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Transcript
Introduction (HL)
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Amines are derivatives of ammonia, where 1, 2 or 3
hydrogens have been displaced by carbon chains.
Amines are therefore classified as primary, secondary or
tertiary.
Nucleophilic substitution reactions
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http://www.youtube.com/watch?v=h5xvaP6bIZI
http://www.youtube.com/watch?v=JmcVgE2W
KBE
Factors affecting the rate:
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a)
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b)
c)
Tertiary
halogenoalkanes
>
secondary
halogenoalkanes
>
primary
halogenoalkanes
halogenoalkane + water/OH- → alcohol
dilute sodium hydroxide solution
halogenoalkane + ammonia → amine
halogenoalkane + cyanide → nitrile
nitrile → amine
nitrile → carboxylic acid
Elimination reactions
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Removal of a small molecule from a larger molecule.
A halogenoalkane reacts with a hot solution of NaOH dissolved in
ethanol to produce an alkene.
The hydroxide ion acts as a Bronstedt-Lowry base and accepts a
proton.
NOTE! Under different conditions halogenoalkanes react with OH - to
form alcohols (substitution)!
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Therefore, altering the reaction conditions can give completely different
products from the same reactants.
Condensation reactions
Two molecules react together to produce a
larger molecule and a small by-product (often water).
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carboxylic acid + alcohol → ester
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Esters have distinctive smells (often fruity and sweet)
and they are used in:
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Perfumes
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Artificial food flavourings
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Painkillers
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Solvents for paints
carboxylic acid + amine → amide
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The bond is called a peptide bond and the product is
called a dipeptide.
Condensation polymerization
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The condensation can continue to form a polymer if
each of the reacting monomer contains TWO
functional groups that can undergo condensation.
Polyesters
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Polyesters are made by condensing diols
with dicarboxylic acids.
Polyamides
Demo: Synthesis of nylon
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Solution A: 0,5 g 1,6-diaminohexane
0,5 g sodiumcarbonate
25 ml water
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Solution B: 1 ml sebacoyl chloride
30 ml hexane
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Slowly pour the solution B into the solution A.
Proteins (natural polyamides)
Reaction pathways
http://www.youtube.com/watch?v=41n3mDoVbvk
Stereoisomerism
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Structural isomers have the same molecular formula
but a different structural formula.
Stereoisomers have the same structural formula but
have the atoms arranged differently in space.
There are two types of stereoisomerism: geometrical
and optical isomerism.
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http://www.youtube.com/watch?v=RBtgAz70_J
Y
Geometrical isomerism
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Geometrical isomerism occurs with restricted rotation,
i.e. when bonds are unable to rotate freely.
Double bond: the pi-bond prevents rotation.
Cycloalkanes: rotation is restricted due to the
ring structure
Physical and chemical properties of cis- and trans
isomers are often different, although there does not tend
to be a general pattern that applies to all types of
compounds.
Optical isomerism
lemon
orange
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Optical isomerism is shown by all compounds that
contain at least one asymmetric carbon atom within
the molecule.
Chiral molecules are molecules that contain an
asymmetric carbon atom.
A carbon atom is asymmetric (=chiral) if it has four
different atoms or groups bonded to it.
Enantiomers
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The two mirror images, i.e. isomers, are called
enantiomers.
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Enantiomers have similar chemical properties, unless
they react with other optically active substances (as in
the human body, where their physiological effects
differ).
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Enantiomers differ in only one aspect of their physical
properties: they rotate the plane of plane-polarized
light in opposite directions:
- laevorotatory enantiomers counterclockwise (to the left)
- dextrorotatory clockwise (to the right)
Polarimeter
Racemic mixture
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If both enantiomers are equally present, it is called a
racemic mixture or racemate.
The two enantiomers rotate the plane of the polarized
light by the same amount but in opposite directions.
The rotations cancel each other out and the mixture
appears to be optically inactive.