F number (chemistry) explained

F number is a correlation number used in the analysis of polycyclic aromatic hydrocarbons (PAHs) as a descriptor of their hydrophobicity and molecular size.^[1] It was proposed by Robert Hurtubise and co-workers in 1977.^[2]

Calculation

The F number is calculated using the formula:

F=B₂+C₁₂-

	1
	2

where:

B₂ is the number of double bonds

C₁₂ is the number of primary carbon and secondary carbon atoms

R is the number of non-aromatic rings.

Example

For fluorene, there are 6 apparent double bonds (three pi bonds in each side benzene-like ring); the central ring has one secondary carbon and is non-aromatic. Therefore:

F=6+1-

	1
	2

1=6.5

Correlation

It has been found that the F number linearly correlates with the log k' value (logarithm of the retention factor) in aqueous reversed-phase liquid chromatography. This relationship can be used to understand the significance of different aspects of molecular architecture on their separation using different stationary phases.^[3] This size analysis is complementary to the length-to-breadth (L/B) ratio, which classifies molecules according to their "rodlike" or "squarelike" shape.^[4]

External links

List of F numbers for PAHs

Notes and References

Jinno . Kiyokatsu . Okamoto . Mitsuyoshi . . 1984 . 18 . 9 . 495–498 . Molecular-shape recognition of polycyclic aromatic hydrocarbons in reversed phase liquid chromatography . 10.1007/BF02267234 . 98307769 .
John F. . Schabron . Robert J. . Hurtubise . Howard F. . Silver . . 49 . 14 . 2253–2260 . 1977 . Separation of hydroaromatics and polycyclic aromatic hydrocarbons and determination of tetralin and naphthalene in coal-derived solvents . 10.1021/ac50022a037 .
Jinno . Kiyokatsu . Okamoto . Mitsuyoshi . . 1984 . 18 . 1 . 44–46 . Correlation of the retention data of polyaromatic hydrocarbons obtained on various stationary phases used in normal- and reversed-phase liquid chromatography . 10.1007/BF02279465 . 54035024 .
Molecular Shape Selectivity through Multiple Carbonyl−π Interactions with Noncrystalline Solid Phase for RP-HPLC . M. Mizanur . Rahman . Makoto . Takafuji . Hamid R. . Ansarian . Hirotaka . Ihara . . 2005 . 77 . 20 . 6671–6681 . 10.1021/ac050851v . 16223255 .