Simple molecular compounds, physical properties

The characteristic property of these simple molecular compounds, which may be grouped under the name of onium compounds, is the fact that the atoms or groups combined directly with the onium forming or central element, act as a unit with the central atom in many physical and chemical transformations and are often termed... 

Compounds whose molecular compositions are multiples of a simple stoichiometry are polymers, stricdy, only if they are formed by repetition of the simplest unit. However, the name polymerization isomerism is applied rather loosely to cases where the same stoichiometry is retained but where the molecular arrangements are different. The stoichiometry PtCl2(NH3)2 applies to the 3 known compounds, [Pt(NH3)4][PtCU], [Pt(NH3)4][PtCl3(NH3)]2, and [PtCl(NH3)3]2[PtCl4] (in addition to the cis and trans isomers of monomeric [PtCl2(NH3)2]). There are actually 7 known compounds with the stoichiometry Co(NH3)3(N02)3. Again it is clear that considerable differences are to be expected in the chemical properties and in physical properties such as conductivity. 

Although many of the aromatic compounds based on benzene have pleasant odors, they are usually toxic, and some are carcinogenic. Volatile aromatic hydrocarbons are highly flammable and burn with a luminous, sooty flame. The effects of molecular size (in simple arenes as well as in substituted aromatics) and of molecular symmetry (e.g., xylene isomers) are noticeable in physical properties [48, p. 212 49, p. 375 50, p. 41]. Since the hybrid bonds of benzene rings are as stable as the single bonds in alkanes, aromatic compounds can participate in chemical reactions without disrupting the ring structure. 

Introduction to organic chemistry hydrocarbons and functional groups (structure, nomenclature, chemical properties). Physical and chemical properties of simple organic compounds should also be included as exemplary material for the study of other areas such as bonding, equilibria involving weak acids, kinetics, colligative properties, and stoichiometric determinations of empirical and molecular formulas. 

The first-order molecular connectivity index has been used very extensively in various QSPR and QSAR studies [269, 272, 273]. Thus, the question of its physical meaning has been raised many times. It has been found, in several studies [103, 178-180, 266, 274, 275], that this particular index correlates extremely well with the molecular surface area. It seems this index is a simple and very accurate measure of molecular surface for various classes of compounds and consequently correlates nicely with the majority of molecular surface dependent properties and processes. 

The simple physical properties of the given substance are compared with the same properties of known pure compounds of the same molecular formula. If adequate matching can be made of the freezing point, refractive index, and density of the given substance with a known pure compound of the same molecular formula, the identification may be considered substantially complete. 

Chemical Properties. Simple molecular-orbital theory predicts that many organometallic molecules should show electronic effects similar to conjugated systems, since the electronic structure is generally expressed in terms of molecular orbitals which involve both ring and metal orbitals. The ESR spectra (Sec. III.C) provide physical evidence for this formulation however correlation between chemical reactivities and theoretical quantities, such as charge densities and localization energies, which has been of use in aromatic systems (60) has not been attempted. Indeed, very few detailed kinetic studies of organometallic compounds have been reported with which to compare theory. We consider the different classes of compounds in turn. 

This review, which covers the literature up to mid-1968, presents the knowledge, which is available to date, concerning the molecular and electronic structure of pyrrole. It also surveys the spectroscopic and nonspectroscopic physical properties of pyrrole and its simple derivatives. During the past 25 years, as a result of developments and improvements in instrument design, the literature on the physicochemical properties of organic compounds has expanded rapidly. Mainly as a result of the instability or nonavailability of many compounds, however, the study of pyrroles has lagged somewhat behind... 

Contents Quantum Mechanics and Atomic Theory. - Simple Molecular Orbital Theory. -Structural Applications of Molecular Orbital Theory. - Electronic Spectra and Magnetic Properties of Inorganic Compounds. - Alternative Methods and Concepts. - Mechanism and Reactivity. - Descriptive Chemistry. - Physical and Spectroscopic Methods. - Appendices. -Subject Index. 

Besides forming molecular compounds with water (hydrates) certain salts have the property of combining with a second salt either with or without water. In these combinations the character of the individual salts is somewhat modified but not completely changed. Hence the name, double salts . In physical properties such as crystalline form, solubility, and, in some cases, color, the crystals of the double salt differ from those of the simple salts. These compounds follow the law of definite proportions. 

---