Document Detail


Substituent effects on the energetics and aromaticity of aminomethylbenzoic acids.
MedLine Citation:
PMID:  17914759     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The standard (p0 = 0.1 MPa) molar enthalpies of combustion of six aminomethylbenzoic acids were measured at T = 298.15 K by static bomb calorimetry. With these values, the standard molar enthalpies of formation in the crystalline state were obtained. Combining these results with the standard molar enthalpies of sublimation, the standard molar enthalpies of formation in the gaseous phase were derived. For the 10 possible isomers, the obtained experimental results were compared to and correlated with the relative stability obtained by ab initio calculations at the B3LYP/6-311++G(d,p) level of theory. Seeking a better understanding of the aromatic behavior and energetics of aminomethylbenzoic acids in the gas phase, calculations of NICS values, HOMA indices, and dihedral angles between the aromatic carbon and the amino group, Phi(Ar-NHH), were also performed computationally. The significant differences observed in the energetics, as well as in the NICS values, HOMA indices, and Phi(Ar-NHH) dihedral angles for these 10 isomers suggest a strong dependency on the identity and relative position of the three substituents on the benzene ring. This study points out a marked tendency for a decrease of the ring aromaticity, accompanied by an increase in the respective system stability, as the conjugation between the substituents becomes more extensive.
Authors:
Carlos F R A C Lima; Lígia R Gomes; Luís M N B F Santos
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2007-10-03
Journal Detail:
Title:  The journal of physical chemistry. A     Volume:  111     ISSN:  1089-5639     ISO Abbreviation:  J Phys Chem A     Publication Date:  2007 Oct 
Date Detail:
Created Date:  2007-10-18     Completed Date:  2008-01-10     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9890903     Medline TA:  J Phys Chem A     Country:  United States    
Other Details:
Languages:  eng     Pagination:  10598-603     Citation Subset:  IM    
Affiliation:
Centro de Investigação em Química, Departamento de Química, Faculdade de Ciências, Universidade do Porto, R Campo Alegre 687, 4169-007 Porto, Portugal.
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MeSH Terms
Descriptor/Qualifier:
4-Aminobenzoic Acid / analogs & derivatives*,  chemistry
Algorithms*
Amines / chemistry
Calorimetry
Carbon / chemistry
Gases
Hydrocarbons, Aromatic / chemistry*
Isomerism
Thermodynamics
Chemical
Reg. No./Substance:
0/Amines; 0/Gases; 0/Hydrocarbons, Aromatic; 150-13-0/4-Aminobenzoic Acid; 56-91-7/4-aminomethylbenzoic acid; 7440-44-0/Carbon

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