A free review of chemical reactions in organic chemistry provided by Examville

1. Unit One Part 6:
analysing chemical reactions
at last...chemical
reactions!

2. 6
Unit One
Part reactions (pg69-70)
Balanced
Reaction types (pg71-72)
Reagents (pg72-77)

3. Chemistry...
NUCLEOPHILE ELECTROPHILE
electron rich electron poor
high electron low electron
density density
this slide sums up
the majority of
chemical reactions
(even the funkier ones
follow these
...it’s that simple
principles)

4. Chemistry...
NUCLEOPHILE ELECTROPHILE
electron rich electron poor
high electron low electron
density density
...so that was a
quick lecture...
...it’s that simple

5. lets look at a simple
reaction...
lets just show its
that simple (we do
have 50 minutes to
kill after all)

6. the Lucas test
H3C H3C
ZnCl2 (aq)
H3C OH + HCl H3C Cl + H2O
H3C H3C
the Lucas test is
simple...you’ll do it lab
this week...two water
soluble compounds
react...
water soluble water soluble water insoluble
H-bond ion-dipole two layers

7. the Lucas test
H3C H3C
ZnCl2 (aq)
H3C OH + HCl H3C Cl + H2O
H3C H3C
to give an insoluble
compound. Why
insoluble? (no longer
able to H-bond)
water soluble water soluble water insoluble
H-bond ion-dipole two layers

8. the Lucas test
H3C H3C
ZnCl2 (aq)
H3C OH + HCl H3C Cl + H2O
H3C H3C
}
}
reactants products
stoichiometry
1 : 1 :
simple
definitions
1 : 1

9. the Lucas test
H3C H3C
ZnCl2 (aq)
H3C OH + HCl H3C Cl + H2O
H3C H3C
ratio of
}
}
compounds in
reaction
reactants products
stoichiometry
1 : 1 : 1 : 1

10. ...simply count atoms (or electrons)...
sorting out the
stoichiometry is
easy...just make sure you
have the same number of
atoms on both sides of
the equation and
remember...

11. NO
atoms (or electrons)
we only move
them (or change
the bonds)
created or destroyed

12. unfortunately,
chemists are lazy...
a quick word of
warning...organic chemists
are a little lazy and often
miss side products off their
reaction schemes!

13. depiction of a standard reaction
OMe OMe
H2SO4
HO3S
...so, here is a
standard reaction as
shown in many text
books...

14. depiction of a standard reaction
OMe OMe
H2SO4
HO3S
...problem is, it
doesn’t show
everything...so lets
have a closer look...

15. so what bonds are
broken?

16. depiction of a standard reaction
redraw sulfuric acid
and it becomes
clear that we will
loose an OH...
OMe OMe
HO SO3H
HO3S
obviously lost OH

17. depiction of a standard reaction
OMe OMe
HO SO3H
HO3S
...we can’t just add it to
the aryl ring or one C
would have too many
electrons...
obviously lost OH

18. depiction of a standard reaction
OMe OMe
HO SO3H
H HO3S
remember we don’t always draw H

19. depiction of a standard reaction
OMe OMe
HO SO3H O
H H
H HO3S
...overall we have
lost H from
aromatic and OH
from acid...or water
which means we ‘forgot’ to add HOH

20. depiction of a standard reaction
OMe OMe
HO SO3H O
H H
H HO3S
which means we ‘forgot’ to add HOH

21. depiction of a standard reaction
OH
HO Me Br O
O Me
HO
O OMe
O
O OMe

22. depiction of a standard reaction
H
O
HO Me Br O
O Me
HO
O OMe ...break O–H bonds...
O
O OMe
all the bonds broken & formed

23. depiction of a standard reaction
H
O
HO Me Br O
O Me
HO
O OMe
O
O ...break C–Br bond...
OMe
all the bonds broken & formed

24. depiction of a standard reaction
...form C–O bond
AND H–Br
H
O
HO Me Br O
H Br
O Me
HO
O OMe
O
O OMe
...and the ‘mystery’ product

25. depiction of a standard reaction
H
O
HO Me Br O
H Br
O Me
HO
O OMe
O
O OMe
1 3 1 3
don’t forget the stoichiometry

26. what is happening
in a reaction?

27. it is the movement
of electrons

28. Lewis structures
here is the Lucas
reaction again...
H3C H3C
H3C OH + + H3C Cl + O
Cl H H H
H3C H3C
as each bond is two electrons
we have just moved electrons...

29. Lewis structures
H H
H C H H C H
H H H
Cl
H C C O H H C C Cl O H
HH H HH
C H C H
H H
H3C H3C
H3C OH + + H3C Cl + O
Cl H H H
...and here is the
H3C H3C
Lewis structures
as each bond is two electrons
we have just moved electrons...

30. Lewis structures
...we take O with its
complete octet of
electrons and share
H two of them with H H
to...
H C H H C H
H H H
Cl
H C C O H H C C Cl O H
HH H HH
C H C H
H H
H3C H3C
H3C OH + + H3C Cl + O
Cl H H H
H3C H3C
as each bond is two electrons
we have just moved electrons...

31. Lewis structures
H H
...form water...
H C H H C H
H H H
Cl
H C C O H H C C Cl O H
HH H HH
C H C H
H H
H3C H3C
H3C OH + + H3C Cl + O
Cl H H H
H3C H3C
as each bond is two electrons
we have just moved electrons...

32. Lewis structures
...then we share the
electrons of the chloride
octet to make sure the
original C is still an a
happy octet...
H H
H C H H C H
H H H
Cl
H C C O H H C C Cl O H
HH H HH
C H C H
H H
H3C H3C
H3C OH + + H3C Cl + O
Cl H H H
H3C H3C
as each bond is two electrons
we have just moved electrons...

33. Lewis structures
H H
H C H H C H
H H H
Cl
H C C O H H C C Cl O H
HH H HH
C H C H
H H
H3C H3C
H3C OH + + H3C Cl + O
Cl H H H
so just swapped
H3C H3C
electrons around...
as each bond is two electrons
we have just moved electrons...

34. what types of
reaction are there?

35. 3
basic
reactions

36. substitution
reactions
A B + C A C + B
does what it says...the
reagent swaps with a
functional group in our
molecule...

37. substitution
reactions
OH OH
Br CH3NH2 NHCH3 H Br
here’s an example from the
synthesis of prozac® where an
amine substitutes / displaces /
exchanges with a bromide...

38. substitution
reactions
Na O
Cl O
NHCH3 NaCl
NHCH3 F3C
F3C
fluoxetine
here is another example finishing the
Prozac®
synthesis of prozac®; an alkoxide
(alcohol derivative) substitutes a
chloride...

39. A + Y A Y
two molecules add
together or combine...all
atoms in both starting
addition
materials are found in the
product
reactions

40. CH3
CH3
H Br Br
H
here hydrogen
bromide adds across
an alkene to give us a
addition
new bromide
reactions

41. at some point you’ll have to
learn why it adds the bromide
to the more hindered end of the CH3
CH3alkene...but that’s someone
else’s job! Br
H Br
H
addition
reactions

42. O H3C O MgBr
H3C MgBr CH3
CH3
Ph Ph
here a Grignard reagent
is adding to a ketone to
give (eventually) an
addition
alcohol
reactions

43. elimination
reactions
A X A + X
elimination is the opposite
of addition...we rip a bit of
the molecule off.

44. elimination
reactions
OH
CH3 CH3
O
H H
H
this example shows
the elimination of
water (dehydration) to
form an alkene

45. elimination
reactions
CH3 Br
H3C CH3
H3C
H3C H Br
H3C
H
or the elimination of
hydrogen bromide
(hydrobromic acid) to
form an alkene

46. what reagents are
involved in these
reactions?
now we know what reactions
we can perform...what
reagents can we use?

47. nucleophiles
2
electron rich molecules
nucleophiles are electron
rich compounds that
donate two electrons to
form a new bond...
examples include...
donateelectrons

48. anions
H O ≡ H O Br ≡ Br
3 lone pairs 4 lone pairs
H
H3C
≡ Pr C
H
1 lone pair

49. anions
H O ≡ H O Br ≡ Br
negatively charged
compounds that possess a
3 lone pairs
lone pair of electrons that 4 lone pairs
can form a new bond
H
H3C
≡ Pr C
H
1 lone pair

50. anions
nucleophilic reaction
O H O
H H H

51. anions
nucleophilic reaction
hydroxide donates a
pair of electrons to
form a new bond to
proton
O H O
H H H

52. anions
nucleophilic reaction
O H O
H H H
note: both sides of
equation have same
charge (both are
neutral overall)

53. anions
nucleophilic reaction
O H O
H H H
note: both sides of
equation have same
charge (both are this is a good sign that you’ve
neutral overall) got the reaction right!

54. lone pairs
lone pairs as
nucleophile
O N S
H H H H H3C CH3
H
water ammonia dimethyl sulfide
(DMS)
lone pairs on neutral
molecules are also good
nucleophiles...

55. lone pairs
nucleophilic reaction
H
N H Cl N Cl
H H H H
H H

56. lone pairs
nucleophilic reaction
ammonia donates a
pair of electrons to
form a new bond to
hydrogen chloride
H
N H Cl N Cl
H H H H
H H

57. lone pairs
nucleophilic reaction
can’t have two bonds to H
(4 electrons) so break H–
Cl bond with electrons
flowing towards most
electronegative element
H
N H Cl N Cl
H H H H
H H

58. lone pairs
nucleophilic reaction
H
overall its been a
N H Cl
substitution N Cl
H H H H
H H

59. lone pairs
nucleophilic reaction
H
N H Cl N Cl
H H H H
H H
note: overall both sides
are neutral (have same
charge)

60. bonds bonds can also be a
source of electrons...and
these cause confussion!
δ– δ+ H
C Y
Y=Li, Mg B
H H
nucleophilic H
site
reactive
σ bond
H H
C C
H H R
high electron density R = electron
nucleophile donating group

61. electrophiles
2
electron poor molecules
the other kind of reagents
are...electrophiles are electron
poor compounds that accept two
electrons to form a new bond...
examples include...
acceptelectrons

62. proton
H ≡ H
empty 1s orbital
no electrons!
simplest electrophile...it
has no electrons and
desperately wants some!

63. proton
electrophilic reagent
H H
H
O H O
H H

64. proton
electrophilic reagent
H H
H
O H O
H H
nucleophilic water
donates two electrons to
proton, which accepts
them to form new bond

65. Group 13
F
F Cl
F B Cl Al F B
F Cl F
empty 2p empty 3p
orbital orbital have 6 valence
only
electrons...need 8 to obey
octet rule so happily accept a
pair of electrons

66. bonds
δ+ δ– Y = Cl, δ+ δ–
C Y Y = O,
Br, N, O C Y NR
electrophilic electrophilic
site site
bonds can be
electrophiles if they are
polarised and have a δ+
centre

67. bonds
electrophilic reagent
H H
O
O H O O
H H3C CH3
H3C CH3

68. is it that easy?

69. nucleophile + electrophile product
yup, this equation sums up
the majority of reactions...

70. yes!

71. ...and no...

72. H3C δ+ δ– H3C δ+ δ–
H3C O H3C Cl
H3C H H3C
polarity in these two
compounds looks the
same...so do they behave in
the same way??

73. H3C δ+ δ– H3C δ+ δ–
H3C O H3C Cl
H3C H H3C
of course not!
this is chemistry after all...

74. H3C δ+ δ– H3C δ+ δ–
H3C O H3C C Cl
alcohol uses lone
H3C H H3C pair to act as a
nucleophile
nucleophile electrophile

75. H3C δ+ δ– H3C δ+ δ–
H3C O H3C C Cl
chloride isC
H3 an H H3C
electrophile
nucleophile electrophile

76. ...you will learn to to
identify which is which...

77. so what actually
happens in a reaction?

78. H3C O H3C Cl H
H + H Cl + O
H3C H3C
CH3 CH3 H
so here’s the Lucas
test again...overall
it’s a substitution of
hydroxyl for chlorine
what order are the
bonds made and broken?

79. H3C O H3C Cl H
H + H Cl + O
H3C H3C
CH3 CH3 H
what order are the
bonds made and broken?

80. H
H3C O H3C O
H H H
H3C H3C
CH3 CH3
CH3 CH3 H
H3C C O H H H3C C O H
CH3 CH3
addition
step
step
one

81. H
H3C O H3C O
H H H
H3C H3C
CH3 CH3
nucleophilic alcohol
CH3 donates 2 electrons to
CH3 H
a proton from H–Cl in
H3C C O H H anH3C Creaction
addition O H
CH3 CH3
addition
step
step
one

82. H
H3C O H3C O
H H H
H3C H3C
CH3 CH3
note: octet rule is
obeyed and the
charge is the same
CH3 on both sides CH3 H
(positive)
H3C C O H H H3C C O H
CH3 CH3
addition
step
step
one

83. H CH3 H
H3C O
H O
H3C H3C CH3
CH3 H
H H
H C H H C H
H H H H
H C C O H H C C O H
HH HH
C H C H
H H
step
two elimination

84. H CH3 H
H3C O
H O
H3C H3C CH3
CH3 H
H H
elimination of
H C H H water...molecule splits in
C H
H H H two...electrons go with
H
most electronegative
H C C O H H C C atom O H
HH HH
C H C H
H H
step
two elimination

85. H CH3 H
H3C O
H O
H3C H3C CH3
CH3 H
charge is the same
H on both sides (positive)... H
we now have a reactive
H C H intermediate H C H
H H H H
(charged species with 6
H C C O H electrons) H C C O H
HH HH
C H C H
H H
step
two elimination

86. CH3 H3C Cl
Cl H3C
H3C CH3 CH3
H H
H C H H C H
H H
H C C Cl H C C Cl
HH HH
C H C H
H H
addition
step
step
three

87. CH3 H3C Cl
Cl H3C
H3C CH3 CH3
H H
H C H H C
finally, second H
H H
addition step to
H C C Cl H C
complete octet C Cl
HH HH
C H C H
H H
addition
step
step
three

88. CH3 H3C Cl
Cl H3C
H3C CH3 CH3
H H
H C H H C H
H H
H C C Cl H C C Cl
HH HH
C H C H
H H
nucleophile donates two
electrons to electrophile
addition
step
that accepts them to
step form new bond
three

89. CH3 H3C Cl
Cl H3C
H3C CH3 CH3
H H
H C H H C H
H H
H C C Cl H C C Cl
HH note: the charge is HH
C H the same on both C H
sides (neutral)
H H
addition
step
step
three

90. 3
steps
1
substitution
reaction

91. another
representation...
we can follow the change of
energy during a reaction...in a
reaction profile

92. reaction profile
energy
Cl
+
H2O
H
O + Cl
H
OH + HCl
reaction
progress Cl + H2O

93. reaction profile
each hill represents
one step in our
reaction
energy
Cl
+
H2O
H
O + Cl
H
OH + HCl
reaction
progress Cl + H2O

94. reaction profile
each dip
represents an
intermediate we
can see
energy
Cl
+
H2O
H
O + Cl
H
OH + HCl
reaction
progress Cl + H2O

95. reaction profile
higher the hill, the
harder the step
energy
Cl
+
H2O
H
O + Cl
H
OH + HCl
reaction
progress Cl + H2O

96. reaction profile
the lower in energy
any stage the more
stable it is
energy
Cl
+
H2O
H
O + Cl
H
OH + HCl
reaction
progress Cl + H2O

97. just one hill, so
just one step
energy
HO
CH3Br
Br
reaction CH3OH
progress

98. no dip so no
intermediates
energy
HO
CH3Br
Br
reaction CH3OH
progress

99. direct
energy
substitution
would look like
this HO
CH3Br
Br
reaction CH3OH
progress
HO + CH3Br CH3OH + Br

100. once again, you will learn
energy
more about this but not
from me! Why don’t I get
HO
to teach the cool stuff? CH3Br
Br
reaction CH3OH
progress
H 1 H 1 H
SLOW 2 δ– 2 δ–
HO + Br HO Br Nu + Br
H RDS H
H H H H
transition state

101. what have
....we learnt?
• analyse reactions
• classify reagents
•r e a c t i o n t y p e s
Picture: © Pittsburgh Supercomputing Center