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Synthetic chemistry (CH2107)

Aims

The module aims to describe major synthetic procedures in aliphatic and aromatic organic chemistry, and to give an appreciation of the factors involved in selecting a procedure for a particular purpose, and linking procedures to give a required transformation.

General description

This module develops ideas introduced in CH2103, following a detailed treatment of functional groups. It describes the main procedures for the synthesis of organic substances, covering methods for the inter-conversion of functional groups, for C-C bond formation, and for introduction of substituents into aromatic rings. Reactions are described in terms of electronic mechanism, with stereochemical factors where appropriate, and will include examples of alkenes and aromatics in addition, substitution and Diels-Alder reactions.

Practical work includes the preparation of organic compounds using the transformations described above, methods to follow the progress of reactions and the identification of reaction products.

Syllabus content

Functional group chemistry :

Outline of reasons for synthesis and synthetic planning.

Functional Group Interconversions:

Definition of oxidation series of functional groups.

  • Oxidation of alkenes - by ozone, peracid, permanganate, hydroboration; of alcohols - by CrO3 based reagents, PCC; of aldehydes and ketones - by Ag+, permanganate, Jones’ reagent.
  • Reduction of alkenes and alkynes - by hydrogenation, metal/ammonia; of carbonyl compounds - by NaBH4 and LiAlH4.
  • Addition to carbonyl compounds - hydrates, hemiacetals, acetals, Schiff bases.
  • Substitution in acyl derivatives - interconversions of carboxylic acids, esters, amides, anhydrides and acid chlorides.

C-C Bond Formation:

  • Use of alkyllithiums, cuprates and Grignard reagents; use of cyanide and ethynide anions; use of enolates from aldehydes and ketones (aldol reactions), and from esters (Claisen ester condensation and use of ethyl acetoacetate).
  • Diels-Alder reaction as ring synthesis. Wittig reaction.

Examples of syntheses to illustrate these processes.

Chemistry of benzenoid aromatics:

Definition of ’aromaticity’ with reference to benzene. Simple orbital descriptions and the implications of these in terms of overall reactivity, both of the benzene ring itself and of a range of substituents.

Electrophilic substitution in benzene: basic mechanism (Wheland intermediates), evidence for this, common types of electrophile. Regioselectivity and reaction rates in electrophilic substitution of monosubstituted benzenes: principles, explanations, and extrapolations to polysubstituted benzenes. Interconversions of substituted benzenes, especially those involving anilines, phenols and halobenzenes.

Extension of principles of electrophilic substitution to naphthalene and anthracene.

Nucleophilic attack on benzenes: direct displacement, exemplified by Sanger’s reagent, and the benzyne mechanism; relationship to diazonium salt chemistry.

Summary of Hückel’s rule and the idea of anti-aromaticity: illustrations of this, including annulenes, charged ’aromatic’ species, azulenes and evidence for anti-aromaticity.

Practical work:

Preparative procedures - aromatic electrophilic bromination, oxidation of an alcohol, reduction of a ketone.

Separation of a mixture and identification of components

Thin-layer chromatography.