Heteromolecular formation

Examples of crystalline associates where dimethyl sulfoxide is involved as one of the heteromolecular constituents are known in an appreciable number1. Certainly the associate between dimethyl sulfoxide and trimesic acid 84 (cf. Chapter 5 in Vol. 140 of this series) is one of the important individual cases. Characteristic modes of association between the carboxylic hosts discussed here and dimethyl sulfoxide are illustrated in Fig. 24. Pertinent geometry data are listed in Tables 17 and 18. One may realize from Fig. 24 that the fundamental mode of association of the host acids 20, 26, 37, and 41 is the formation of discrete H-bonded islands of host and (usually) one guest molecule. 

Roedel, W., Measurement of Sulfuric Acid Saturation Vapor Pressure Implications for Aerosol Formation by Heteromolecular Nucleation, J. Aerosol Sci., 10, 375-386 (1979). 

It is emphasized that the terms excimer2 and exciplex3,4 are reserved here for homomolecular and heteromolecular excited double molecules formed after the act of light absorption by one component in a process of photoassociation, in the absence of spectroscopic or cryoscopic evidence for molecular association in the ground state. Recent findings indicate that excimer (or exciplex) formation may also result from triplet-triplet annihilation,5,8 cation-anion combination7 (doublet-doublet-annihilation), and electron capture by the (relatively stable) dimer (or complex) cation8 these processes are discussed in Section VII. 

The heteromolecular production of particles in a vapor mixture is estimated from a model similar to the homogeneous case above. However, the production rate depends on the energy of formation of mixed embryos, the composition of which depends on the thermodynamic properties of the mixture. 

Elements of Group IV clusters. Investigation of C0-02 mixtures also revealed reactions between Ol and CO. The role of impurity reactions involving H20 is considered in detail and the implications of all data to the vapour-phase radiolysis of C02 are discussed.202 A wide range of heteromolecular clusters containing CO and/or C02 together with S02, NO, or H20 has been found in isentropically expanding jets 203 the observed clusters and their formation conditions are summarized in Table 12. These clusters, particularly the hydrates, are of importance in atmospheric chemistry since favourable conditions for their formation are known to be present in jet-aircraft exhausts.203... 

In some cases, rearrangement of bonds leads to formation of electro-neutral ionic associate in binary solvents where heteromolecular associates are formed ... 

In the overwhelming majority of cases, this acid-base interaction limits itself only to the first stage - formation of heteromolecular adduct. Interactions occurring in all stages of the scheme [9.13] are typical of binary solvents such as triethylene amine-pyridine or N-diethylaniline. Proton-donor function towards the amine component reveals itself distinctly in the case of diphenylamine. 

Interaction is accompanied by formation of the heteromolecular associates. It can be demonstrated by analysis of volumetric equations for the liquid mixed systems, data on volume compression, i.e., positive density deviation from additivity rule, and hence negative deviations of experimental specific molar volume from partial molar volume additivity rule. 

In universal media formed by two solvate-inert solvents aceording to equation [9.53a], equilibrium eonstants of the process of heteromolecular adduct formation depend exponentially on reciprocal permittivity thus... 

Let us consider the effect of specific solvation on equilibrium eonstant of the heteromolecular association process as an example of assoeiate formation with a simplest stoichiometry ... 

The process of heteromolecular association [9.64] is due to displacement of the solvent components and formation of completely or partially desolvated adduct ... 

Low eonstant of the ion associate formation process of triphenylehloromethane, high constant of the ion assoeiation proeess, and low constant of the heteromolecular association process of HCI (HCI solutions in listed solvents obey the Henry s Law) show that only methanol is an associative partieipant of the equilibrium. 

Homogeneous nucleation is the formation of the condensed phase (particles) from purely gaseous molecules. If only a single molecular species is involved, the process is termed homomolecular, while it is called heteromolecular when more than one such species participates. Aspects of homogeneous nucleation depend to a great extent upon collision rates this leads to highly mixed results upon treatment by kinetic theoretic means. Undoubtedly, any ultimate description will necessitate details not only of kinetics but also of dynamics and microparticle microphysics to account for the rates and structure of critical (i.e., stable) cluster formation. 

Thus for Kef calculation one must obtain the equilibrium constant of processes [9.71] - K s, [9.69] - Kea and [9.70] - Kpg from conductance measurements. The constant Kef is identified in literature as calculated by taking into account the specific solvation . The value Kef characterizes only the universal solvation effect on the process of heteromolecular associate formation. The approach cited above can be illustrated by equilibrium ... 

The four adamantane derivatives, 2-hydroxyadamantane, 2-adamantanone, 2-adamantanone oxime and 2-adamantanecarboxylic acid (Formula 5.4) all have a nearly spherical shape. Screening experiments were performed with each possible pair of the four compounds, but only two co-crystals were found hydroxyadamantane- adamantanone and adamantanone oxime-adamantane-carboxylic acid. The alcohol-ketone and acid-oxime hydrogen bonds provide strong supramolecular synthons for the formation of these co-crystals, while for the other combinations possible heteromolecular synthons are not preferred to homomolecular ones. The results thus show that shape similarity cannot overcome the effect of good homomolecular synthons. 

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