General molecular formula
General empirical formulas are mainly used in organic chemistry to indicate the number of atoms in a molecule or the number ratio between the types of atoms of the homologous series of chemical compounds . The sum formulas of the individual compounds can be determined from the general sum formulas .
Example:
A butane molecule from the homologous series of alkanes has four carbon atoms ( n = 4). The general formula for alkanes is C n H 2 n +2 . The number of hydrogen atoms then results from
The molecular formula of butane is therefore C 4 H 10 .
In the case of compounds whose functional groups have a carbon atom and which are explicitly specified, n in the empirical formula is to be reduced by 1 for each functional group that contains a carbon atom. A molecule of butanoic acid (butyric acid) from the homologous series of alkanoic acids with the general empirical formula C n H 2 n +1 COOH with n = 3 has 4 carbon atoms, one of which is in the carboxy group (-COOH). From this follows the empirical formula of butanoic acid C 3 H 7 COOH.
General empirical formulas of homologous series
- Alkanes : C n H 2 n +2 ( n = 1, 2, 3, 4, ...)
- Alkenes : C n H 2 n ( n = 2, 3, 4, ...)
- Alkynes : C n H 2 n −2 ( n = 2, 3, 4, ...)
- monovalent alkanols : C n H 2 n +1 OH ( n = 1, 2, 3, 4, ...)
- monovalent alkanals : C n H 2 n +1 CHO ( n = 0, 1, 2, 3, 4, ...)
- monovalent alkanoic acids : C n H 2 n +1 COOH ( n = 0, 1, 2, 3, 4, ...)
More general sum formulas
- Cycloalkanes : C n H 2 n +2 (1− x ) ( x is the number of rings)
- Simple sugars (monosaccharides): C n H 2 n O n [Exceptions: deoxy sugars (e.g. deoxyribose , C 5 H 10 O 4 )]
- Double sugars (disaccharides): C n H 2 n −2 O n −1
- Arsane : As n H 2 n +2
- Boranes : B n H m ( n , m = integer)
- Teutons : Ge n H 2 n +2
- Silicas (ring-shaped): [Si (OH) 2 –O–] n
- Silanes : Si n H 2 n +2
See also
Individual evidence
- ^ A b Jürgen Schatz, Robert Tammer: First Aid - Chemistry and Physics for Physicians . Springer-Verlag, 2015, ISBN 978-3-662-44111-4 , pp. 455 ( Google Books ).