability of atoms, or a group of atoms, can be used to predict whether an organic compound is a good acid or base. CH2 H2C resonance stabilisation of the allyl cation +M group Et Et N Et H three +I groups conjugate acid of Et3N is stabilised by inductive effects 1.1 Ionic versus covalent bonds Ionic bonds are formed between molecules with opposite charges. The negatively charged anion will electrostatically attract the positively charged cation. This is present in (inorganic) salts. Cation Anion e.g. Na Cl Covalent bonds are formed when a pair of electrons is shared between two atoms. A single line represents the two-electron bond. Atom Atom Cl Cl e.g. o o o o o o Cl o o o o o o Cl o o Keynotes in Organic Chemistry, Second Edition. Andrew F. Parsons. 2014 John Wiley & Sons, Ltd. Published 2014 by John Wiley & Sons, Ltd.
2 Structure and bonding Coordinate for dative)bonds are formed when a pair of electrons is shared between two atoms.One atom donate s both electrons and a single line or an arrow represents the two-electron bond. THF)a electron acceptor O→BH or 8_8 electron donor .Hydrogen bonds are formed when the partially positive (+)hydrogen of one molecule interacts with the partially negative(-)heteroatom (e.g.oxygen or nitrogen)of another molecule. Molecueeteratom-MolealeHH 1.2 The octet rule To forondthe cabon atom shares electrons to give a stablell shell'elec ration of eight t valence electrons Methane is the smallest alkane- alkanes are a family of Methane(CHa) H8valence electrons H Section 2.4) G。+4 Hx-H2C2H=H-C-H H Lewis structure ral C is in group 14 and so has 4 valence electrons A line =2 electrons H is in group 1 and so has 1 valence electron A single bond contains two electrons,a double bond contains four electrons and a triple bond contains six electrons.A lone(or non-bonding)pair of electrons is represented by two dots () Carbon dioxide (CO) Hydrogen cyanide (HCN) 6:c竖d=0=c=g HCN文三H-C三N 1.3 Formal charge Formal positive or negative charges are assigned to atoms,which have an apparent 'abnormal'number of bonds
Coordinate (or dative) bonds are formed when a pair of electrons is shared between two atoms. One atom donates both electrons and a single line or an arrow represents the two-electron bond. O BH3 or O BH3 electron donor electron acceptor Hydrogen bonds are formed when the partially positive (dþ) hydrogen of one molecule interacts with the partially negative (d) heteroatom (e.g. oxygen or nitrogen) of another molecule. Molecule–H Heteroatom–Molecule e.g. HO H δ+ δ– δ+ δ– OH2 1.2 The octet rule To form organic compounds, the carbon atom shares electrons to give a stable ‘full shell’ electron configuration of eight valence electrons. H CH H H H CH H H o o o o + 4 H Methane (CH4) Lewis structure Full structural formula (or Kekulé structure) A line = 2 electrons 8 valence electrons C is in group 14 and so has 4 valence electrons X X X X C o X o o o H is in group 1 and so has 1 valence electron A single bond contains two electrons, a double bond contains four electrons and a triple bond contains six electrons. A lone (or non-bonding) pair of electrons is represented by two dots ( ). Carbon dioxide (CO2) Hydrogen cyanide (HCN) OCO o oo o H C N oo o o C X XXX O O XX XX XX XX C N X X H X X X X 1.3 Formal charge Formal positive or negative charges are assigned to atoms, which have an apparent ‘abnormal’ number of bonds. The cyclic ether is tetrahydrofuran (THF) and BH3 is called borane (Section 6.2.2.5) Intramolecular hydrogen bonding in carbonyl compounds is discussed in Section 8.4.1 Methane is the smallest alkane – alkanes are a family of compounds that contain only C and H atoms linked by single bonds (Section 2.4) Drawing organic compounds using full structural formulae and other conventions is discussed in Section 2.5 2 Structure and bonding