An Overview of Organic Reactions
Why this chapter?
Why this chapter?
To understand organic and/or biochemistry, it is
necessary to know:
-What occurs
-Why and how chemical reactions take place
We will see how a reaction can be described
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aoc i notes, Assignments of Organic Chemistry
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An Overview of Organic Reactions
Why this chapter? Why this chapter?
To understand organic and/or biochemistry, it is
necessary to know:
-What occurs
-Why and how chemical reactions take place
We will see how a reaction can be described
2
Kinds of Organic Reactions
(^) In general, we look at what occurs and try to learn how it happens (^) Common patterns describe the changes ◦ Addition reactions – two molecules combine ◦ Elimination reactions – one molecule splits into two
What kind of reaction is the transformation shown below?What kind of reaction is the transformation shown below?
- an elimination reaction
- a rearrangement reaction
- a substitution reaction
- an addition reaction
- none of these
+ HCl
Cl
Learning Check:
What kind of reaction is the transformation shown below?What kind of reaction is the transformation shown below?
- an elimination reaction
- a rearrangement reaction
- a substitution reaction
- an addition reaction
- none of these
+ HCl
Cl
Solution:
7
Steps in Mechanisms
We classify the types of steps in a sequence A step involves either the formation or breaking of a covalent bond Steps can occur in individually or in combination with other steps When several steps occur at the same time they are said to be concerted
8 Types of Steps in Reaction Mechanisms (^) Bond formation or breakage can be symmetrical or unsymetrical (^) Symmetrical- homolytic (^) Unsymmetrical- heterolytic Bond Breaking Bond Making Bond Making
10
Radical Reactions
(^) Not as common as polar reactions (^) Radicals react to complete electron octet of valence shell ◦ A radical can break a bond in another molecule and abstract a partner with an electron, giving substitution in the original molecule ◦ (^) A radical can add to an alkene to give a new radical, causing an addition reaction
11 (^) Three types of steps ◦ Initiation^ – homolytic formation of two reactive species with unpaired electrons Example – formation of Cl atoms form Cl 2 and light ◦ Propagation^ – reaction with molecule to generate radical (^) Example - reaction of chlorine atom with methane to give HCl and CH 3 .
Steps in Radical Substitution
13
Steps in Radical Substitution
Termination With excess concentration of Cl 2 present continued reaction is probable with formation of dichloro, trichloro, and tetrachloro methanes.
In a radical chain reaction, what would be the bestIn a radical chain reaction, what would be the best description of the following reaction? description of the following reaction? H H 33 C•C• ++ •Cl•Cl →→ CHCH 33 ClCl
- propagation
- elimination
- initiation
- termination
- substitution Learning Check:
16 Radical Substitution: With >1 kind of H When there is
- (^) >1 type of H then there is
- (^) >1 option for radical formation and therefore
- (^) >1 option for a monohalogenation product. C **H H H C C H H H H H C H H H C H H C Cl H H C H H H C Cl H C H H H
- Cl 2** hv (^) + 1-chloropropane (^) 2-chloropropane
In the reaction of ClIn the reaction of Cl 22 with 2-methylbutane, how manywith 2-methylbutane, how many monochlorinated monochlorinated isomers are produced?isomers are produced?
- 2
- 3
- 4
- 5
- 6 C H C C H H H H H C H H H C HH^ **H
- Cl 2** hv Learning Check:
19
Polar Reactions
Molecules can contain local unsymmetrical electron distributions due to differences in electro negativities This causes a partial negative charge on an atom and a compensating partial positive charge on an adjacent atom The more electronegative atom has the greater electron density Elements such as O, F, N, Cl more electronegative than carbon