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Absence of correlation of hydrogen bond donor ability with acid strength and catalytic activity of acid catalysts (1998)

Fărcaşiu, Dan ; Hâncu, Dan

Springer

Catalysis letters 53 (1998), S. 3-6

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ISSN: 1572-879X

Keywords: acid strength and catalytic activity ; acid strength and H‐bond donor strength ; catalytic activity and acid strength ; catalytic activity and H‐bond donor strength ; H‐bond donor strength and acid strength ; H‐bond donor strength and catalytic activity

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Abstract Two liquids, acetic acid and hexafluoroisopropanol (HFIP), and two solids, silica gel and polymethacrylic acid (PMA), were compared for hydrogen bond donor ability, acid strength, and catalytic activity in typical acid‐catalyzed reactions, inversion of sugar and cleavage of acetone dimethyl ketal. In each pair, the weaker acid (HFIP and silica gel, respectively) was much the stronger hydrogen bond donor, but was totally devoid of catalytic activity, which the poor hydrogen bond donor but stronger acids (acetic and methacrylic acid, respectively) exhibited. A strong hydrogen bond donor (e.g., HFIP) enhances, however, the catalytic activity of the acid catalyst (AcOH). Thus, hydrogen bond donor ability is not a measure of acid strength. A correlation of the two properties is possible only when each group (acids and bases) involved in the comparison consists of very close structural relatives. Such a correlation cannot be extrapolated to any other case.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1019068814279

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Calculation of number and free energy of the conformers of linear alkanes with medium and long chains. Implications for catalysis (1989)

Fǎrcaşiu, Dan ; Walter, Patrick ; Sheils, Kelly

New York, NY [u.a.] : Wiley-Blackwell

Journal of Computational Chemistry 10 (1989), S. 520-528

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ISSN: 0192-8651

Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Computer Science

Notes: A method for calculating the number of rotamers of a linear alkane and of the number of rotamers with a given number of gauche conformations along the chain as a function of the total number of atoms in the chain, using general equations, is presented. A graphical method for generating individual rotamers was applied to the homologs up to decane, which has 1134 rotamers. The steric energies calculated by molecular mechanics (MM2 force field) were used as measures of the heat of formation for the coiled conformations relative to the anti conformer for each molecule, whereas the statistical entropy differences were calculated for classes of coiled rotamers grouped by the number of gauche bonds and steric energy. The free energy values calculated from these components show that already at 400 K hexane exists preferentially in conformations containing gauche bonds. For larger chains the free energy advantage for the coiled chains increases very steeply. The implications for the question of reactions of linear alkanes occurring on the surface or inside the channels of small- and medium-pore zeolites are briefly examined.

Additional Material: 2 Ill.