The Hill System

In most publications, including Chemical Abstracts and Beilstein, molecular formulae are given in Hill system order. For organic compounds, the order is C first, then H, and then the remaining element symbols alphabetically. For compounds that do not contain carbon, the element symbols are ordered alphabetically (see Hill, E. A., J. Am. Chem. Soc., 22, 478-490, 1900). 

Although the Hill system is now used almost exclusively, other systems have been used in the past. For example, the early formula indexes to Beilstein used the Richter system, in which the elements are cited in the order C, H, O, N, Cl, Br, I, F, S, R 

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The elements of an organic compound are listed in empirical formulas according to the Hill system [8] and the stoichiometry is indicated by index numbers. Hill positioned the carbon and the hydrogen atoms in the first and the second places, with heteroatoms following them in alphabetical order, e.g., C9H11NO2. However, it was recognized that different compounds could have the same empirical formula (see Section 2.8.2, on isomerism). Therefore, fine subdivisions of the empirical... 

A single unstable compound of known composition is placed in the main first volume and is located on the basis of its empirical molecular formula expressed in the Hill system used by Chemical Abstracts (C and H if present, then all other element symbols alphabetically). The use of this indexing basis permits a compound to be located if its structure can be drawn, irrespective of whether a valid name is known for it. A representation of the structure of each compound is given on the third bold title line while the name of the compound appears as the first bold title line. References to the information source are given, followed by a statement of the observed hazard, with any relevant explanation. Cross-reference to similar compounds, often in a group entry, completes the entry. See Trifluoroacetyl nitrite p. 244. 

STRAWBERRIES AND RASPBERRIES. These are the most demanding in terms of soil requirements. They should be grown only on medium-heavy to light, free-draining soils. Areas with compaction or waterlogging are unsuitable. Reduced yields and root disease problems are unavoidable on unfavourable soils. Planting by the hill system is to be recommended if soil conditions are not entirely optimal. 

The Formula Index links the molecular formulae of chemical substances with their CA Index Names, CAS registry numbers, and CA abstract numbers. Molecular formulae are arranged according to the Hill system order (see Section 10.1). 

The Hill system is used in modified form today by Chemical Abstracts and Referativny Zhurnal, Khimiya (17) and indexes both inorganic and organic compounds. Beilsteins Handbuch (2) formula index to the second supplement uses the Hill system. This index covers the original work and two supplements. 

Volumes 28 and 29 of the Second Supplement are, respectively, the subject and formula indexes to the entire "Beilsteins Handbuch the three-part cumulative formula index, arranged by the Hill system, is the only index recording the known formulas of organic compounds from the beginnings of organic chemistry through 1929. (The Chemical Abstracts cumulative formula index extends this period to 1946.)... 

In all tables, the species are arranged by the sum formula according to the Hill system (alphabetical order of element symbols except for species containing carbon in which case C followed by H precede the other elements). The tables contain the sum formula, the structure formula, a... 

Mixtures are entered in the main body of the bibliography in the alphabetical order of the first component according to the Hill system as employed by Chemical Abstracts. An index is provided so that all the binary mixtures involving a particular substance can be located. The literature has been covered to the end of 1974, with some 1975 publications also included. 

All the information of this voltrme is also stored on the CD-ROM in the attachment. In the printed version you have only access to stmctural iirformation by means of the gross formttla in the Hill system, whereas the electronic version offers several possibilities to access. 

Last but not least, entries can be retrieved by searching gross formula in the Hill system, where the element symbols and their index numbers are separated by no blanks at all, such as CaC12 for CaCl2 or C1FH2 for CIFH2. For more complex searches, please use the exclusive Online Help of the Acrobat... 

The molecular formula of a compound carries information only about the number of atoms contained in a molecule. For example, the molecular formula C2H 0 describes molecules made of two C atoms, six H atoms, and a single 0 atom. Usually C is listed first, followed by H, if any, and other element symbols in alphabetic order. This is termed the Hill system [128]. 

The present tome consists of two sections. The first section reviews the genins (1-420) and their 4-monomethyl (421-461) and 4,4-demethyl derivatives (462-472) in numerical order. The second section includes the glycosides (473-861). This section concludes with three glycosides of 4-monomethyl analogs (859-861). Each section is structured based on the Hill system order. 

The molecules are arranged according to the Hill system [OOHil]. This means that the moleeules are arranged in alphabehcal order of the element symbols except caibon atoms which are written first... 

The empirical formula is the molecular formula of a chemical compound. The order of atoms follows the Hill system which is utilized by the Chemical Abstracts Services and by the Beilstein Institute. Within the empirical formula C is the first element symbol, H is the second, the other element symbols are added in alphabetical order. The empirical formula does not take into account of any crystal water content. Using this field for searches requires that the above guidelines are strictly followed. 

The Hill System has been modified for several classes of substances (the following substances on the left are not mentioned in the Formula Index, they are to be found under the substance names on the right. Sect. 2.5) ... 

The rings are arranged according to their size, even in the elemental analysis. Rings of equal size are listed alphanumerically in the order of their molecular formula according to the Hill System. 

According to the Hill System, the molecular formula of the above-mentioned substance is C2Cl3Na02 (Sect. 2.1.3.3). However, it is not recorded under this molecular formula in the Formula Index. 

As explained in Sect. 2.1.3.3, molecular formulae are written according to the Hill System. The elements are written in the order first carbon and hydrogen followed by the other elements alphabetically. If the number of atoms is above 103 or if the formula is not defined precisely (e.g. bronze), the field MF will carry the indication unspecified. 

When the atoms are known, but the numeric values associated with each element are not, the field Element Formula (ELF) should be used for searching. Enter only element symbols and remember the rules of the Hill System. In any case, elements must be separated by blanks (Fig. 89). 

The compounds are arranged by their gross formulae according to the Hill system, i.e. by the increasing number of C and H atoms followed by the other atoms in alphabetieal order. 

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