Polarity and chemical reactivity

P. Brunero, J. P. Fouassier, and J. Faure, J. Chim. Phys. Phys.-Chim. Biol. 79, 343 (1982). [294] C. Reichardt Empirical Parameters of Solvent Polarity and Chemical Reactivity, in Ft. Ratajczak and W. J. Orville-Thomas (eds.) Molecular Interactions, Wiley, Chichester, 1982, Vol. 3, Chapter 5, p. 241ff. [295] H. Langhals, Angew. Chem. 94, 739 (1982) Angew. Chem. Int. Ed. Engl. 21, 724... 

Despite a similar molecular structure, these three organic compounds present significant differences in terms of polarity and chemical reactivity and therefore the study of their interactions with the air—water interface, and the possible atmospheric implications, is interesting. Indeed, methyl chloride and methanol at the liquid water-vapor interface have heen the subject of previous theoretical and experimental investigations [57-60], which focused on the preferred orientations and the thermodynamics of the adsorption process. In the present work, we have carried out QM/MM MD simulations for methyl chloride, acetonitrile, and methanol trying to get further insights into the solvation effects of the interface on the electronic properties of the systems, as well as on the orientafional dynamics. 

C. Reichardt, Empirical Parameters of Solvent Polarity and Chemical Reactivity, in H. Ratajczak and W. J. Orville-Thomas, Eds., Molecular Interactions, Vol. 3, Wiley, Chichester 1982, p. 241. 

The opening paragraph of this chapter emphasized that the connection between structure and properties is what chemistry is all about We have just seen one such con nection From the Lewis structure of a molecule we can use electronegativity to tell us about the polarity of bonds and combine that with VSEPR to predict whether the mol ecule has a dipole moment In the next several sections we 11 see a connection between structure and chemical reactivity as we review acids and bases... 

Mesomerism involving polarized and nonpolarized contributing enamine forms influences the enamine s spectral properties and chemical reactivity. For mesomerism to be present, a planar arrangement is required for the three atoms of enamine grouping and the five atoms immediately bound to this system. If this condition is not fulfilled, full interaction of the tt electrons of the double bond with the free electron pair on the nitrogen atom is impossible. Enamines in which mesomerism is inhibited do not show the properties characteristic of enamines, and only the mutual electrostatic interaction of the double bond and lone electron pair of the nitrogen atom can be observed. Such steric hindrance of mesomerism occurs mainly in polycyclic systems. 

The substitution of a polar component with another one can improve or decrease selectivity because of the change of interactions in the chromatographic system. This can be based on the namre and chemical reactivity of the solute. 

This chapter aims to present the fundamental formal and exact relations between polarizabilities and other DFT descriptors and is organized as follows. For pedagogical reasons, we present first the polarizability responses for simple models in Section 24.2. In particular, we introduce a new concept the dipole atomic hardnesses (Equation 24.20). The relationship between polarizability and chemical reactivity is described in Section 24.3. In this section, we clarify the relationship between the different Fukui functions and the polarizabilities, we introduce new concepts as, for instance, the polarization Fukui function, and the interacting Fukui function and their corresponding hardnesses. The formulation of the local softness for a fragment in a molecule and its relation to polarization is also reviewed in detail. Generalization of the polarizability and chemical responses to an arbitrary perturbation order is summarized in Section 24.4. 

Chemists commonly include formal charges as part of structural formulas. While such a practice might be viewed simply as chemical bookkeeping , it serves as well to anticipate molecular properties and chemical reactivity. However useful charges may be, the fact is that they may neither be determined from any experiment nor calculated in a unique manner. (Discussion of why this is so is provided in Chapter 16.) The closest one can get is a measure of overall molecular polarity as contained in the dipole moment. This is a measurable and calculable quantity. ... 

One of us has used molecular polarization potentials (MPP) to study the interaction of aromatic molecules, including furan, thiophene, and pyridine with a positive unitary charge, these maps being powerful tools for the study of intermolecular interactions and chemical reactivity [129,130], This kind of study leads us to examine theoretically the problem of the interaction between cations and anions with aromatic rings. We were pioneers in proposing that, in parallel with cation-7i-systems (for instance, benzene), there should exists anion-perfhiorinated-7i-systems (for instance, hexafluorobenzene) [131]. These studies include tetrafluorofuran and tetrafluorothiophene (128, 129). Simultaneously, Mascal et al. [132] described the same phenomenon but with 1,3,5-triazine (130) and 2,4,6-trifluoro-l,3,5-triazine (131) as acid 7i-systems. The group of the University of Palma de Mallorca has published a large number of papers on this topic [133] that are well summarized in a two recent reviews [134,135],... 

The above mentioned mesomerism between a polarized and a nonpolarized structure of enamines possessing a tertiary nitrogen atom is reflected in their physical properties and chemical reactivity. For... 

The physical and chemical properties of analytes and the nature of the sample have a major impact on, and often limit, the sampling and other procedures and techniques that can be employed in an analytical method. Major issues that must be considered when developing an analytical method are the volatilities, thermal stabilities, photochemical stabilities, polarities, water solubilities, and chemical reactivities of the sample components or target analytes the physical state of the sample and the nature of the sample matrix. Analytes, whether organic or inorganic, can be broadly divided into three categories based partly on vapor pressure, or volatility, at ambient temperature and on some other physical and chemical properties. There are major differences in the procedures and techniques used to acquire and process condensed-phase and vapor-phase samples. 

The physical properties and chemical reactivity of molecules may be and often are drastically changed by a surrounding medium. In many cases specific complexes are formed between the solvent and solute molecules whereas in other cases only the non-bonded intermolecular interactions are responsible for the solvational effects. By one definition, the environmental effects can be divided into two principally different types, i.e. to the static and dynamic effects. The former are caused by the coulombic, exchange, electronic polarization and correlation interactions between two or more molecular species at fixed (close) distances and relative orientation in space. The dynamic interactions are due to the orientational relaxation and atomic polarization effects, which can be accounted for rigorously only by using time-dependent quantum theory. 

Optical isomers are nonsuperimposable mirror images. ( Superimposable means that if one structure is laid over the other, the positions of all the atoms will match.) Like geometric isomers, optical isomers come in pairs. However, the optical isomers of a compound have identical physical and chemical properties, such as melting point, boiling point, dipole moment, and chemical reactivity toward molecules that are not optical isomers themselves. Optical isomers differ from each other in their interactions with plane-polarized light, as we will see. 

Alkorta I, Perez JJ, Villar HO. Molecular polarization maps as a tool for studies of intermolecular interactions and chemical reactivity. J Mol Graph 1994 12 3-13. 

When inorganic fillers and fibers are dispersed in an organic polymer matrix, the interface is weakened by sharp differences in modulus, thermal expansion, polarity, chemical attraction, and chemical reactivity. This gives rise to many practical problems as listed below ... 

Whereas methyl transfer reactions proceed faster in nonpolar media, the Menschutkin (Sn2) reaction (CH3CH2)3N + CH3CH2I —> (CH3CH2)4N+ + T proceeds faster in polar media. Variations in nt upon a change on solvent polarity control chemical reactivity in methyl transfers, whereas for the above mentioned Sn2 displacement the significant changes of AG ovCTCome the effect of nt and dominate the variations on AG. ... 

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