Molecular structure and reactivity (CH2103)
This module aims to give an understanding of the major principles involved in organic chemistry - covering the fundamentals of bonding (using VSEPR and hybridisation arguments) , structure and stereochemistry, leading to a description of the types of reaction and reactivity of the various structural types. These principles are then illustrated by a range of essential reactions, laying the foundation for further organic chemistry.
This module will provide the student with an understanding of the link between molecular structure and reactivity. Consideration will be given to the relationship between molecular formula and isomerism as well as the prediction of structure and molecular shape using VSEPR and hybridisation (sp, sp2, sp3 etc) of atomic orbitals. The characteristic properties of organic functional groups and the role of resonance and inductive effects in molecules will be discussed in relationship to their reactivity. The structure of simple biological molecules and simple heterocyclic structures. Common reaction mechanisms such as acid/base, SN1, SN2, E1 and E2 will be introduced along with mechanisms involving carbonyls such as C-C bond formation and oxidation/reduction in organic chemistry.
Molecular structures, shape and behaviour :
- Consequences of bonding ( MO and hybridisation description).Bond lengths and angles; covalent and Van der Waals radii.
- Stereoisomerism - enantiomers, resonance structures, CIP rules. Conformation - alkanes, simple cyclic compounds.Â Nomenclature physical properties. Molecular shape and bonding in unsaturated systems including aromatic rings. Cis/trans isomers.
- Energetics - energy diagrams, transition states, intermediates, radical reactions.
- Reaction classification - homolytic, heterolytic, pericyclic processes. Reactive intermediates - carbonium ions, carbanions, carbon radicals; ease of formation. Nucleophiles and electrophiles. Use of arrows to represent electron movements. Inductive effects. Delocalisation of π-electrons - resonance and representation of resonance.
Typical reactions of functional groups :
Description of the major functional groups in organic chemistry and description of their associated properties :
- Acidity-basicity (including amines, pyridines) and electrophilicity-nucleophilicity.
- Substitution - homolytic (alkanes and alkylbenzenes);
- nucleophilic at saturated carbon (alkyl halides and protonated alcohols), SN1 and SN2 mechanisms; at unsaturated carbon (carboxylic acid derivatives); electrophilic (introduction to benzene substitution).
- Eliminations; nucleophilic at unsaturated carbon (carboxylic acids and their derivatives); electrophilic (monosubstituted benzenes).
- Addition - nucleophilic (aldehydes, ketones, nitriles); electrophilic (alkenes, Markovnikov).
Practical work :
Experiments to practice the basic manipulations in organic chemistry :
Preparations of typical crystalline solids - e.g. acetanilide - and the associated work-up and purification procedures.
Isolation of a natural organic compound on a small scale - trimyristin.
Small-scale experiments to illustrate the properties of the major functional groups, and the use of these methods to identify unknown compounds.