Post on 22-Dec-2015
transcript
MUDDLE YOUR WAY MUDDLE YOUR WAY THROUGH ORGANIC THROUGH ORGANIC
MECHANISMSMECHANISMS
KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING
A A VERYVERY BRIEF INTRODUCTION BRIEF INTRODUCTION
2008 2008 SPECIFICATIONSSPECIFICATIONS
INTRODUCTION
This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards.
Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available.
Accompanying notes on this, and a full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at...
www.knockhardy.org.uk/sci.htm
Navigation is achieved by...
either clicking any grey arrows at the foot of each page
or using the left and right arrow keys on the keyboard
KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING
MUDDLE YOUR WAY THROUGH MECHANISMSMUDDLE YOUR WAY THROUGH MECHANISMS
MEET THE ATTACKERSMEET THE ATTACKERS
I AM A NUCLEOPHILE
I HAVE A LONE PAIR WHICH I CAN USE TO FORM A NEW BOND.
I ATTACK ELECTRON DEFICIENT AREAS (those with a + or )
MEET THE ATTACKERSMEET THE ATTACKERS
I AM AN ELECTROPHILE
I HAVE A + CHARGE or a CHARGE. I ATTACK ELECTRON
RICH AREAS SUCH AS C=C DOUBLE BONDS.
MEET THE ATTACKERSMEET THE ATTACKERS
AND I AM A FREE RADICAL
I HAVE AN UNPAIRED ELECTRON WHICH I WANT TO PAIR UP. I AM
VERY REACTIVE AND DON’T MIND WHERE I ATTACK… WATCH OUT!
THE BONDING IN A MOLECULEINFLUENCES WHAT WILL ATTACK IT
SINGLEA typical covalent bond with one shared pair – nothing to tempt an attacking species
WHO IS ATTACKED?WHO IS ATTACKED?
THE BONDING IN A MOLECULEINFLUENCES WHAT WILL ATTACK IT
SINGLE
MULTIPLE
A typical covalent bond with one shared pair – nothing to tempt an attacking species
Bond has twice as many electrons – species which like electrons will be attracted
WHO IS ATTACKED?WHO IS ATTACKED?
THE BONDING IN A MOLECULEINFLUENCES WHAT WILL ATTACK IT
SINGLE
MULTIPLE
NON-POLAR
A typical covalent bond with one shared pair – nothing to tempt an attacking species
Bond has twice as many electrons – species which like electrons will be attracted
Similar atoms have an equal attraction for the shared pair of the covalent bond
WHO IS ATTACKED?WHO IS ATTACKED?
THE BONDING IN A MOLECULEINFLUENCES WHAT WILL ATTACK IT
SINGLE
MULTIPLE
NON-POLAR
POLAR
A typical covalent bond with one shared pair – nothing to tempt an attacking species
Bond has twice as many electrons – species which like electrons will be attracted
Similar atoms have an equal attraction for the shared pair of the covalent bond
Atoms have different electronegativities and the shared pair will be attracted more to one end – species known as nucleophiles will be attracted to the slightly positive end
WHO IS ATTACKED?WHO IS ATTACKED?
THE BONDING IN A MOLECULEINFLUENCES WHAT WILL ATTACK IT
SINGLE
MULTIPLE
NON-POLAR
POLAR
A typical covalent bond with one shared pair – nothing to tempt an attacking species
Bond has twice as many electrons – species which like electrons will be attracted
Similar atoms have an equal attraction for the shared pair of the covalent bond
Atoms have different electronegativities and the shared pair will be attracted more to one end – species known as nucleophiles will be attracted to the slightly positive end
WHO IS ATTACKED?WHO IS ATTACKED?
ALKANES ARE RELATIVELY UNREACTIVE ORGANIC COMPOUNDS
ALKANES CONTAIN TWO BOND TYPES
C-H and C-C
WHAT ATTACKS ALKANES?WHAT ATTACKS ALKANES?
Both bonds are single – no electron rich areas
Bonds are non-polar - no electron deficient areas
Free radicals are very reactive and do attack
FREE RADICAL SUBSTITUTIONFREE RADICAL SUBSTITUTION
ALKENES ARE MUCH MORE REACTIVE THAN ALKANES
ALKENES CONTAIN A C=C BONDThere will be twice as many electrons between the carbon atoms as there are in a single bond
WHAT ATTACKS ALKENES?WHAT ATTACKS ALKENES?
C=C bond is double – an electron rich area
Bonds are non-polar - no electron deficient areas
ELECTROPHILIC ADDITIONELECTROPHILIC ADDITION
HALOGENOALKANES ARE MUCH MORE REACTIVE THAN ALKANES
HALOGENOALKANES CONTAIN A POLAR BONDThe halogen is more electronegative than the carbon attracts the shared electron pair.
WHAT ATTACKS HALOGENOALKENES?WHAT ATTACKS HALOGENOALKENES?
Bond is single – not an electron rich area
Bond is polar – the greater electronegativity of the halogen creates a dipole making the carbon atom electron deficient.
NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION
THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS
CURLY ARROWSCURLY ARROWS
ELECTRONS MOVE FROM AREAS OF HIGH ELECTRON DENSITY TO ONES WITH A LOWER ELECTRON DENSITY
THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS
CURLY ARROWSCURLY ARROWS
ELECTRONS MOVE FROM AREAS OF HIGH ELECTRON DENSITY TO ONES WITH A LOWER ELECTRON DENSITY
For example…from LONE PAIRS
DOUBLE BONDS
THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS
CURLY ARROWSCURLY ARROWS
ELECTRONS MOVE FROM AREAS OF HIGH ELECTRON DENSITY TO ONES WITH A LOWER ELECTRON DENSITY
For example…from LONE PAIRS
DOUBLE BONDS
to POSITIVE SPECIESTHE END OF POLAR BONDS
THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS
ARROWS WITH TWO ‘HEADS’ INDICATE THE MOVEMENT OF TWO (A PAIR OF) ELECTRONS
CURLY ARROWSCURLY ARROWS
THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS
ARROWS WITH TWO ‘HEADS’ INDICATE THE MOVEMENT OF TWO (A PAIR OF) ELECTRONS
CURLY ARROWSCURLY ARROWS
A PAIR of electrons moves from here… to here
THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS
ARROWS WITH TWO ‘HEADS’ INDICATE THE MOVEMENT OF TWO (A PAIR OF) ELECTRONS
CURLY ARROWSCURLY ARROWS
A PAIR of electrons moves from here… to here
ARROWS WITH ONE ‘HEAD’ INDICATE THE MOVEMENT OF JUST ONE ELECTRON
THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS
ARROWS WITH TWO ‘HEADS’ INDICATE THE MOVEMENT OF TWO (A PAIR OF) ELECTRONS
CURLY ARROWSCURLY ARROWS
A PAIR of electrons moves from here… to here
ARROWS WITH ONE ‘HEAD’ INDICATE THE MOVEMENT OF JUST ONE ELECTRON
ONE electron moves from here… to here
THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS
ARROWS WITH TWO ‘HEADS’ INDICATE THE MOVEMENT OF TWO (A PAIR OF) ELECTRONS
CURLY ARROWSCURLY ARROWS
A PAIR of electrons moves from here… to here
ALWAYS BE PRECISE WITH THE POSITIONING OF ANY ARROWSALWAYS BE PRECISE WITH THE POSITIONING OF ANY ARROWS
ARROWS WITH ONE ‘HEAD’ INDICATE THE MOVEMENT OF JUST ONE ELECTRON
ONE electron moves from here… to here
NUCLEOPHILES:- possess a lone pair of electrons
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
HYDROXIDE ION
negative charge
H Olone pair
more lone pairs
NUCLEOPHILES:- possess a lone pair of electrons
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
HYDROXIDE ION
negative charge
H Olone pair
more lone pairs
AMMONIA MOLECULE
Nucleophiles don’t need to have negative charge… BUT they must have a lone pair
lone pair
H
H N
H
NUCLEOPHILES:- possess a lone pair of electrons
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
HYDROXIDE ION
negative charge
H Olone pair
more lone pairs
AMMONIA MOLECULE
Nucleophiles don’t need to have negative charge… BUT they must have a lone pair
lone pair
H
H N
H
ELECTROPHILES:- attract a lone pair of electrons
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
HYDROGEN ION HThere are no electrons in the outer shell of hydrogen so it has space to accept two electrons
ELECTROPHILES:- attract a lone pair of electrons
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
HYDROGEN ION HThere are no electrons in the outer shell of hydrogen so it has space to accept two electrons
HYDROGEN CHLORIDE
contains a POLAR BOND; the end will attract the electron pair H Cl
ELECTROPHILES:- attract a lone pair of electrons
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
HYDROGEN ION HThere are no electrons in the outer shell of hydrogen so it has space to accept two electrons
HYDROGEN CHLORIDE
contains a POLAR BOND; the end will attract the electron pair H Cl
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
‘BALANCING THE BOOKS’
H O H C C Br
H
3
H
H C C O H
H
3
H
Br
This is the basic mechanism for the nucleophilic substitution of bromoethane.
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
‘BALANCING THE BOOKS’
H O H C C Br
H
3
H
H C C O H
H
3
H
Br
This is the basic mechanism for the nucleophilic substitution of bromoethane. To see how it works, it helps to show the electrons involved.
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
‘BALANCING THE BOOKS’
H O H C C Br
H
3
H
H C C O H
H
3
H
Br
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
‘BALANCING THE BOOKS’
H O
The hydroxide ion has a – ive charge, The oxygen has eight electrons in its outer shell. Because it has a lone pair, the ion will act as a nucleophile
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
‘BALANCING THE BOOKS’
H O H C C Br
H
3
HIn bromoethane, C2H5Br, the C-Br bond is polar because the electronegativity of Br is greater than C. It will susceptible to attack by nucleophiles.
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
‘BALANCING THE BOOKS’
H O H C C Br
H
3
HA pair of electrons moves from th hydroxide ion to the slightly positive carbon in bromoethane.
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
‘BALANCING THE BOOKS’
H O H C C Br
H
3
HCarbon has a full outer shell of eight electrons so as two come in, two must leave.
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
‘BALANCING THE BOOKS’
H O H C C Br
H
3
HThe C-Br bond breaks as the shared pair of electrons move onto the bromine.
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
‘BALANCING THE BOOKS’
H O H C C Br
H
3
H
H C C O H
H
3
H
Br
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
‘BALANCING THE BOOKS’
H O H C C Br
H
3
H
H C C O H
H
3
H
Br
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
‘BALANCING THE BOOKS’
H O H C C Br
H
3
H
H C C O H
H
3
H
Br
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
more lone pairs‘BALANCING THE BOOKS’
H O H C C Br
H
3
H
H C C O H
H
3
H
Br
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
more lone pairs‘BALANCING THE BOOKS’
H O H C C Br
H
3
H
H C C O H
H
3
H
Br
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
more lone pairs‘BALANCING THE BOOKS’
H O H C C Br
H
3
H
H C C O H
H
3
H
Br
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION
negative charge
H O
lone pair
more lone pairs
‘BALANCING THE BOOKS’
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
more lone pairs‘BALANCING THE BOOKS’
H O H C C Br
H
3
H
H C C O H
H
3
H
Br
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
negative charge
lone pairmore lone pairs
‘BALANCING THE BOOKS’
H O H C C Br
H
3
H
H C C O H
H
3
H
Br
DRAWING CURLY ARROWSDRAWING CURLY ARROWS
When moving electrons about, it is essential to check that the charges on the reactants and products balance.
NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION
negative charge
H O
lone pair
more lone pairs
‘BALANCING THE BOOKS’