Document Detail

Regioselectivity of pyridine deprotonation in the gas phase.
MedLine Citation:
PMID:  17266374     Owner:  NLM     Status:  MEDLINE    
The regioselective deprotonation of pyridine in the gas phase has been investigated by using chemical reactivity studies. The mixture of regioisomers, trapped as carboxylates, formed in an equilibrium mixture is determined to result from 70-80% deprotonation in the 4-position, and 20-30% deprotonation at the 3-position. The ion formed by deprotonation in the 2-position is not measurably deprotonated at equilibrium because the ion is destabilized by lone-pair repulsion. From the composition of the mixture, the gas-phase acidities (DeltaH degrees acid) at the 4-, 3-, and 2-positions are determined to be 389.9 +/- 2.0, 391.2-391.5, and >391.5 kcal/mol, respectively. The relative acidities of the 4- and 3-positions are explained by using Hammett-Taft parameters, derived by using the measured gas-phase acidities of pyridine carboxylic acids. The values of sigmaF and sigmaR are -0.18 and 0.74, respectively, showing the infused nitrogen in pyridine to have a strong pi electron-withdrawing effect, but with little sigma-inductive effect.
Bonnie S Schafman; Paul G Wenthold
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.     Date:  2007-02-01
Journal Detail:
Title:  The Journal of organic chemistry     Volume:  72     ISSN:  0022-3263     ISO Abbreviation:  J. Org. Chem.     Publication Date:  2007 Mar 
Date Detail:
Created Date:  2007-02-23     Completed Date:  2007-04-24     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  2985193R     Medline TA:  J Org Chem     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1645-51     Citation Subset:  IM    
The Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA.
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MeSH Terms
Carboxylic Acids / chemistry
Hydrocarbons, Aromatic / chemistry
Nitro Compounds / chemistry
Nitrogen / chemistry
Pyridines / chemistry*
Reg. No./Substance:
0/Carboxylic Acids; 0/Hydrocarbons, Aromatic; 0/Nitro Compounds; 0/Protons; 0/Pyridines; 7727-37-9/Nitrogen

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