Transcript Organic chemistry: introduction

During the reaction between chlorine and water, the
chlorine is both oxidized and reduced. Such a reaction in
which a substance is both oxidized and reduced is called a
(
).
(2)
(3)
(5)
(6)
(11)
(12)
(13)
(14)
potential energy
racemate
conjugate redox pair
sulfurous acid
吸热反应
偶极矩
化学平衡
反应机理
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Organic chemistry: introduction
Organic chemistry: introduction
A good organic answer:
makes a statement
gives an example or illustrates the statement
explains it using a theory or mechanism
It will be a factual statement about physical or chemical
properties which is explained by theories and mechanisms that
you have learnt in physical chemistry.
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Organic chemistry: introduction
e.g.
Facts
Theories
listed with an example
theories and ideas used
Physical properties such as:
state and fixed points
physical properties
solubility
explained in terms of
structure and bonding;
e.g. chain length
Chemical properties such as:
reactions with water,
acid, or base
explained in terms of
reactions with oxidizing
or reducing agents
explained in terms of
reactions with nucleophiles
and electrophiles
acid-base equilibria
redox equilibria
explained in terms of
functional group and its
reactive site and mechanism3
Organic chemistry: introduction
SOME IMPORTANT THEMES
Physical properties in similar compounds are controlled by chain
length.
The length of the chain controls the number of atoms and so the
number of electrons and so the strength of the van der Waals
forces between molecules.
Chemical properties are controlled by the kind of links
(functional groups ) in or joined to the chain: each functional
group has particular reactive sites.
Each reactive site gives the substance particular properties.
Two reactive sites next to each other modify each other.
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Organic chemistry: introduction
The type of carbon skeleton can change the properties of the
reactive site so compare:
Alkyl(烷基) chains and rings
acyl(酰基) chains
aryl(芳基) rings
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Organic chemistry: introduction
Words
Words and Expressions
organic chemistry
mechanism
reactive sites
functional group
theme
carbon skeleton
chain length
alkyl; alkyl chains and rings
acyl
aryl
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Functional groups and naming in organic compounds
Functional groups and naming in
organic compounds
The hydrocarbon part of an organic molecule is fairly unreactive,
so the chemistry of organic compounds is often dominated by
other atoms or groups of atoms joined to the chain. These atoms
or groups of atoms, whose reactions dominate the chemistry of
the molecule, are called functional groups.
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Functional groups and naming in organic compounds
NAMING ORGANIC COMPOUNDS
The name consists of three parts:
●the first part tells you the chain length
1 carbon = meth2 carbons = eth3 carbons = prop4 carbons = but●
5 carbons = pent6 carbons = hex7 carbons = hept8 carbons = oct-
nonadecaundecadodeca-
icosa-
the second part tells you about the linking or bonding in the chain
-an– means all single bonds in the carbon chain
-en- means a double bond in the carbon chain
-yn- means a triple bond in the chain
●
the last part tells you what functional group is joined to the chain
-e means only hydrogen is joined to the chain
-ol means an –OH; -amine means an –NH2
-al means a carbonyl group on the end of the chain
-one means a carbonyl group on the chain, but not at the end
-oic acid means a carboxylic group on the chain
Numbers are used to give the position along the chain.
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Functional groups and naming in organic compounds
Some common functional groups
Name of the group
Type of compound
Hydroxyl
Halogeno
Amino
Alcohol
Halide
Amine
Carbonyl
Formular or structure
-OH
-Hal
-NH2
Aldehyde
(at the end of the chain)
or ketone
(in the middle of the chain)
Carboxyl
Carboxylic acid
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Functional groups and naming in organic compounds
Examples
eth-an-al (acetaldehyde)
two carbons
single bond in the chain
carbonyl at the end of the chain
but-an-oic acid
four carbons
single bonds in the chain
carboxylic acid at the end
prop-2-en-1-ol
three carbons
double bond in the chain
hydroxyl group at the end
pent-an-2-one
five carbons
single bonds in the chain
carbonyl on the second carbon
(the dashes between the separate parts of the name are left out unless numbers10
are needed)
Functional groups and naming in organic compounds
Words
Words and Expressions
carbonyl group
carboxylic group
alcohol
aldehyde
ketone
carboxylic acid
amine
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Bonding and structure in organic compounds
Bonding and structure in organic compounds
Carbon forms a huge number of compounds:
About 20 times more than all the other elements put together.
The study of this great number of compounds all based on
carbon is called organic chemistry.
There are a number of special reasons for this behavior of
carbon:
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Bonding and structure in organic compounds
1. BONDING
Carbon-carbon bonds are much stronger than the bonds between
atoms of most other elements.
The bonds between carbon and hydrogen are also relatively
strong.
Bond
C-C
Bond energy kJ mol-1
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O-O
N-N
S-S
144
158
266
C-H
413
C-O
C-N
358
286
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Bonding and structure in organic compounds
2. QUADRA- OR TETRA-VALENCY
Carbon is in group 4 and forms four bonds.
The ability to form four strong bonds results in atoms arranged
in chains (both straight and branched) and in rings.
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Bonding and structure in organic compounds
3. SIMILAR ELECTRONEGATIVITY OF CARBON AND
HYDROGEN
There is very little charge separation along a carbon-hydrogen
bond:
So the hydrocarbon part of the molecule is unreactive and very
stable.
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Bonding and structure in organic compounds
The shape of molecules with many atoms in is complicated and
there are several ways of drawing them:
Flat or planar structure
Three dimensional structure showing the
arrangements of bonds around the carbon atoms
tetrahedral
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Bonding and structure in organic compounds
Words
Words and Expressions
Straight chain; branched chain
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Key ideas in organic chemistry
Key ideas in organic chemistry
REACTIVE SITES
Do the atoms differ in electronegativity? If so there will be charge
separation.
Is there a double bond? If so there will be a pi system.
Do any of the atoms have lone pairs?
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Key ideas in organic chemistry
WHAT ATTACKS WHAT?
Nucleophiles will attack electron deficient regions.
Electrophiles will attack electron rich regions.
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Key ideas in organic chemistry
WILL THE REACTION WORK?
How good is the nucleophile or electrophile?
Good bases are usually good nucleophiles
How reactive is the site?
Can the attacking particle get in? is there steric hindrance?
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Key ideas in organic chemistry
How strong are the bonds? Will they break easily?
How stable is the leaving group? Weak bases are good leaving
groups.
A leaving group is an atom or group of atoms which leaves a
molecule to make way for an incoming group.
H2O is a better leaving group than OH21
Key ideas in organic chemistry
MECHANISM
What is the best alignment or orientation of the particles?
What are the electron rearrangements?
How stable is the intermediate?
Will the activation energy be high or low?
Will the reaction be slow or fast?
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Key ideas in organic chemistry
Words
Words and Expressions
reactive sites
attack
electron deficient; electron rich
steric hindrance; hinder
leaving group
alignment
orientation
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Reactive sites and organic reagents
Reactive sites and organic reagents
FUNCTIONAL GROUPS AND REACTIVE SITES
Functional groups control the chemistry of molecules because they
contain reactive sites.
There are two kinds of reactive site in a molecule.
Electron deficient sites (shown by the d+ sign) are short of electrons.
Electron excessive sites (shown by the d– sign ) are rich in electrons.
Electron deficient sites
an atom bonded to a more
electronegative one
positive ions
Electron excessive sites
an atom with lone pair(s)
a pi system
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Reactive sites and organic reagents
REAGENTS
Reagents are substances that are added to organic compounds to
make them react. Typical reagents are bromine water and
sodium hydroxide.
Reagents are classified by the kind of reactive site they react with.
Reagents that are attracted to regions of positive charge or
electron deficient sites are called nucleophiles. Nucleophiles are
particles with lone pairs of electrons.
A useful general rule is that good bases are usually good
nucleophiles
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Reactive sites and organic reagents
Reagents that are attracted to regions of negative charge or
electron excessive sites are called electrophiles. Sometimes a
dipole is induced or caused by the compound it is reacting with,
making an electrophile. So an electrophile is an electron pair
acceptor.
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Reactive sites and organic reagents
CLASSIFYING ORGANIC REACTIONS
Organic reactions are classified in two ways:
1. By the type of reagent being used. If a nucleophile is being
added the reaction is called nucleophilic; if an electrophile is
added it is called electrophilic.
2. By what happens when the reaction is over. If an atom or group
has been added the reaction is called an addition, or the opposite
might happen and atoms from two neighboring carbons are lost,
when the reaction is called an elimination. If one atom or group
is replaced by another, the reaction will be called a substitution.
In a substitution, the atom or group being replaced is called the
leaving group. Particles which leave easily are called good leaving
groups. Usually weak bases (bad nucleophiles) are good leaving
groups.
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Reactive sites and organic reagents
CLASSIFYING ORGANIC REACTIONS
On the next pages you will see examples of:
Nucleophilic substitution
Electrophilic substitution
Nucleophilic addition
Electrophilic addition
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Reactive sites and organic reagents
REACTION MECHANISMS
During any reaction, bonds are broken and made. As bonds are
attractive forces between positive and negative bits of particles,
making and breaking them means moving electrons around.
A mechanism is a description of a successful collision between the
reactants (a reagent particle and the organic compound particle)
and the electron rearrangements that happen as reactants are
changed into products.
Most mechanisms are a series of three labeled diagrams showing
the particles:
● just before a successful collision and therefore lined up properly
● during the collision as the electrons are moving
● and after the collision.
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Reactive sites and organic reagents
Words
Words and Expressions
electron deficient sites; electron excessive sites
addition
elimination; eliminate
substitution; substitute, replace
leaving group
nucleophilic substitution; electrophilic substitution;
nucleophilic addition; electrophilic addition
collision; collide
line up
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Drawing mechanism
Drawing mechanisms
ELECTRON REARRANGEMENTS AND CURLY ARROWS
During a reaction bonds are broken and made.
Bonds consist of electrons and so during a reaction, electrons are
moving.
Electrons in the outer shell have to be:
Sigma pairs
between a pair of atoms
pi pairs
between a pair of atoms
lone pairs
on a single atom
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Drawing mechanism
During the reaction the pairs of electrons change from one kind of
pair to another: for example
a sigma pair changes into a lone pair
a pi pair changes into a lone pair
a lone pair changes into a pi pair
These electron movements are shown by curly arrows which start on
the original electron pair and end where the electrons have gone.
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Drawing mechanism
A simple acid—base reaction
H2O + HCl → H3O+ + Cl-
For the reaction to happen, a new bond must be made between
the oxygen of the water molecule and the hydrogen atom of the
hydrogen chloride. Also the bond between the hydrogen and the
chlorine atom must break. These changes can be shown by curly
arrows:
Here a lone pair has become a sigma pair and a sigma pair has
become a lone pair.
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Drawing mechanism
The bond between the hydrogen and chlorine has broken
unevenly, with both the electrons ending up on the chlorine. This
is an example of heterolysis.
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Drawing mechanism
Fish hooks and free radicals
A free radical forms when a covalent bond breaks in half evenly,
one electron going to each atom. This kind of bond cleavage or
breakage is called homolysis. The movement of the single
electrons is shown by an arrow with half a head. This looks like,
and is called, a fish-hook.
The particles formed have a single unpaired electron and are
called free radicals.
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Drawing mechanism
DRAWING MECHANISMS
When you are drawing the three stages of a mechanism, you must think of
and comment on different things.
Stage 1: Here the most important thing to think about is getting the two
particles lined up properly so that the oppositely charged bits are next to
each other. In your labeling, you should try to explain why each bit has the
charge you have shown.
Stage 2: in this part, you will be thinking about how strong the bonds are
that might break and where the electrons are going if the bond does break.
Is the particle being attacked saturated or not? If it is saturated, there is not
much room for the incoming electrons and the reaction will have a high
activation energy. This means it will go slowly. If the particle being
attacked is unsaturated, then p electrons can be moved out of the way
easily, becoming lone pairs or s pairs and so the reaction will have a low
activation energy and go quite quickly.
Stage 3: Here you think about the energy or stability of what you have
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made. Is the leaving group stable?
Drawing mechanism
Words
Words and Expressions
rearrangement
curly arrow
unevenly; evenly
heterolysis; heterolytic cleavage
homolysis; homolytic cleavage
fish hook
free radical
saturated; unsaturated
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