Substituent effects on the energetics and aromaticity of aminomethylbenzoic acids

• Type: Article in International Scientific Journal
• Date: 2007

Authors

Carlos F R A C Lima (Author) Other; Ligia R Gomes (Author) Other; Luis M N B F Santos (Author) FCUP

Journal

Title: Journal of Physical Chemistry A

Vol. 111

Pages: 10598-10603

ISSN: 1089-5639

Publisher: American Chemical Society

Indexing

ISI Web of Knowledge - 15 Citations

Scopus - 17 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Other information

Authenticus ID: P-004-6R0

DOI: 10.1021/jp073077j

Abstract (EN): The standard (p(0) = 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 (D(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.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 6