The molar volumes (Vm) of organic compounds present in the modelled system are needed to calculate aerosol size and density. On this page a simple structure-based method (G. S. Girolami J. Chem. Educ. 71, 962-964, 1994) is used to estimate Vm and densities of pure liquid organic compounds at 298.15 K.
Values of the molar volumes obtained here, or from other sources, can be entered on the properties page for the organic compound of interest.
Fill in the form below (blanks will be treated as zero), and press the Submit button.
Accuracy: Girolami tested the method against data for 166 liquid organic compounds, and found an rms error of 0.049 g cm-3. In only two cases did the error exceed 0.1 g cm-3.
Unfused rings: the number of separate rings of carbon atoms present in the molecule. These rings are distinct, and do not have atoms in common. Examples: benzene and cyclohexanol each have one unfused ring, whereas dicyclohexanol has two.
Fused rings: the number of carbon rings present in the molecule which share atoms. Examples: naphthalene and its derivatives have two fused rings, and anthracene has three.
The effect of ring structures is to increase density by 10% (per unfused ring) and 7.5% (per fused ring). The maximum increase, including that due to the functional groups in section 2, is limited to 15% overall.
The influence of more complex bridged structures, such as are found in some of the terpenes, have not been investigated with the model. Users should apply reasonable interpretations of the "unfused" and "fused" definitions above to obtain upper and lower limits on the estimated density and molar volume.
Amides: both primary amides such as acetamide (containing an –NH2 group attached to a carbonyl group), and N-substituted amides such as N-phenyl acetamide in which one or both of the hydrogen atoms attached to the N atom is replaced by a carbon chain or a functional group.
Sulphoxides and sulphones: these groups consist of oxygen atom(s) double bonded to a sulphur atom.
Amino: both primary (R–NH2) and secondary (R1–NH–R2) amino groups.
Cyclohexanol, C6H12O: one unfused ring, and one –OH group (estimated density = 0.92 g cm-3, true density = 0.962 g cm-3); ethylenediamine, C2H8N2: two primary amine groups (estimated density = 0.90 g cm-3, true density = 0.899 g cm-3); sulpholane, C4H8O2S: one unfused ring, and one >SO2 (sulphone) bond (estimated density = 1.30 g cm-3, true density = 1.262 g cm-3); 1-bromonaphthalene, C10H7Br: two fused rings (estimated density = 1.49 g cm-3, true density = 1.483 g cm-3).