1. Physical Chemistry Chapter VI Interaction between Molecules 2019/5/16
Chemistry Department of Fudan University

2. 1873---van der Waals 1910 Noble Prize in Physics
§6−1 Intermolecular interaction
Weak interactions between molecules
van der Waals
1910 Noble Prize in Physics
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Chemistry Department of Fudan University

3. Chemistry Department of Fudan University
(1) Electrostatic interaction
Keesom
Dipole-dipole interactions between two polar molecules
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Chemistry Department of Fudan University

4. Chemistry Department of Fudan University
(2) Dipole-Induced-dipole interaction
Debye
A molecule with permanent dipole can induce a dipole of a neighboring polarizability molecule (polarizability a). The interaction of the induced dipole with the permanent dipole can be written as:
2019/5/16
Chemistry Department of Fudan University

5. For similar molecules, if 1=2=, 1=2=, then
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6. Transient dipole interactions Chemistry Department of Fudan University
(3) Dispersion interaction
Transient dipole interactions
London
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7. (4) Total Energy of intermolecular interactions
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8. Partition of van der Waals interaction
Dipole moment
Polarizability
molecule
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9. Chemistry Department of Fudan University
The interaction energy of AB can be obtained using Variational Principle (Quantum mechanics)
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10. Chemistry Department of Fudan University
(5) Intermolecular potential energy
(n=8-16)
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11. n=6, m=12 Lennard-Jones potential energy 2019/5/16
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12. Chemistry Department of Fudan University
Lennard-Jones potential energy curve
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13. Chemistry Department of Fudan University
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14. Chemistry Department of Fudan University
Van der Waals radius
Primary alkane
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15. §6−2 Intermolecular interactions of gas
For ideal gas :
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16. (1) Real gas and van der Waals equation
For ideal gas, Z=1
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17. Chemistry Department of Fudan University
Ideal gas
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18. Virial equation of state Chemistry Department of Fudan University
B, C, D: the second, third and fourth Virial coefficient
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19. Chemistry Department of Fudan University
Van der Waals equation:
Vm= V / n
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20. (2) Critical and supercritical
Critical point
Critical pressure
Critical volume
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21. (3) Corresponding state law Chemistry Department of Fudan University
Reduced variables:
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22. Chemistry Department of Fudan University
nitrogen
methane
propane
ethylene
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23. Chemistry Department of Fudan University
At the critical point, pr, Tr and Vr all equal to 1
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Chemistry Department of Fudan University

24. Chemistry Department of Fudan University
2019/5/16
Chemistry Department of Fudan University

25. §6−3 Intermolecular interactions in liquid
1. The structure of liquid and radial distribution function J(R)
The structure of liquid is the spatial distribution and arrangement of liquid molecules
Long range---- disordered
Short range--- ordered but components vary all the time
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Chemistry Department of Fudan University

26. Chemistry Department of Fudan University
The structure of liquid can usually be described by the radial distribution function, J(R) or the pair-correlation function g(R)：
---average particle density of liquid
J(R)dR is the probability of finding another particle within a spherical shell with radius R and thickness dR defined by the center particle.
2019/5/16
Chemistry Department of Fudan University

27. Chemistry Department of Fudan University
Peak is close to the minimum of U2(R)
wide-shell structure
g2(R) ≈ 0 due to molecular repulsion
Typical radial distribution curve of simple liquid
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Chemistry Department of Fudan University

28. Chemistry Department of Fudan University
The structure of liquid mainly depends on the density of liquid and is less perturbed by temperature Ar
The J(R) curves of liquid Ar at different temperatures
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Chemistry Department of Fudan University

29. Chemistry Department of Fudan University
The J(R) curves of liquid Ar at different densities
As the increase of liquid density, the population of short-range ordered structures also increases
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30. Chemistry Department of Fudan University
if define the coordination number of liquid (Z) as the number of particles at the first coordination spherical shell, then Z is
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31. Chemistry Department of Fudan University
2. Measurement and calculation of J(R)
The radial distribution function can be determined experimentally by X-ray or neutron diffraction
Diffraction intensity can be correlated with diffraction angle:
where
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Chemistry Department of Fudan University

32. Chemistry Department of Fudan University
Theoretical calculation of J(R)
VN—potential energy
Molecular dynamics
Monte Carlo simulation
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33. 2. Supermolecule assembly Chemistry Department of Fudan University
§6-4 Supermolecule chemistry and molecular assembly
Supermolecule chemistry is concerned with molecular assemblies with special structure and function, consisting of two or more chemical species glued together through intermolecular interaction.
1. Supermolecule
several components: donor and acceptors
a vast number of components
2. Supermolecule assembly
such as films, colloids
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Chemistry Department of Fudan University

34. Intermolecular interactions in supermolecule
Electrostatic
Hydrogen bonding
Metal-ligand interaction
- stacking
Induced dipole-induced dipole interaction
Hydrophobic effect
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35. Chemistry Department of Fudan University
Molecular recognition
Supermolecular self-assembly
Donor and acceptor selectivity
Ordered structure
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36. Crown ether and cryptand
Molecular recognition between crown ether and NH4+
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Chemistry Department of Fudan University

37. Chemistry Department of Fudan University
Hydrogen bonding recognition and self-assembly
2019/5/16
Chemistry Department of Fudan University