Reaction Classes and Pericyclic Reactions
CEM 3005W 2013
“Reaction Classes and Pericyclic Reactions”
● 4 Lectures
● Recommended Texts: (i) J. March “Advanced Organic Chemistry”, p 839, `---Edn., Oxford (W); Warren (2) Ch 34, 35.
Syllabus
1) General principles
(a) Reaction classes
(i) Heterolytic
(ii) Homolytic (iii) Pericyclic
(b) Pericyclic Reaction Types
2) Electrocyclic Reactions
(a) Definition and examples
(b) Stereochemical aspects and the Woodward and Hoffmann rules
3) Cycloaddition Reactions (a) Definition and examples (b) Stereochemical aspects and the Woodward and Hoffmann rules (c) The Diels-Alder reaction (i) Stereospecific syn-addition (ii) Diene conformation (iii) Exo/endo stereoselectivity
4) Sigmatropic Rearrangements (a) Definition, examples and numbering NOTES
1) General Principles – Book reading is highly recommended for this topic
(a) Reaction classes
Only three reaction classes occur in (organic) chemistry, defined as:
(i) Heterolytic – here one partner donates or departs with both electrons while the other (partner) supplies a vacant orbital. The reaction-energy diagram (profile) tends to have at least one intermediate. These reactions involve a “two-electron push”:
Examples:
(ii) Homolytic – here each partner supplies one electron as a radical (a species with a single unpaired electron). These reactions involve a single-electron push – see W (2) Ch 37 on Radical reactions:
Examples – the SET reaction in the Grignard practical as well as the classical free-radical chlorination of a hydrocarbon like cyclohexane, which typically illustrates the free-radical mechanism (see side-chain functionalisation in Aromatic notes with NBS), in which there are initiation, propagation and termination steps:
(iii) Pericyclic – in a class of its own! By definition, a concerted (pericyclic) process is one in which electrons move in
“Reaction Classes and Pericyclic Reactions”
● 4 Lectures
● Recommended Texts: (i) J. March “Advanced Organic Chemistry”, p 839, `---Edn., Oxford (W); Warren (2) Ch 34, 35.
Syllabus
1) General principles
(a) Reaction classes
(i) Heterolytic
(ii) Homolytic (iii) Pericyclic
(b) Pericyclic Reaction Types
2) Electrocyclic Reactions
(a) Definition and examples
(b) Stereochemical aspects and the Woodward and Hoffmann rules
3) Cycloaddition Reactions (a) Definition and examples (b) Stereochemical aspects and the Woodward and Hoffmann rules (c) The Diels-Alder reaction (i) Stereospecific syn-addition (ii) Diene conformation (iii) Exo/endo stereoselectivity
4) Sigmatropic Rearrangements (a) Definition, examples and numbering NOTES
1) General Principles – Book reading is highly recommended for this topic
(a) Reaction classes
Only three reaction classes occur in (organic) chemistry, defined as:
(i) Heterolytic – here one partner donates or departs with both electrons while the other (partner) supplies a vacant orbital. The reaction-energy diagram (profile) tends to have at least one intermediate. These reactions involve a “two-electron push”:
Examples:
(ii) Homolytic – here each partner supplies one electron as a radical (a species with a single unpaired electron). These reactions involve a single-electron push – see W (2) Ch 37 on Radical reactions:
Examples – the SET reaction in the Grignard practical as well as the classical free-radical chlorination of a hydrocarbon like cyclohexane, which typically illustrates the free-radical mechanism (see side-chain functionalisation in Aromatic notes with NBS), in which there are initiation, propagation and termination steps:
(iii) Pericyclic – in a class of its own! By definition, a concerted (pericyclic) process is one in which electrons move in