Could London Dispersion Force Control Regioselective (2 + 2) Cyclodimerizations of Benzynes? YES: Application to the Synthesis of Helical Biphenylenes

2017 ◽

Vol 376 (2112) ◽

pp. 20170047 ◽

Cited By ~ 12

Author(s):

Yoshiharu Nishiyama

Keyword(s):

Hydrogen Bond ◽

Hydrogen Bonds ◽

Molecular Modelling ◽

Hydroxyl Group ◽

Enthalpy Of Sublimation ◽

Dispersion Force ◽

Hydroxyl Groups ◽

Range Interaction ◽

Simple Arithmetic ◽

London Dispersion

The contribution of hydrogen bonds and the London dispersion force in the cohesion of cellulose is discussed in the light of the structure, spectroscopic data, empirical molecular-modelling parameters and thermodynamics data of analogue molecules. The hydrogen bond of cellulose is mainly electrostatic, and the stabilization energy in cellulose for each hydrogen bond is estimated to be between 17 and 30 kJ mol −1 . On average, hydroxyl groups of cellulose form hydrogen bonds comparable to those of other simple alcohols. The London dispersion interaction may be estimated from empirical attraction terms in molecular modelling by simple integration over all components. Although this interaction extends to relatively large distances in colloidal systems, the short-range interaction is dominant for the cohesion of cellulose and is equivalent to a compression of 3 GPa. Trends of heat of vaporization of alkyl alcohols and alkanes suggests a stabilization by such hydroxyl group hydrogen bonding to be of the order of 24 kJ mol −1 , whereas the London dispersion force contributes about 0.41 kJ mol −1 Da −1 . The simple arithmetic sum of the energy is consistent with the experimental enthalpy of sublimation of small sugars, where the main part of the cohesive energy comes from hydrogen bonds. For cellulose, because of the reduced number of hydroxyl groups, the London dispersion force provides the main contribution to intermolecular cohesion. This article is part of a discussion meeting issue ‘New horizons for cellulose nanotechnology’.

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A Generalization of Electromagnetic Fluctuation-Induced Casimir Energy

Advances in Condensed Matter Physics ◽

10.1155/2015/198657 ◽

2015 ◽

Vol 2015 ◽

pp. 1-10 ◽

Cited By ~ 1

Author(s):

Yi Zheng

Keyword(s):

Thermal Fluctuations ◽

Intermolecular Forces ◽

Casimir Energy ◽

Dispersion Force ◽

Induced Dipole ◽

Macroscopic Objects ◽

Dissipative Media ◽

London Dispersion ◽

Quantum Mechanical Effects ◽

London Dispersion Forces

Intermolecular forces responsible for adhesion and cohesion can be classified according to their origins; interactions between charges, ions, random dipole—random dipole (Keesom), random dipole—induced dipole (Debye) are due to electrostatic effects; covalent bonding, London dispersion forces between fluctuating dipoles, and Lewis acid-base interactions are due to quantum mechanical effects; pressure and osmotic forces are of entropic origin. Of all these interactions, the London dispersion interaction is universal and exists between all types of atoms as well as macroscopic objects. The dispersion force between macroscopic objects is called Casimir/van der Waals force. It results from alteration of the quantum and thermal fluctuations of the electrodynamic field due to the presence of interfaces and plays a significant role in the interaction between macroscopic objects at micrometer and nanometer length scales. This paper discusses how fluctuational electrodynamics can be used to determine the Casimir energy/pressure between planar multilayer objects. Though it is confirmation of the famous work of Dzyaloshinskii, Lifshitz, and Pitaevskii (DLP), we have solved the problem without having to use methods from quantum field theory that DLP resorted to. Because of this new approach, we have been able to clarify the contributions of propagating and evanescent waves to Casimir energy/pressure in dissipative media.

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