Document Detail


The Effect of Hydrogen Bonds on pKa's: The Importance of Networking.
MedLine Citation:
PMID:  22656241     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
The pKa of an acyclic aliphatic heptaol ((HOCH2CH2CH(OH)CH2)3COH) was measured in DMSO and its gas-phase acidity is reported as well. This tertiary alcohol was found to be 1021 times more acidic than tert-butanol in DMSO and an order of magnitude more acidic than acetic acid (i.e., pKa = 11.4 vs 12.3). This can be attributed to a 21.9 kcal mol-1 stabilization of the charged oxygen center in the conjugate base by three hydrogen bonds, and another 6.3 kcal mol-1 stabilization resulting from an additional three hydrogen bonds between the uncharged primary and secondary hydroxyl groups. Charge delocalization by both the first and second solvation shells maybe used to facilitate enzymatic reactions. Acidity constants of a series of polyols were also computed, and the combination of hydrogen bonding and electron withdrawing substituents was found to afford acids that are predicted to be extremely acidic in DMSO (i.e., pKa < 0). These hydrogen bond enhanced acids represent an attractive class of BrØnsted acid catalysts.
Authors:
Alireza Shokri; Azardokht Abedin; Alireza Fattahi; Steven Robert Kass
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-6-2
Journal Detail:
Title:  Journal of the American Chemical Society     Volume:  -     ISSN:  1520-5126     ISO Abbreviation:  -     Publication Date:  2012 Jun 
Date Detail:
Created Date:  2012-6-4     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  7503056     Medline TA:  J Am Chem Soc     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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