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 !!