Procedure
The method uses purely additive volume contributions for single atoms and additional correction factors for components with special functional groups which cause a volume contraction and therefore a higher density. The Girolami method can be described as a mixture of an atom and group contribution method.Atom contributions
The method uses the following contributions for the different atoms: A scaled molecular volume is calculated by : and the density is derived by : with the molecular weight M. The scaling factor 5 is used to obtain the density in g·cm−3.Group contribution
For some components Girolami found smaller volumes and higher densities than calculated solely by the atom contributions. For components with * a hydroxylic function (Alcohol (chemistry), Alcohols) * a carboxylic function (Carboxylic acids) * a primary or secondary amine function * an amide group (incl. amides substituted at the nitrogen) * a sulfoxide group * a sulfone group * a ring (non-condensed), it is sufficient to add 10% to the density obtained by the main equation. For sulfone groups it is necessary to use this factor twice (20%). Another specific case are condensed ring systems like Naphthalene. The density has to increased by 7.5% for every ring; for Naphthalene the resulting factor would be 15%. If multiple corrections are needed their factors have to be added but not over 130% in total.Example calculation
Quality
The author has given a mean quadratic error (RMS) of 0.049 g·cm−3 for 166 checked components. Only for two components (acetonitrile and dibromochloromethane) has an error greater than 0.1 g·cm −3 been found.References
External links