Classification and Nomenclature

3 Key excerpts on "Classification and Nomenclature"

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  eBook - ePub

  Chemical Graph Theory

  Introduction and Fundamentals

  • D Bonchev(Author)
  • 2018(Publication Date)
  • Routledge

    (Publisher)

  These methods include nomenclatures, notations, connection tables, adjacency matrices, molecular formulas, and fragment codes [ 1, 2 ]. The term “nomenclature” is sometimes used as a generic term to include not only nomenclatures but also notations and connection tables. Since reference is made in this chapter to nomenclatures and notations, it is useful to define them here and to distinguish them from connection tables (see Figure 1). Nomenclature is defined [ 3 a] as: “a system or set of names or designations used in a particular science, discipline, or art and formally adopted or sanctioned by the usage of its practitioners.” Chemical nomenclature is more specifically defined as: “a set of chemical names that may be systematic … or not and that aims to tell the composition and often the structure of a given compound by naming the elements, groups, radicals, or ions present and employing suffixes denoting function …, prefixes denoting composition …, configuration prefixes …, operational prefixes …, arabic numbers or Greek letters for indicating structure (as positions of substituents), or Roman numerals for indicating oxidation state.” Chemical nomenclature is illustrated in Figure 1 with reference to the chemical structure diagram mentioned above

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  eBook - ePub

  Organic Chemist's Desk Reference

  • Caroline Cooper, Rupert Purchase(Authors)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  3 Nomenclature Fundamentals

  3.1 INTRODUCTION

  This and the following chapter are intended as a quick reference guide, and should not replace the International Union of Pure and Applied Chemistry (IUPAC) publications for definitive guidance nor the Chemical Abstracts Service (CAS) 2007 documentation for a full description of the current CAS nomenclature system.

  Naming compounds accurately is important for publication, and the mainstream chemical journals require systematic nomenclature of new compounds. However, a compound may have several equally valid names, and a name intelligible to a fellow organic chemist may not be appropriate for publication in, for example, fire regulations. The function of nomenclature is to provide an acceptable name for a given compound in a particular context.

  Substructure searching is now used extensively for the indexing and location of known substances. For many purposes, it is sufficient to be able to recognise from the name that the correct compound has been tracked down as a result of searching by substructure, molecular formula and so on.

  Before publication, all available information on products should be checked to make sure a compound being reported is in fact new. For synthetic compounds, a structure search can be carried out against Chemical Abstracts and Reaxys (see Sections 1.1.1 and 1.1.2 ).

  For newly isolated natural products, Dictionary of Natural Products is the best source (Section 1.2.1 ). Duplicating trivial names when reporting new natural products is to be avoided. Names should be checked against the Dictionary of Natural Products or CAS.

  Nomenclature algorithms are available to generate names from structure drawing programs (see Section 3.9 ).

  FURTHER READING

  Fox, R. B. and Powell, W. H., Nomenclature of Organic Compounds, Principles and Practice

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  Philosophy of Chemistry

  • Dov M. Gabbay, Paul Thagard, John Woods(Authors)
  • 2011(Publication Date)
  • North Holland

    (Publisher)

  There is a further distinction between chemical equations and laws of physics, to do with the meaning of the notations. In physics, for the most part, ‘+’ and ‘=’ are to be read numerically. In chemistry the very same sign forms mean something quite different. ‘+’ means something like ‘reacting’, while ‘=’ means ‘gives rise to’ or something like that. Of course, as Benjamin Brodie pointed out, every chemical equation is accompanied by a ghostly sibling, in which the atomic weights of the elements are inserted. Then the meanings of the notation change radically. Juxtaposing letters in a chemical formula means ‘combined with’. Juxtaposing letters in the gravimetric equation means ‘add’.

  4. Chemical Taxonomies

  By mid-eighteenth century a firm distinction between elements and compounds had grown up. There were disagreements about the scope of these broad generic categories. Were ‘light’ and ‘heat’ chemical elements like ‘hydrogen’ and ‘sulphur’? However, the distinction was not called into question. Much as Linnaeus built the dual taxonomies of animals and plants, so nineteenth century chemists were much occupied with classification systems for elements and for compounds. The former led to the periodic table while the latter led to the nomenclature we still use for describing compounds in terms of their constituent elements (or radicals) and the proportions with which they are combined in the compound in question.

  Do we find another kind of law-like statement in the discourses with which the periodic table is described and its arrangements explained? The role of nominal and real essences, and so of theory in the analysis of the principles of such classifications have been much discussed in recent literature [Harré, 2005 , 7-30]. For the moment let us shelve the question of how real and nominal essence definitions are related. At this point it will be helpful to introduce a working distinction between the chemical properties of a substance and its physical properties. Chemical properties are those germane to procedures of substance transformation, except those brought about by radioactivity, natural or induced. Physical properties include observable attributes germane to producing changes of state, and importantly for the context of this chapter, those which are used in the setting up of the explanatory regresses which underpin our knowledge of chemical transformations.

  The Wikipedia (such a useful source!) offers the following account of Manganese. It is a ‘gray-white metal, resembling iron. It is a hard metal and very brittle, fusible with difficulty’. So far this is a list of physical properties, germane to such changes of state as liquifaction. Wikipedia then goes to add that it is easily oxidised, and ‘sulfur-fixing, deoxidizing, and alloying’. These are chemical properties, according to the above distinction, that is germane to the transformation of substances, for example iron into steel. Potassium permanganate (Condy's crystals) was well known in my childhood for its anti-bacterial properties.

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