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

1873---van der Waals 1910 Noble Prize in Physics §6−1 Intermolecular interaction Weak interactions between molecules 1873---van der Waals 1910 Noble Prize in Physics 2019/5/16 Chemistry Department of Fudan University

Chemistry Department of Fudan University (1) Electrostatic interaction Keesom 1912 Dipole-dipole interactions between two polar molecules 2019/5/16 Chemistry Department of Fudan University

Chemistry Department of Fudan University (2) Dipole-Induced-dipole interaction Debye 1920-1921 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

For similar molecules, if 1=2=, 1=2=, then 2019/5/16 Chemistry Department of Fudan University

Transient dipole interactions Chemistry Department of Fudan University (3) Dispersion interaction Transient dipole interactions 1930----London 2019/5/16 Chemistry Department of Fudan University

(4) Total Energy of intermolecular interactions 2019/5/16 Chemistry Department of Fudan University

Partition of van der Waals interaction Dipole moment Polarizability molecule 2019/5/16 Chemistry Department of Fudan University

Chemistry Department of Fudan University The interaction energy of AB can be obtained using Variational Principle (Quantum mechanics) 2019/5/16 Chemistry Department of Fudan University

Chemistry Department of Fudan University (5) Intermolecular potential energy (n=8-16) 2019/5/16 Chemistry Department of Fudan University

n=6, m=12 Lennard-Jones potential energy 2019/5/16 Chemistry Department of Fudan University

Chemistry Department of Fudan University Lennard-Jones potential energy curve 2019/5/16 Chemistry Department of Fudan University

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

Chemistry Department of Fudan University Van der Waals radius Primary alkane 2019/5/16 Chemistry Department of Fudan University

§6−2 Intermolecular interactions of gas For ideal gas : 2019/5/16 Chemistry Department of Fudan University

(1) Real gas and van der Waals equation For ideal gas, Z=1 2019/5/16 Chemistry Department of Fudan University

Chemistry Department of Fudan University Ideal gas 2019/5/16 Chemistry Department of Fudan University

Virial equation of state Chemistry Department of Fudan University B, C, D: the second, third and fourth Virial coefficient 2019/5/16 Chemistry Department of Fudan University

Chemistry Department of Fudan University Van der Waals equation: Vm= V / n 2019/5/16 Chemistry Department of Fudan University

(2) Critical and supercritical Critical point Critical pressure Critical volume 2019/5/16 Chemistry Department of Fudan University

(3) Corresponding state law Chemistry Department of Fudan University Reduced variables: 2019/5/16 Chemistry Department of Fudan University

Chemistry Department of Fudan University nitrogen methane propane ethylene 2019/5/16 Chemistry Department of Fudan University

Chemistry Department of Fudan University At the critical point, pr, Tr and Vr all equal to 1 2019/5/16 Chemistry Department of Fudan University

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

§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 2019/5/16 Chemistry Department of Fudan University

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

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 2019/5/16 Chemistry Department of Fudan University

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 2019/5/16 Chemistry Department of Fudan University

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 2019/5/16 Chemistry Department of Fudan University

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 2019/5/16 Chemistry Department of Fudan University

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 2019/5/16 Chemistry Department of Fudan University

Chemistry Department of Fudan University Theoretical calculation of J(R) VN—potential energy Molecular dynamics Monte Carlo simulation 2019/5/16 Chemistry Department of Fudan University

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 2019/5/16 Chemistry Department of Fudan University

Intermolecular interactions in supermolecule Electrostatic Hydrogen bonding Metal-ligand interaction - stacking Induced dipole-induced dipole interaction Hydrophobic effect 2019/5/16 Chemistry Department of Fudan University

Chemistry Department of Fudan University Molecular recognition Supermolecular self-assembly Donor and acceptor selectivity Ordered structure 2019/5/16 Chemistry Department of Fudan University

Crown ether and cryptand Molecular recognition between crown ether and NH4+ 2019/5/16 Chemistry Department of Fudan University

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