Comment/Reply pubs.acs.org/jced
Comment on “The Effect of Surface Adsorption and Molecular Geometry on the Determination of Henry’s Law Constants for Fluorotelomer Alcohols” Sierra Rayne* Chemologica Research, PO Box 74, 318 Rose Street, Mortlach, Saskatchewan S0H 3EO, Canada
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n their article, Wu and Chang1 measure the Henry’s Law constants for the 4:2, 6:2, 8:2, and 10:2 fluorotelomer alcohols (FTOH) and interpret their observed trends in measured Henry’s Law constants with perfluoroalkyl chain length within the context of relative molecular geometries for the compounds under consideration. Upon measuring similar Henry’s Law constants (KH) for the 6:2, 8:2, and 10:2 FTOH, the authors state that “we expect these unusual phenomena may also indicate the influence of the molecular structure of FTOHs to their physicochemical properties, since all experimental KH data of FTOHs displayed similar trends. It is reported that, unlike hydrocarbons, the geometry of fluorocarbons changes as the chain length increases to minimize the steric hindrance due to the larger van der Waals radius of fluorine than hydrogen. If the CF2 units are less than eight, the fluorocarbon segments mainly form a planar and flexible zigzag conformation, while with more than eight CF2 units, a slight distortion at each CF2 leads to a helix conformation, which increases strongly with the increasing number of CF2 units. The change of molecular geometry with increasing fluorocarbon chain would impact electron density distribution within molecules and the free energy of thermodynamic process.” This is not a correct assessment regarding the state-of-the-art surrounding the geometry of perfluoroalkane chains. Prior work (see, refs 2 to 4 and references therein) has established that the zigzag conformation of C4 and longer perfluoroalkyl chains is a transition state between left- and right-handed helical global minima. As such, the geometrical explanation invoking a zigzag global minimum conformation for n:2 (n < 8) FTOH by Wu and Chang1 does not appear to be valid.
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sulfonic acids, alkanes, and alcohols. J. Mol. Struc. THEOCHEM 2010, 941, 107−118. (4) Rayne, S.; Forest, K. Theoretical studies on the all-anti zigzag geometries of perfluoro-n-alkyl chains. Nat. Preced. 2010, DOI: 10.1038/npre.2010.5061.1.
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[email protected]. Tel.: + 1 306 690 0573. Fax: + 1 306 690 0573. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Wu, Y.; Chang, V. W. C. The effect of surface adsorption and molecular geometry on the determination of Henry’s Law constants for fluorotelomer alcohols. J. Chem. Eng. Data 2011, 56, 3442−3448. (2) Rayne, S.; Forest, K. Theoretical studies on the pKa values of perfluoroalkyl carboxylic acids. J. Mol. Struc. THEOCHEM 2010, 949, 60−69. (3) Rayne, S.; Forest, K. Comparative semiempirical, ab initio, and density functional theory study on the thermodynamic properties of linear and branched perfluoroalkyl sulfonic acids/sulfonyl fluorides, perfluoroalkyl carboxylic acid/acyl fluorides, and perhydroalkyl © 2013 American Chemical Society
Received: March 2, 2013 Accepted: April 8, 2013 Published: April 17, 2013 1417
dx.doi.org/10.1021/je400210g | J. Chem. Eng. Data 2013, 58, 1417−1417
