The Girolami method,
named after Gregory Girolami, is a predictive method for estimating
densities of pure
liquid
A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, ...
components at
room temperature
Colloquially, "room temperature" is a range of air temperatures that most people prefer for indoor settings. It feels comfortable to a person when they are wearing typical indoor clothing. Human comfort can extend beyond this range depending on ...
. 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 a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the 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 held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
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 most commonly refers to:
* Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom
* Alcohol (drug), an intoxicant found in alcoholic drinks
Alcohol may also refer to:
Chemicals
* Ethanol, one of se ...
s)
* a carboxylic function (
Carboxylic acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...
s)
* a primary or secondary
amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...
function
* an
amide
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it i ...
group (incl. amides substituted at the
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at sevent ...
)
* 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. ...
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 crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromati ...
. 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
Compound may refer to:
Architecture and built environments
* Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall
** ...
) 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