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1. Instrumental techniques
Phar 6521
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3.  Chromatography is a physical method of
separation in which the components to be
separated are distributed between two
phases (KD/P = Distribution/partition constant)
 one of which is stationary (stationary phase)
while the other (the mobile phase) moves
through it in a definite direction.
 The chromatographic process occurs due to
differences in the distribution constant of the
individual sample components.
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Chromatography

4. KD of Cpd A = [A]S / [A]M
KD = Distribution constant of compound A
[A]S = concentration of compound A in stationary phase
[A]M = concentration of compound A in mobile phase
For eg. TLC Chromatography
 compounds distributes itself b/n a liquid mobile phase and a solid
stationary phase
 The rate of migration for a chemical compound is determined by
how much of it distributes into the mobile and stationary phases
Case 1. A compound that distributes itself 100% into the mobile
phase
 will migrate at the same rate of the mobile phase
Case 2: On the other hand, a compound that distributes itself 100%
in the stationary phase
 will not migrate at all 4

5. In most molecular substances, there are
two types of attractive forces:
1. Intramolecular and
2. Intermolecular forces
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 Chromatographic separation is achieved due to
 Different compounds have different KD values
 Distribution constant (KD) is affected by
 the type of intermolecular forces that present in
molecules

6.  force that hold atoms in a single molecule or
a force of attraction within a molecule
e.g. covalent bond, ionic bond
H-Cl, Na
+
Cl
-
Intramolecular forces
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7.  an attraction between two or more separate
molecules.
 are the result of attractions between positively and
negatively charged regions of separate molecules.
 They are not as strong as intramolecular force
(chemical bonds).
Intermolecular forces
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8.  These intermolecular forces as a group
are referred to as van der Waals forces.
There are three types of intermolecular forces,
1. Dipole-dipole interactions
2. Hydrogen bond
3. London force/Dispersion force
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9. A very approximate strength order would be:
Bond type Relative strength
Ionic bonds 1000
Hydrogen bonds 100
Dipole-dipole 10
London forces 1
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10. Intermolecular Forces
 They are, however, strong enough to control
physical properties such as, solubility, boiling
and melting points, vapor pressures, and
viscosities.
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11. Dipole-Dipole Interactions
• Molecules that have
permanent dipoles are
attracted to each other.
√ The positive end of one is
attracted to the negative end of
the other and vice-versa.
√ These forces are only important
when the molecules are close to
each other.
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12.  It occurs in polar compounds
 These work in a similar manner to ionic
interactions, but are weaker because only
partial charges are involved.
 An example of this can be seen in Acetone
Dipole-Dipole Interactions
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13. Dipole-Dipole Interactions
The more polar the molecule, the
higher is its boiling point.
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14. Hydrogen Bonding
Hydrogen bonding occurs when
Hydrogen is bonded to N, O, or F are
unusually strong.
Hydrogen atom has a partial positive
charge and can interact with
another highly electronegative atom
in an adjacent molecule (N, O, or F).
 it is a special type of dipole-dipole
force
The result is a dipolar molecule
 e.g H2O, NH3, HF 14

15. London/Dispersion Forces
 While the electrons in the 1s orbital of helium
would repel each other (and, therefore, tend to
stay far away from each other), it does happen
that they occasionally wind up on the same
side of the atom.
 It involve the attraction between temporarily
induced dipoles 15

16. London/Dispersion Forces
 At that instant, then, the helium atom is
polar, with an excess of electrons on the
left side and a shortage on the right side.
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17. London/Dispersion Forces
 Another helium nearby, then, would have a
dipole induced in it, as the electrons on the
left side of helium atom 2 repel the
electrons in the cloud on helium atom 1.
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18. London/Dispersion Forces
 London dispersion forces, or dispersion
forces, are attractions between an
instantaneous /temporary dipole and an
induced dipole.
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19. London/Dispersion Forces
These forces are present in all molecules,
whether they are polar or non-polar.
The tendency of an electron cloud to distort
in this way is called polarizability.
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20.  This polarization can be induced either by
 A polar molecule or
 A non-polar molecule (the repulsion
of negatively charged electron clouds in
non-polar molecules)
London/Dispersion Forces
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21. 21

22. Factors Affecting London Forces
The strength of dispersion forces tends to
increase with increased molecular weight.
Larger atoms have larger electron clouds, which
are easier to polarize.
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23. Factors Affecting London Forces
The shape of the molecule
affects the strength of
dispersion forces: long, skinny
molecules (like n-pentane tend
to have stronger dispersion
forces than short, fat ones (like
neopentane).
This is due to the increased
surface area in n-pentane.
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24. Which Have a Greater Effect:
Dipole-Dipole Interactions or Dispersion Forces?
• If two molecules are of comparable size
and shape, dipole-dipole interactions will
likely be the dominating force.
• If one molecule is much larger than
another, dispersion forces will likely
determine its physical properties.
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25. Ion-Dipole Interactions
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• A fourth type of force, ion-dipole
interactions are an important force in
solutions of ions.
• The strength of these forces are what make
it possible for ionic substances to dissolve
in polar solvents.

26. Anthocyanins (also anthocyans) are
 belong to a parent class of molecules called flavonoids
 cationic organic compound
 well water-soluble pigments due to ion-dipole interaction

27. Quaternary ammonium cation
are salts of quaternary ammonium cations.
Soluble in water

28.  Polar Molecule
A Molecule with a Positive and Negative Side
Dipole Moment
• A Measure of Molecular Polarity
• A Non-polar Molecule will have a Zero Dipole
Moment
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Molecular Polarity

29. Why is Polarity Important?
 Many Properties Depend on Polarity
Melting and Boiling Point
Surface Tension, Viscosity
Reactivity
Solubility (e.g., will it dissolve in water)
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30. Requirements
 A Polar Molecule Requires
Polar Bonds
A Molecular Shape that Separates the by
the partial Positive from the Negative Side
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31.  Unequal sharing of e- in a bond called Polar
Covalent Bond or Polar Bond
 Partial Charge indicated by delta +/-
Polar Covalent Bonds
-+
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32. Polar Covalent Bonds
 NON-polar covalent bonds
 Bonds between identical atoms such as H-
H, F-F involve equal sharing of e-
 Polar covalent bonds
 Bonds between different atoms involve
unequal sharing of e-
 Polar Covalent Bonds have a Partial
Charge Separation
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33. Electronegativity
 Electronegativity is the ability of an
atom to attract electrons in a bond.
 Nonmetals bonded to N, O, F usually
have polar bonds
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34. Electronegativity Index of Some Elements
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35. Electronegativity
 Used to Determine Bond Polarity
  EN < 0.45 Non-polar Bond
 1.75 >  EN > 0.45 Polar Bond
  EN > 1.75 Ionic Bond Atoms
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Polar or Non-polar Bond?
O-H  EN = 1.4 Polar Bond
C-H  EN = 0.4 Non-polar Bond
C-O  EN = 1.0 Polar Bond
H-Cl  EN = 0.8 Polar Bond

36. Polar Molecules
 The molecule is usually polar
 If all atoms attached to central atom
are not the same
 Or if central atom has 1 or more lone
pairs of electrons
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37. Examples
 Polar compounds
 HCN, H2O, CHCl3, CH2Cl2
 Non-polar
 CO2, CCl4
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38. In Conclusion
 Polarity Determined from
Polar Bonds ( EN > 0.45)
Molecular Shape with + & - sides
N and O in Molecules often lead to
Polar Molecules or Regions
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39. In Conclusion
 Polarity will be important
 In Determining Intermolecular Forces
Vapor Pressure, Boiling and Melting
Points
Surface Tension, Viscosity
 Solubility
 Reactivity (Organic Chemistry)
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40. Intermolecular Forces Affect
Many Physical Properties
The strength of the
attractions between
particles can greatly
affect the properties of a
substance or solution.

41. Solubility
 Defines as the amount of a solute that will dissolve in
a specific solvent at given condition
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Degree of solubility (types of saturation)
Saturated solution: A solution with solute that dissolves
until it is unable to dissolve anymore, leaving the
undissolved substances at the bottom.
Unsaturated solution: A solution (with less solute than the
saturated solution) that completely dissolves, leaving no
remaining substances.
Supersaturated solution: solution (with more solute than
the saturated solution) that contains more undissolved
solute than the saturated solution because of its tendency
to crystallize and precipitate

42. Factors that affects solubility
 The nature of solute and solvent
 Temperature
 Pressure (only applicable to gases)
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43. The nature of solute and solvent
 When two substances are similar they can dissolve in
each other
Polar solutes dissolve in polar solvent
Non-polar solutes tend to dissolve in non-polar solvent
 “Like dissolve like”
 two liquids dissolve in each other b/c the molecules
are alike in polarity
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Note: solvents are grouped either polar or non-polar
solvent
Polar Solvent: a liquid made up of polar molecules
Non-polar Solvent: a liquid made up of non-polar molecules

44. The nature of solute and solvent
 Ionic compounds are made up of charged ions
similar to polar compounds e.g. NaCl
 Ionic compounds are more soluble in polar
solvent than in a non-polar solvent
 ion-dipole interaction
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45. The nature of solute and solvent
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46. Temperature
 Solubility of solids in liquids
 The solubility of a solid increases as temp increases
Solubility of gases in liquid are affected by temperature
 Opposite to the solubility of solids in liquids
As the temperature increases, the solubility of a GAS
in a liquid decreases
WHY ?
 As the temperature increases, the kinetic energy of
the solute gas increases and the gas can escape
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47. Pressure
 when the pressure is increased over the
solvent, the solubility of gas is increased
 WHY ?
 Pressure increases as gas molecules strike the
surface to enter the solution increased
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48. Factors of Dissolving
 Rate of which a solid solute dissolves in a solution
depends on three factors
 Surface area: speed up the solubility by
increasing surface area
 Stirring: increases contact b/n solvent and
solute
 Temperature: kinetic energy increase
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