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Mòdul MD2301 - Formació general; 564497 – Química orgànica i inorgànica
MASTER ON DRUGS, COSMETICS AND FOOD QUALITYMASTER ON DRUGS, COSMETICS AND FOOD QUALITY
Dr. Antonio DelgadoUniversitat de BarcelonaOctober 2009
2
Structure of organic compounds
Chemical bond; hybridization; resonance and aromaticity
Stereochemistry Conformational analysis of alkanes and cycloalkanes; chirality; stereochemical descriptors
Organic reactivity Functional groups; C-C bond forming reactions; Functional group transformations
Thematic bloc: Organic chemistry
3
Session 1
Basic principles of chemical reactions: Kinetic and thermodynamic processes. Concerted and stepwise processes. Reaction intermediates: radicals and ions (homolytic and hereterolytic bond-breaking processes). Types of organic chemical reactions: substitution, elimination, addition, addition-elimination, oxidation, reduction.
Substitution reactions at saturated carbons. Nucleophiles and Electrophiles. Nucleophilic substitution reactions. Alkyl halides as electrophiles. Concerted (SN2) versus stepwise (SN1) processes. Other electrophiles and nucleophiles. Synthetic applications.
Elimination reactions. Concerted (E2) versus stepwise (E1) mechanisms. Mechanistic considerations. Competition between SN and E processes. Synthetic applications of the elimination reactions.
4
“Communication in Chemistry”
Atoms are the alpahabet of chemistryMolecules are the words
Reaction mechanisms are the grammar Synthetic sequences are the sentences
5
Kinetics and thermodynamics of chemical reactions
6
Kinetic versus thermodynamic control
7
Concerted mechanism Stepwise mechanism
Reaction mechanisms(Nucleophilic substitution in alkyl halides)
8
Stepwise (non-concerted) mechanismsTake place through reaction intermediates
(species that can be detected or isolated)
Radical Species with an unpaired electronFormed by the homolytic breakage of a chemical bond
IonCharged speciesFormed by the heterolytic breakage of a chemical bond
9
Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction(s) regardless of the size of the molecule it is a part of. However, its relative reactivity can be modified by nearby functional groups.
10
We say that the carbon atoms carrying functional groups that can be interconverted without the need for reducing agents (or oxidizing agents) have the same oxidation level
11
Types of organic chemical reactions
• Substitution
• Elimination
• Addition
• Oxidations
• Reductions
A B A C
C
B
A B A B
DH
D
H
A BA BE
D-ED
R H
O
R OH
O
C NR R-CH2NH2
12
Nucleophile: Neutral or charged reagent that forms a chemical bond to its reaction partner (the electrophile) by donating both bonding electrons.
AnionsNeutral species with a non-bonding electron pairs.
Electrophile: Reagent that participates in a chemical reaction by accepting an electron pair (from the nucleophile) in order to form a chemical bond
CationsNeutral species with polarized bonds.
Nucleophilicity and electrophilicity are kinetic terms
Substitution reaction at saturated carbonsNucleophilic substitution (SN)
Some basic concepts
13
Properties of the C-X bond
Alkyl halides are electrophiles
14Concerted versus stepwise mechanism
15
SN1 Reaction
Stepwise mechanism/Planar intermediate/Racemization !!
Reaction intermediate
16
SN2 Reaction
Concerted mechanism/Dorsal attack/Stereochemical control !!
17
18
19
Synthetic applications: alkenes
20
Stepwise elimination (E1)
Carbocationic intermediate
21
Competition SN1/E1 are due to the fact that nucleophiles are also bases !! (dual character)
22
Stereochemical control !!
23
24
SN2 and E2 are also competing processes !!
25
All 4 processes (SN1, SN2, E1, E2) can compete !! However……
Not synthetically usefulSynthetically useful !!