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Theoretical Consideration Of Solubility
Published in A. L. Horvath, Halogenated Hydrocarbons, 2020
The general tendency of melting and boiling points in a homologous series is to increase with rising molecular weight. The hydrogen-bonding effect is clearly indicated by the difference between the melting and boiling points of non-hydrogen-bonded substances compared with hydrogen-bonded compounds of equal molecular weight. Table 2.29 compares the melting and boiling points of some of hydrogen-bonded and nonhydrogen-bonded chemicals. The great difference in melting and boiling points is clearly indicated. The kinetic energy required to melt a substance or to bring a liquid up to its normal boiling point is much greater for hydrogen-bonded compounds. This is due to intermolecular hydrogen bonds, which hold the molecules together.
Shape Selective Catalysis
Published in Subhash Bhatia, Zeolite Catalysis: Principles and Applications, 2020
Reactivities, diffusivities, and most other properties of homologous series usually change monotonously with the length of the molecule. Certain molecules in some molecular sieves do not obey this rule, i.e., their reactivity and diffusion behavior differ from those of their neighbors in the homologous series. This is the cage or window effect. Although this effect was observed in many different zeolites (chabazite, g-melinite), the most important studies involved erionite and the closely related zeolite KT.
Origin and Composition
Published in Mark J. Kaiser, Arno de Klerk, James H. Gary, Glenn E. Hwerk, Petroleum Refining, 2019
Mark J. Kaiser, Arno de Klerk, James H. Gary, Glenn E. Hwerk
A family of organic chemicals is known as a homologous series. Members of a homologous series have similar molecular structures and have graded physical properties that differ from one another according to the number of carbon atoms in the structure.
Liquid crystals for IR: Part I – synthesis and properties of perfluoroalkyl or perfluoroalkoxy terminated oligophenyls
Published in Liquid Crystals, 2020
Piotr Harmata, Jakub Herman, Przemysław Kula
One of the most important molecular structure elements influencing the mesomorphic behaviour is the length of the aliphatic chain [1]. Its variation, from the beginning of LC study, was the easiest molecular way of controlling the self-organising abilities of mesogenic materials [2]. The notion of comparing various properties (mesomorphic, optical, electrical) of homologous series members is well-established methodology of accumulating the knowledge related to structure–properties correlation. The beginners of liquid-crystalline chemistry very easily recognise the strong odd–even effect of the length of terminal chain or chains on mesomorphic properties and that for very first homologous members the mesomorphism is usually not present or if present, the melting temperature is extremely high often higher than clearing point [3]. Analysis of the IR properties of typical rod-like liquid-crystalline materials brings us information that flexible chains (necessary from the mesomorphic point of view) are responsible for very abundant absorption bands that are present at 3–3.5 µm and its harmonics is located in NIR at 1.71–1.76 µm [4]. To overcome these problems, several solutions have been proposed in the literature. All of them are related to shifting the parasitic absorption bands towards longer wavelength by incorporating heavier substituents like deuterium or fluorine [5,6]. The difference in mass between deuterium and fluorine strongly affects the absorption bands of fluorinated materials than those of hydrogen deuterium exchange [7]. The fundamental vibration of aliphatic C–F bond is observed at 7.68–8.65 µm, while the fundamental vibration of C–D bond is observed at 4.8 µm. Hence, the shift observed for H–F change is ~4.3 µm, while for H–D is 1.4 µm. The spectral benefits of using fluorine as a replacement of hydrogen are not in accordance with other properties that are much strongly affected by heavy fluorination than the one observed for deuteration. In addition, the synthetic chemistry of fluoroorganic compounds is much different from ‘conventional’ hydrocarbon-based organic materials. The effect of fluorination of the molecule on mesomorphic properties has been intensively studied in many review papers [8,9]. The general conclusion, being also the starting point of this work, states that increasing the level of fluorination is deteriorating the mesophase formation [10]. Based on such boundary conditions, 8 years ago we initiated research of finding the molecular design approach that can lead to the nematic phase formation. We assumed that molecules designed with structural limitations given below must appear with nematic properties: The terminal chain(s) do not contain any C–H bonds.The core system does not contain any C(sp3)-H systems.The polar substituents of the molecular core are limited to F or Cl or its derivatives.The linking units do not contain carbonyl group.