Chemical formulae, some conventions

How, indeed, should one interpret the symbols in a molecular formula Dalton thought that each of the symbols in his formulas must signify an actual "atom," in the sense of an absolutely unsplittable entity, much like an invisibly small but very real billiard ball— which is why he chose to represent his atoms by distinctive iconic circles, or spherical wooden models. Few chemists thereafter took such an unre-flectively realist position. At the other extreme, some regarded chemical formulas purely conventionally, as a mere aid to memory in representing the empirical facts of chemical analysis and having no real referent in the microworld at all. 

Bond density surfaces are also superior to conventional models when it comes to describing chemical reactions. Chemical reactions can involve many changes in chemical bonding, and conventional formulas are not sufficiently flexible to describe what happens (conventional plastic models are even worse). For example, heating ethyl formate to high temperatures causes this molecule to fragment into two new molecules, formic acid and ethene. A conventional formula can show which bonds are affected by the reaction, but it cannot tell us if these changes occur all at once, sequentially, or in some other fashion. 

Introduction. Etinol (chemical formula see below) is an important intermediate in the production of vitamins and food dyes, and is produced in a major plant. By using the conventional synthesis route, the raw material consumption of the presented intermediate step is very high, and the by-products formed pollute environmental compartments such as water and air. To produce 1 kg etinol in a multipurpose apparatus, ca. 3 kg raw material is required, so that ca. two-thirds of the raw materials are lost as waste, some in chemically changed form. This situation is unsatis ctory both ecologically and economically. 

In conventional organic nomenclature, a polymer is not considered to be an isomer of the repeating molecular unit, because the molecular formulas formally differ. This is a somewhat arbitrary distinction, however, because it is never really an isolated, single molecule of monomer that is compared with the polymer. In an aggregate of monomer molecules, intermolecular forces exist and the constitutional difference from an aggregate of polymer molecules is simply that some intermolecular forces have been converted into true chemical bonds. In any case, the term polymerization isomerism has had a long-standing use in coordination chemistry. It may refer... 

The acyclic aliphatic hydrocarbons have the general formula CnH2n + 2 cyclic saturated hydrocarbons (alicyclic hydrocarbons) have the general formula CnH2n (if monocyclic), CnH2n 2 (if bicyclic), etc. The structures of these hydrocarbons may be represented in the chemical literature in various ways some common conventions which are used freely in texts are illustrated here. 

A similar case would be where chemist A conceived a structural formula for a new compound but had trouble making it by the conventional chemical processes which first occurred to those skilled in the art. Chemist B following some nonobvious process steps does make the compound. Again one would be no place without the other, and this is a proper joint invention. A court has considered an analogous type of situation (26) and said that when one can perceive the crude form of elements or possibility of adaption to accomplish a result, he becomes a joint inventor with the one who actually does accomplish it. 

In principle, the conventions used for nonelectrolyte solutions developed in Chap. 11 could be employed for electrolyte solutions which are subject to the condition of electroneutrality. Agreement with experimental data could be obtained by choosing the molecular weight to be some fraction of the formula weight. However, these conventions generally lead to activity coefficients which are rapidly varying functions of composition. In order to avoid this, we formally define chemical potentials and activity coefficients for ionic components. The definition of chemical potentials for ionic components does not have operational significance since their concentrations cannot be varied independently. 

We will now discuss at some length the many ways in which deviations from standard bonding parameters lead to energetic destabilization of a molecule. We will focus on "stable" structures (i.e., not on reactive intermediates), but the notions we develop here also apply to reactive intermediates. We first explore acyclic systems, wherein molecular motions directly lead to strained forms. Note that we are not yet considering conventional chemical reactivity. We will be considering conformers, or conformational isomers. Recall that conformers are stereoisomers that interconvert by rotation around single bonds (see Chapter 6 for definitions of stereochemical concepts). These isomers are not to be confused with constitutional isomers, where the molecular formula is the same, but the atoms are arranged differently. 

From Figure 10.32 we can see how the structure of an ester is huilt up. However, it is more conventional to draw the condensed or full structural formulas of esters the other way round. Thus, ethyl ethanoate is usually written CH3COOC2H5 in chemical equations, for instance. Figure 10.33 shows the structures of some esters (propyl methanoate, methyl ethanoate and ethyl propanoate) written or drawn in this more usual format. 

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