Hill system
The Hill system (also called Hill's system ) is a rule that defines the order of the element symbols in chemical formulas . The Hill system was filed with the U.S. Patent Office by Edwin A. Hill in 1900.
definition
The molecular formula of a compound is written in the order C , H and then all the other elements in alphabetical order. In the case of compounds without carbon, the order is strictly alphabetical, the hydrogen is then classified. Isotope abbreviations such as D and T are treated like separate elements and sorted accordingly.
Sorting of sum formulas
For a lexicographical sequence , the atomic frequencies are to be sorted numerically in ascending order (C1, ..., C9, C10, ... instead of C1, C10, ..., C2, ...). The Hill system is used by leading scientific literature databases and referencing substance or reaction indices (e.g. Chemical Abstracts , Beilstein from 1958) as a ranking aid for the formula registers.
Examples
BH 3 , BaCl 2 , CH 4 , CHNaO 3 , ClNa, C 2 H 4 , C 2 H 4 O 2 , C 2 H 6 , HOT
Not to be confused with the sum formulas according to the Hill system are the semi-structural formulas that are also frequently used . For example, the Hill formula for methanol is CH 4 O, while the semi-structural formula is CH 3 OH. In this example, in the semi-structural formula, the OH group that is characteristic of alcohols is more obvious.
literature
- Edwin A. Hill: On A System Of Indexing Chemical Literature; Adopted By The Classification Division Of The US Patent Office . J. Am. Chem. Soc. 1900 , 22 (8), 478-494, doi : 10.1021 / ja02046a005