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MUDDLE YOUR WAY THROUGH ORGANIC MECHANISMS

MUDDLE YOUR WAY THROUGH ORGANIC MECHANISMS. A VERY BRIEF INTRODUCTION. 2008 SPECIFICATIONS. KNOCKHARDY PUBLISHING. KNOCKHARDY PUBLISHING. MUDDLE YOUR WAY THROUGH MECHANISMS. INTRODUCTION

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MUDDLE YOUR WAY THROUGH ORGANIC MECHANISMS

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  1. MUDDLE YOUR WAY THROUGH ORGANIC MECHANISMS A VERY BRIEF INTRODUCTION 2008 SPECIFICATIONS KNOCKHARDY PUBLISHING

  2. KNOCKHARDY PUBLISHING MUDDLE YOUR WAY THROUGH MECHANISMS 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

  3. MEET THE ATTACKERS Press the space bar

  4. MEET 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 + ord+)

  5. MEET THE ATTACKERS Press the space bar

  6. MEET THE ATTACKERS I AM AN ELECTROPHILE I HAVE A + CHARGE or ad+ CHARGE. I ATTACK ELECTRON RICH AREAS SUCH AS C=C DOUBLE BONDS.

  7. MEET THE ATTACKERS Press the space bar

  8. MEET 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!

  9. WHO IS ATTACKED? THE BONDING IN A MOLECULE INFLUENCES WHAT WILL ATTACK IT

  10. WHO IS ATTACKED? THE BONDING IN A MOLECULE INFLUENCES WHAT WILL ATTACK IT SINGLE A typical covalent bond with one shared pair – nothing to tempt an attacking species

  11. WHO IS ATTACKED? THE BONDING IN A MOLECULE INFLUENCES 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

  12. WHO IS ATTACKED? THE BONDING IN A MOLECULE INFLUENCES 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

  13. WHO IS ATTACKED? THE BONDING IN A MOLECULE INFLUENCES 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 d+ d- 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

  14. WHO IS ATTACKED? THE BONDING IN A MOLECULE INFLUENCES 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 d+ d- 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

  15. WHAT ATTACKS ALKANES? ALKANES ARE RELATIVELY UNREACTIVE ORGANIC COMPOUNDS ALKANES CONTAIN TWO BOND TYPES C-H and C-C 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 SUBSTITUTION

  16. WHAT ATTACKS ALKENES? ALKENES ARE MUCH MORE REACTIVE THAN ALKANES ALKENES CONTAIN A C=C BOND There will be twice as many electrons between the carbon atoms as there are in a single bond C=C bond is double – an electron rich area Bonds are non-polar - no electron deficient areas ELECTROPHILIC ADDITION

  17. WHAT ATTACKS HALOGENOALKENES? HALOGENOALKANES ARE MUCH MORE REACTIVE THAN ALKANES HALOGENOALKANES CONTAIN A POLAR BOND The halogen is more electronegative than the carbon attracts the shared electron pair. d+ d- 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 SUBSTITUTION

  18. CURLY ARROWS THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS

  19. CURLY ARROWS THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS ELECTRONS MOVE FROM AREAS OF HIGH ELECTRON DENSITY TO ONES WITH A LOWER ELECTRON DENSITY

  20. CURLY ARROWS THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS ELECTRONS MOVE FROM AREAS OF HIGH ELECTRON DENSITY TO ONES WITH A LOWER ELECTRON DENSITY For example… from LONE PAIRS DOUBLE BONDS

  21. CURLY ARROWS THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS ELECTRONS MOVE FROM AREAS OF HIGH ELECTRON DENSITY TO ONES WITH A LOWER ELECTRON DENSITY For example… from LONE PAIRS DOUBLE BONDS to POSITIVE SPECIES THE d+ END OF POLAR BONDS

  22. CURLY ARROWS THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS

  23. CURLY ARROWS THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS ARROWS WITH TWO ‘HEADS’ INDICATE THE MOVEMENT OF TWO (A PAIR OF) ELECTRONS

  24. CURLY ARROWS THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS ARROWS WITH TWO ‘HEADS’ INDICATE THE MOVEMENT OF TWO (A PAIR OF) ELECTRONS A PAIR of electrons moves from here… to here

  25. CURLY ARROWS THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS ARROWS WITH TWO ‘HEADS’ INDICATE THE MOVEMENT OF TWO (A PAIR OF) ELECTRONS A PAIR of electrons moves from here… to here ARROWS WITH ONE ‘HEAD’ INDICATE THE MOVEMENT OF JUST ONE ELECTRON

  26. CURLY ARROWS THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS ARROWS WITH TWO ‘HEADS’ INDICATE THE MOVEMENT OF TWO (A PAIR OF) ELECTRONS 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

  27. CURLY ARROWS THESE ARE USED TO REPRESENT THE MOVEMENT OF ELECTRONS ARROWS WITH TWO ‘HEADS’ INDICATE THE MOVEMENT OF TWO (A PAIR OF) ELECTRONS 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 ALWAYS BE PRECISE WITH THE POSITIONING OF ANY ARROWS

  28. DRAWING CURLY ARROWS NUCLEOPHILES:- possess a lone pair of electrons

  29. lone pair negative charge H O HYDROXIDE ION more lone pairs DRAWING CURLY ARROWS NUCLEOPHILES:- possess a lone pair of electrons

  30. lone pair negative charge H O HYDROXIDE ION more lone pairs H H N lone pair H DRAWING CURLY ARROWS NUCLEOPHILES:- possess a lone pair of electrons AMMONIA MOLECULE Nucleophiles don’t need to have negative charge… BUT they must have a lone pair

  31. lone pair negative charge H O HYDROXIDE ION more lone pairs H H N lone pair H DRAWING CURLY ARROWS NUCLEOPHILES:- possess a lone pair of electrons AMMONIA MOLECULE Nucleophiles don’t need to have negative charge… BUT they must have a lone pair

  32. DRAWING CURLY ARROWS ELECTROPHILES:- attract a lone pair of electrons

  33. DRAWING CURLY ARROWS ELECTROPHILES:- attract a lone pair of electrons There are no electrons in the outer shell of hydrogen so it has space to accept two electrons H HYDROGEN ION

  34. d+ d- H Cl DRAWING CURLY ARROWS ELECTROPHILES:- attract a lone pair of electrons There are no electrons in the outer shell of hydrogen so it has space to accept two electrons H HYDROGEN ION contains a POLAR BOND; the d+ end will attract the electron pair HYDROGEN CHLORIDE

  35. d+ d- H Cl DRAWING CURLY ARROWS ELECTROPHILES:- attract a lone pair of electrons There are no electrons in the outer shell of hydrogen so it has space to accept two electrons H HYDROGEN ION contains a POLAR BOND; the d+ end will attract the electron pair HYDROGEN CHLORIDE

  36. DRAWING CURLY ARROWS ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. H H d+ d- H O H C C Br H C C O H 3 3 H H Br This is the basic mechanism for the nucleophilic substitution of bromoethane.

  37. DRAWING CURLY ARROWS ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. H H d+ d- H O H C C Br H C C O H 3 3 H 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.

  38. Br DRAWING CURLY ARROWS ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. H H H O H C C Br H C C O H 3 3 H H

  39. DRAWING CURLY ARROWS ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. 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

  40. DRAWING CURLY ARROWS ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. H d+ d- H O H C C Br 3 H In bromoethane, C2H5Br, the C-Br bond is polar because the electronegativity of Br is greater than C. It will susceptible to attack by nucleophiles.

  41. DRAWING CURLY ARROWS ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. H d+ d- H O H C C Br 3 H A pair of electrons moves from th hydroxide ion to the slightly positive carbon in bromoethane.

  42. DRAWING CURLY ARROWS ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. H d+ d- H O H C C Br 3 H Carbon has a full outer shell of eight electrons so as two come in, two must leave.

  43. DRAWING CURLY ARROWS ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. H H O H C C Br 3 H The C-Br bond breaks as the shared pair of electrons move onto the bromine.

  44. Br DRAWING CURLY ARROWS ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. H H H O H C C Br H C C O H 3 3 H H

  45. Br DRAWING CURLY ARROWS ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. H H H O H C C Br H C C O H 3 3 H H

  46. Br DRAWING CURLY ARROWS ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. H H H O H C C Br H C C O H 3 3 H H

  47. Br DRAWING CURLY ARROWS more lone pairs ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. d+ d- H H d+ d- H O H C C Br H C C O H 3 3 H H

  48. Br DRAWING CURLY ARROWS more lone pairs ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. H H d+ d- H O H C C Br H C C O H 3 3 H H

  49. Br DRAWING CURLY ARROWS more lone pairs ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. d+ d- H H d+ d- H O H C C Br H C C O H 3 3 H H

  50. DRAWING CURLY ARROWS ‘BALANCING THE BOOKS’ When moving electrons about, it is essential to check that the charges on the reactants and products balance. negative charge lone pair H O more lone pairs NUCLEOPHILIC SUBSTITUTION d+ d-

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