The Girolami method,
named after Gregory Girolami, is a predictive method for estimating
densities of pure
liquid
Liquid is a state of matter with a definite volume but no fixed shape. Liquids adapt to the shape of their container and are nearly incompressible, maintaining their volume even under pressure. The density of a liquid is usually close to th ...
components at
room temperature
Room temperature, colloquially, denotes the range of air temperatures most people find comfortable indoors while dressed in typical clothing. Comfortable temperatures can be extended beyond this range depending on humidity, air circulation, and ...
. The objective of this method is the simple prediction of the density and not high precision.
Procedure
The method uses purely additive volume contributions for single atoms and additional correction factors for components with special
functional group
In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...
s 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
A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
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
Alcohol may refer to:
Common uses
* Alcohol (chemistry), a class of compounds
* Ethanol, one of several alcohols, commonly known as alcohol in everyday life
** Alcohol (drug), intoxicant found in alcoholic beverages
** Alcoholic beverage, an alco ...
s)
* a carboxylic function (
Carboxylic acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...
s)
* a primary or secondary
amine
In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...
function
* an
amide
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a chemical compound, compound with the general formula , where R, R', and R″ represent any group, typically organyl functional group, groups or hydrogen at ...
group (incl. amides substituted at the
nitrogen
Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
)
* a
sulfoxide
In organic chemistry, a sulfoxide, also called a sulphoxide, is an organosulfur compound containing a sulfinyl () functional group attached to two carbon atoms. It is a polar functional group. Sulfoxides are oxidized derivatives of sulfides. E ...
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
Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, and is a white Crystal, crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 Parts-per notation ...
. 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
Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not class ...
and
dibromochloromethane
Dibromochloromethane is a colorless to yellow, heavy and nonflammable compound with formula . It is a trihalomethane.
The substance has a sweet odour. Small quantities of dibromochloromethane are produced in ocean by algae.
Applications
Dibrom ...
) has an error greater than 0.1 g·cm
−3 been found.
References
External links
Online calculator for the Girolami model
{{DEFAULTSORT:Girolami Method
Thermodynamic models