| Ab initio prediction of the gas- and solution-phase acidities of strong Brønsted acids: the calculation of pKa values less than -10. | |
| | |
MedLine Citation:
|
PMID: 17064194 Owner: NLM Status: PubMed-not-MEDLINE |
Abstract/OtherAbstract:
|
The intrinsic gas-phase acidities of a series of 21 Brønsted acids have been predicted with G3(MP2) theory. The G3(MP2) results agree with high level CCSD(T)/CBS acidities for H(2)SO(4), FSO(3)H, CH(3)SO(3)H, and CF(3)SO(3)H to within 1 kcal/mol. The G3(MP2) results are in excellent agreement with experimental gas-phase acidities in the range 342-302 kcal/mol to within <1 kcal/mol for 14 out of 15 acids. Five of the six acids in the range of 302-289 kcal/mol had an average deviation of 5.5 kcal/mol and the strongest acid, (CF(3)SO(2))(3)CH, deviated by 15.0 kcal/mol. These high-level calculations strongly suggest that the experimental acidities in this very acidic part of the scale need to be remeasured. The CCSD(T)/CBS (mixed exponential Gaussian) additive approach for CH(3)CO(2)H, HNO(3), H(2)SO(4), CH(3)SO(3)H, FSO(3)H, and CF(3)SO(3)H gives excellent agreement (+/-1 kcal/mol) with experiment for the DeltaH(f)(0)'s of non-sulfur containing species, and supports the low end of the experimental values for H(2)SO(4) and FSO(3)H. Use of a larger basis set (aug-cc-pV5Z) in the CBS extrapolation improves the agreement with experiment for both H(2)SO(4) and FSO(3)H. The G3(MP2) heats of formation for RSO(3)H molecules tend to be underestimated as compared to the CCSD(T)/CBS approach by 2.5-7.0 kcal/mol. COSMO solvation calculations were used to predict solution free energies and pK(a) values with pK(a)'s up to -17.4. Including the solvation of the proton gives good agreement with experimental pK(a) values in the very acidic regime, whereas it is less reliable for weaker acids. The use of CH(3)CO(2)H and HNO(3) as reference acids in the less acidic and more acidic regions of the scale, respectively, provided improved results to within +/-2 pK(a) units in nearly all cases (+/-3 kcal/mol accuracy). |
| | |
Authors:
|
Keith E Gutowski; David A Dixon |
Related Documents
:
|
17091434 - Anti-hiv-1 constituents from leaves and twigs of cratoxylum arborescens. 17518044 - Diterpenes from helianthus annuus and their cytotoxicity in vitro. 16725164 - Bioconversion of stemodia maritima diterpenes and derivatives by cunninghamella echinul... 12735684 - A new acylglycosyl sterol from quisqualis fructus. 7151794 - Complete assignment of the 1h nmr spectrum of the aromatic residues of lysozyme. 825224 - The circular dichroic spectra of several sialic acid-containing polysaccharides isolate... |
Publication Detail:
|
Type: Journal Article |
Journal Detail:
|
Title: The journal of physical chemistry. A Volume: 110 ISSN: 1089-5639 ISO Abbreviation: J Phys Chem A Publication Date: 2006 Nov |
Date Detail:
|
Created Date: 2006-10-26 Completed Date: 2007-01-25 Revised Date: 2007-03-27 |
Medline Journal Info:
|
Nlm Unique ID: 9890903 Medline TA: J Phys Chem A Country: United States |
Other Details:
|
Languages: eng Pagination: 12044-54 Citation Subset: - |
Affiliation:
|
Department of Chemistry, Shelby Hall, Box 870336, The University of Alabama, Tuscaloosa, Alabama 35487, USA. |
Export Citation:
|
APA/MLA Format Download EndNote Download BibTex |
| MeSH Terms | |
Descriptor/Qualifier:
|
|
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
Previous Document: Combined multireference configuration interaction/ molecular dynamics approach for calculating solva...
Next Document: Gas phase ion thermochemistry of tetraaza complexes such as cyclamM2+ with H2O, CH3OH, NH3, and othe...