8/7/2019 59-261_Unit+1_W2011_CLEW (3)

1/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

2/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

3/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

4/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

5/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

6/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

7/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

8/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

9/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

10/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

11/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

12/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

13/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

14/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

15/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

16/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

17/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

18/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

19/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

20/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

21/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

22/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

23/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

24/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

25/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

26/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

27/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

28/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

29/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

30/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

31/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

32/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

33/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

34/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

35/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

36/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

37/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

38/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

39/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

40/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

41/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

42/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

43/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

44/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

45/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

46/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

47/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

48/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

49/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

50/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

51/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

52/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

53/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

54/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

55/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

56/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

57/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

58/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

59/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

60/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

61/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

62/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

63/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

64/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

65/88

59-261

T itration cur v es of weak acids and bases (1 )

? A

5

H A c

HA c

1.74 10 M

aK

!

! v

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

66/88

59-261

T itration cur v es of weak acids and bases (2 )

A buffer resists changes in pH

Titration curves showgraphically that a weak acid andits anion can act as a buffer .

The useful buffering region of aweak acid is generally between10% and 90% titration of theweak acid.

Buffering region depends on p K a

Buffering region spansapproximately pK a 1.0

Figure 2-17

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

67/88

59-261

Henderson-Hasselbalch examples1 a) Calculate the pKa of lactic acid at pH 4.8 [lactate]=0.087 M; [lactic acid]= 0.010

M.

b) What will the pH of the above solution be upon addition of 0.007 M HCl?

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

68/88

59-261

Case 1- A dd acid to a buffer:

Where x= [H+

] addedpH= pKa+ log ([A -]- x)/([H A ] + x)

Case 2- add base to a buffer

Where y= [OH -] added

pH= pKa+ log ([A -] + y)/([H A ] - y)

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

69/88

59-261

A nother example:A solution was made by mixing 100 mL of 0.1 M HCl with 400 mL of 0.1 M

sodium acetate, and diluting the mixture to 1 L. What is the pH of thesolution? (The p K a of acetic acid is 4.76)

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

70/88

59-261

Polyprotic acids as buffers

Figure 2-18

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

71/88

59-261

Henderson-Hasselbalch examples2. What is the predominant species of H3PO4, H2PO4 , HPO42 and PO43 at pH = 6.0?

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

72/88

59-261

Henderson-Hasselbalch examples2. What is the predominant species of H3PO4, H2PO4 , HPO42 and PO43 at pH = 6.0?

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

73/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

74/88

59-261

Buffering of blood plasma

24

3

[CO ( g)][H ]

[HCO ]K !

[H+] concentration can be controlled by regulating[CO2(g)] in the lungs and the [HCO3 ] in the blood.

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

75/88

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

76/88

59-261

Learning objecti v es

Understand how water and weak acids ionizeCalculate pH/pOH from [H +] or [OH -]Use Henderson-Hasselbalch equation tocalculate pH s, pKa s, and concentrations of ionic speciesUnderstand titration cur v es and buffers.

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

77/88

59-261

Unit 1 Foundations______________________________

Stereochemistry, configuration andconformation

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

78/88

59-261

Learning Objecti v es

Understand configuration

versus conformationUnderstand Enantiomers v ersus

diastereomersBe able to identify chiral centersUnderstand RS system

Determining absolute configuration Drawing molecules of a particular absolute

configuration

h

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

79/88

59-261

3D structure: StereochemistryStereoisomers : different molecules in which the bond order is the same but thespatial arrangement of the atoms is different .

Structural formula ball and stick space filling

Space filling is the most realistic : radius of each atom is proportional to its van der

Waals radius .

f

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

80/88

59-261

3D structure: ConfigurationConfiguration : the fixed spatial arrangement of atoms.

Is conferred by:(i) double bonds (no freedom of rotation); or

(ii) chiral centres (the specific sequence of arrangement of groups).

Geometric (cis-trans) isomers : arrangement differs with respect to double bond.

Example :These can be separated and havetheir own unique properties.

3D Chi li (1 )

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

81/88

59-261

3D structure: Chirality (1 )Asymmetric carbon :

a C atom with 4 differentsubstituents.

The substituents may be arrangedin 2 different ways in 3-D space .

Gives rise to 2 stereoisomers withsimilar or identical chemicalproperties, but with certaindiffering physical and biologicalproperties.

Asymmetric carbon centres arechiral .

Non-chiral carbons are symmetricor achiral .

3D Chi li (2 )

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

82/88

59-261

3D structure: Chirality (2 )Presence of 2 or more ( n ) chiral centres in a molecule results in 2 n stereoisomers .

Enantiomers : stereoisomers that are mirror images of each other.

Diastereomers : stereoisomers that are not mirror images of each other.

S d f i

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

83/88

59-261

Structure and functionEnantiomers have nearly identical chemical properties, however, they rotate plane-polarized light in opposite directions .

In biochemistry: structure and function are intimately related .

Biological interactions are stereospecific , e.g., enzymes, hormones, immuneresponses.

T h lid id C f hi li

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

84/88

59-261

T halidomide: Consequences of chirality

Has 1 chiral centre: 2 enantiomers.

Late 1957 to the early 60 s:

used for treating morning sickness inpregnant women.

S enantiomer : an effective sedative.

Many babies died, while 10,000 wereborn world-wide with, for example,stunted arms and legs.

R enantiomer :

teratogenic; malformation causing.

Could it have been averted?

M l l f i

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

85/88

59-261

Molecular conformationRefers to the spatial arrangement of substituents that are free to assume different

configurations in space by the free rotation (no breaking) about single bonds.Rotational barriers due to steric hindrance and/or electronic factors.

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

86/88

St ifi it

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

87/88

59-261

StereospecificityIn general, biomolecules in organisms occur in only one of their stereoisomers.

Amino acids in proteins occur as the L-relative isomers.

Glucose, a sugar, occurs in the (R absolute) or D-relative configuration.

Living systems are able to

control the chirality of themolecule synthesized as theenzymes involved are chiral.

Enzymes and proteins arestereospecific : they are able

to distinguish betweenstereoisomers.

L i g Obj ti

8/7/2019 59-261_Unit+1_W2011_CLEW (3)

88/88

Learning Objecti v es

Understand configuration v ersus conformationUnderstand Enantiomers v ersusdiastereomersBe able to identify chiral centersUnderstand RS system

Determining absolute configuration Drawing molecules of a particular absolute

configuration