2021/22 Undergraduate Module Catalogue

CHEM2121 Organic Chemistry: Conformation, Configuration & Reactivity

10 creditsClass Size: 140

Module manager: Prof Steve Marsden
Email: s.p.marsden@leeds.ac.uk

Taught: Semester 1 (Sep to Jan) View Timetable

Year running 2021/22

Pre-requisite qualifications

Level 1 Chemistry or equivalent

Module replaces

CHEM2141 Introduction to Organic Synthesis

This module is not approved as a discovery module

Module summary

This module will examine how the shapes of organic molecules impact their physical properties and reactivity. This will encompass both the relative and absolute arrangement of the atoms defined by bonding (configuration) as well as the shapes that molecules adopt by rotation/torsion about bonds (conformation).It will also introduce enols/enolates as reactive carbon-centred nucleophiles for the formation of carbon-heteroatom and carbon-carbon bonds, and their applications in the synthesis of complex organic molecules.

Objectives

- To understand the meaning and significance of conformation and configuration of organic compounds, and their influence on organic structure/reactivity (stereoelectronic effects);
- To introduce the physical organic concepts that allow the outcome of organic reactions to be rationalised and understood;
- Knowledge of key reactions in organic chemistry including substitution reactions of heterocycles, reactions involving enols and enolates.

Learning outcomes
Students will be able to:
1. draw appropriate representations of the conformations of cyclic and acyclic molecules and rationalise the relative energies of these in terms of favourable/unfavourable interactions;
2. rationalise the stereochemical and/or regiochemical outcome of reactions (e.g. substitution, elimination, ring-opening, rearrangement) by considering the spatial arrangement of relevant orbitals (stereoelectronics);
3. recognise, identify and correctly label different stereoisomeric molecules (enantiomers, diastereomers);
4. rationalise the relative rates of ring-closure of acyclic molecules in terms of balancing enthalpic and entropic contributions;
5. identify and/or draw enol/enolate forms of carbonyl compounds and to predict equilibrium concentrations of enolates from pKa data;
6. write appropriate mechanisms for the reactions of enols and enolates with appropriate electrophiles and rationalise the outcome of the reactions in terms of kinetic and thermodynamic parameters;
7. rationalise the stereochemical outcome of enolate formation and aldol reactions in terms of well-defined six-membered transition state diagrams.

Skills outcomes
Students will gain skills in: identification and characterisation of stereoisomeric molecules; understanding and predicting the three-dimensional shape of simple organic molecules; rationalising and predicting reaction outcomes through consideration of the spatial arrangement of reacting orbitals; identifying appropriate conditions for the generation of enols or enolates as reactive carbon-centred nucleophiles for organic synthesis; predicting and rationalising the outcome of chemical reactions of enols/enolates with heteroatom- and carbon-centred electrophiles.

Syllabus

STEREOCHEMISTRY AND CONFORMATIONAL ANALYSIS
The difference between conformation and configuration.

Conformation: Newman projections. Torsional strain. Angle strain and transannular strain in small and medium rings. Chair conformations of 6-rings. 1,3-Diaxial interactions to determine conformation. Conformational analysis of cyclohexenes and cyclohexanonones. Use of NMR in determining favoured conformations. Entropic and enthalpic contributions in thermodynamic control of ring size and (kinetic) ring formation.

Stereochemistry: Enantiomers are non-superimposable mirror image compounds. Types of chirality: stereogenic centres, axial chirality (allenes; biaryl compounds – atropisomers), planar chirality .The difference between enantiomers and diastereoisomers. Alkene geometry. Homotopic, enantiotopic and diastereotopic groups - the substitution test. Diastereotopic groups can be distinguished in NMR spectra.

STEREOELECTRONIC EFFECTS
Revision of SN2 in terms of sigma orbital - the overlap of filled and empty orbitals. Sigma orbitals in other reactions in which a bond is broken; E2. Use of Newman projections. The anomeric effect: kinetic and thermodynamic aspects. Epoxides and iodonium ions etc. have similar conformations to the parent alkenes. Transdiaxial opening of epoxides, iodonium ions etc; iodolactonisation. Suprafacial rearrangements (retention of configuration at the migratory origin, discussion in terms of orbitals). The Wittig reaction: explanation of the stereochemical aspects using Newman projections.

ENOLS AND ENOLATES
Introduction to enols and enolates. Enolisation under base and acidic conditions. Enolate formation; revision of pKa and choice of base. Kinetic and thermodynamic enolate formation. Introduction to enamines. Reactions of enols and enolates: bromination, alkylation, aldol reaction (inter- and intramolecular), Mannich reaction, Claisen condensation/Dieckmann cyclisation, Michael additions. Introduction to six-membered transition states (Zimmerman-Traxler model and enolate formation); diastereomeric enolates give diastereomeric aldol adducts.

Teaching methods

Delivery type	Number	Length hours	Student hours
Workshop	8	1.00	8.00
e-Lecture	1	1.00	1.00
Seminars	2	1.00	2.00
Tutorial	2	1.00	2.00
Independent online learning hours			87.00
Private study hours			0.00
Total Contact hours			13.00
Total hours (100hr per 10 credits)			100.00

Private study

Working though online material, background reading and preparing for workshops (44h)
Working through formative problems including online learning (14h);
Preparation for tutorials (6h);
Preparation for exam (23h).

Opportunities for Formative Feedback

Short online MCQs. Online workshops with in-class feedback'

Methods of assessment

Exams

Exam type	Exam duration	% of formal assessment
Open Book exam	2 hr	100.00
Total percentage (Assessment Exams)		100.00

Normally resits will be assessed by the same methodology as the first attempt, unless otherwise stated

Reading list

The reading list is available from the Library website

Last updated: 02/07/2021 10:55:13

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