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

2. 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 orusing the left and right arrow keys on the keyboard KNOCKHARDY PUBLISHING MUDDLE YOUR WAY THROUGH MECHANISMS

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 + or  )

5. MEET THE ATTACKERS Press the space bar

6. MEET THE ATTACKERS I AM AN ELECTROPHILE I HAVE A + CHARGE or a  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. THE BONDING IN A MOLECULE INFLUENCES WHAT WILL ATTACK IT WHO IS ATTACKED?

10. 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 WHO IS ATTACKED?

11. 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 WHO IS ATTACKED?

12. 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 WHO IS ATTACKED?

13. 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 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? 

14. 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 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? 

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

16. 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 WHAT ATTACKS ALKENES? C=C bond is double – an electron rich area Bonds are non-polar - no electron deficient areas ELECTROPHILIC ADDITION

17. 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. 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 SUBSTITUTION

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

34. ELECTROPHILES:- attract a lone pair of electrons DRAWING CURLY ARROWS HYDROGEN ION H There 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 C l 

35. ELECTROPHILES:- attract a lone pair of electrons DRAWING CURLY ARROWS HYDROGEN ION H There 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 C l 

36. DRAWING 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.

37. DRAWING 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.

38. DRAWING 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

39. DRAWING 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

40. DRAWING 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 In bromoethane, C 2 H 5 Br, 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 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 A pair of electrons moves from th hydroxide ion to the slightly positive carbon in bromoethane. 

42. DRAWING 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 Carbon has a full outer shell of eight electrons so as two come in, two must leave. 

43. DRAWING 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 The C-Br bond breaks as the shared pair of electrons move onto the bromine.

44. DRAWING 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

45. DRAWING 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

46. DRAWING 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

47. DRAWING 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 

48. DRAWING 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 

49. DRAWING 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 

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

51. DRAWING 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

52. DRAWING CURLY ARROWS When moving electrons about, it is essential to check that the charges on the reactants and products balance.  negative charge lone pair more lone pairs ‘BALANCING THE BOOKS’ H O H C C Br H 3 H  H C C O H H 3 H Br

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

54. © 2008 JONATHAN HOPTON & KNOCKHARDY PUBLISHING THE END MUDDLE YOUR WAY THROUGH ORGANIC MECHANISMS NOW INVESTIGATE THE MECHANISMS IN DETAIL