vi
CONTENTS
2.9.6
Aromatic heterocycles
44
2.9.7
Fused rings
44
2.10 Resonance structures and curly arrows
45
2.11 Hydrogen bonding
49
2.12 Molecular models
51
3
Stereochemistry
55
3.1
Hybridization and bond angles
55
3.2
Stereoisomers
56
3.3
Conformational isomers
57
3.3.1
Conformations of acyclic compounds
57
3.3.2
Conformations of cyclic compounds
60
3.4
Configurational isomers
73
3.4.1
Optical isomers: chirality and optical activity
73
3.4.2
Cahn–Ingold–Prelog system to describe configuration
at chiral centres
80
3.4.3
Geometric isomers
83
3.4.4
Configurational isomers with several chiral centres
85
3.4.5
Meso compounds
90
3.4.6
Chirality without chiral centres
92
3.4.7
Prochirality
94
3.4.8
Separation of enantiomers: resolution
99
3.4.9
Fischer projections
100
3.4.10
D and L configurations
103
3.5
Polycyclic systems
106
3.5.1
Spiro systems
106
3.5.2
Fused ring systems
107
3.5.3
Bridged ring systems
116
4
Acids and bases
121
4.1
Acid–base equilibria
121
4.2
Acidity and pK a values
122
4.3
Electronic and structural features that influence acidity
125
4.3.1
Electronegativity
125
4.3.2
Bond energies
125
4.3.3
Inductive effects
125
4.3.4
Hybridization effects
128
4.3.5
Resonance/delocalization effects
129
4.4
Basicity
135
4.5
Electronic and structural features that influence basicity
136
4.5.1
Electronegativity
136
4.5.2
Inductive effects
137
4.5.3
Hybridization effects
138
4.5.4
Resonance/delocalization effects
139
4.6
Basicity of nitrogen heterocycles
143
4.7
Polyfunctional acids and bases
144
4.8
pH
146
4.9
The Henderson–Hasselbalch equation
149