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Molecular Interactions

Molecular simulation slide https://docs.google.com/presentation/d/1zPAfSIfWQBJjepRhxKXxmBdB8NUDe6w6/edit?usp=sharing&ouid=114537264942814056043&rtpof=true&sd=true

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Few key types of Intermolecular forces

Electrostatic forces between charged particles

Induction forces between a permanent dipole (or quadrupole) and an induced dipole, a dipole induced in a molecule with polarizable electrons.

Forces of attraction (dispersion forces) and repulsion between nonpolar molecules.

Specific (chemical) forces leading to association and solvation, i.e., to the formation of loose chemical bonds; hydrogen bonds and charge-transfer complexes

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Potential energy Function

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Potential energy Function …

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Electrostatic Forces

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Electrostatic Forces…

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Electrostatic Forces…

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Electrostatic Forces…

Silent feature

Dominant contribution among all intermolecular forces, having inverse of r², While other force having higher power of inverse of rⁿ
Hence it is also having longer range

for example,

ORS having great importance as lifesaving solution during dehydration, to control body ionic and fluid balance.
Conductive of water by small amount of dissolved ions
Higher melting point of salt crystals due higher configurational energy comes from electrostatic force

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Electrostatic Forces and dipole

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Electrostatic Forces for a dipole

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Electrostatic Forces for two dipoles

Suppose two dipoles at r distance, mean 4 charges

The force determine by distance and orientation of dipole axes

-e

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Dipoles effect with Temperature

Thermal (Kinetic) energy result in randomness
Set electric field align the dipoles

Further average potential energy when two dipole interact

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Boltzmann average

For simple diploes it can be written as

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Multipoles

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Quadrupoles

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Polarizability and Induced dipoles

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Polarizability and Induced dipoles

Unit C²J^-1 m^-2

Dimension of volume

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Polarizability and Induced dipoles

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Intermolecular Forces between Nonpolar Molecules

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Ionization in nonpolar molecules

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Ionization in nonpolar molecules…

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Ionization in nonpolar molecules…

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Consideration of attraction and repulsion forces

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Consideration of attraction and repulsion forces

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Consideration of attraction and repulsion forces

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Mie’s potential energy for nonpolar molecules

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Mie’s and Lennard-Jones potential energy for nonpolar molecules

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Mie’s and Lennard-Jones potential energy for nonpolar molecules

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Mie’s and Lennard-Jones potential energy for nonpolar molecules

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Mie’s and Lennard-Jones potential energy for nonpolar molecules

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Potential for Lattice

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Potential for Lattice

Via assuming, m=6 and n=8 to 16The average potential energy of the pair of adjacent molecules 50 % less than corresponding equilibrium separations b/w pair of isolated molecules

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Potential for Lattice

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Statistical Thermodynamics

Relation of Macroscopic System behaviour with Microscopic Properties.

How those particles like atoms, molecules, ions decide bulk properties

Statistical thermodynamics: Statistical mechanics dealing with equilibrium states

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Thermodynamics and quantum state of system

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Ensembles

Ensemble: Large number of imagined systems
Each system having same macroscopic properties (may be different quantum states)

Let suppose,

total energy of real system is “E”

Volume “V”

Number of molecules “N”

Then in case of ensemble every system having same E, V, N

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Ensembles and time average

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Time average …

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Canonical ensemble

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Canonical ensemble …

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Canonical ensemble …

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Canonical ensemble …

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Canonical ensemble …

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Canonical ensemble …

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Canonical ensemble …

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Statistical analogy of thermodynamic properties for NVT

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Statistical analogy of thermodynamic properties for NVT …

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Statistical analogy of thermodynamic properties for NVT … continue

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Other ensembles

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Structural effect

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Hydrogen bond and other specific forces

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Hydrogen bonding …

Hydrogen bonding in solution. Enthalpic effects for two chemically different solutes in cyclohexane at 20°C �

Hydrogen bonding in solution. Volumetric effects for two chemically different solutes in n-hexane at 6°C.

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Hydrogen bonding …

Evidence for hydrogen bonds: Freezing-point data �

Evidence for hydrogen bonds: Enthalpy-of-mixing data

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Osmotic Pressures…

Membrane

P+π

Solvent

Solⁿ

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Osmotic Pressures ..

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Osmometry

Osmotic-pressure data for a-chymotrypsin (circle )(Haynes etal., 1992) in�0.1 M potassium suifate buffer, at pH 5 and 25°C, and for lysozyme (triangle ) and ovalbumin (dimond) (McCarty and Adams, 1987) in 0.06 M cacodylate buffer, at pH 5.8 and 37°C �

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Molecular Theory of Corresponding States

https://pubs.acs.org/doi/10.1021/acs.jpca.7b02135

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