Electrophilic Reactivity of Tetrabromorhodamine 123 is Bromine Induced: Convergent Interpretation through Complementary Molecular Descriptors

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 116; no. 48; pp. 11938 - 11945
• Main Authors: Ferreira, José A. B, Sánchez-Coronilla, Antonio, Togashi, Denisio M, Ferreira, Humberto, Ascenso, José R, Costa, Sílvia M. B
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 06-12-2012
• Subjects: Benzoates; Bonding; Bromine - chemistry; Cations; Chemical bonds; Electrons; Free energy; Hydrophobic and Hydrophilic Interactions; Methanol - chemistry; Methyl alcohol; Molecular Structure; Perturbation theory; Physical chemistry; Quantum Theory; Rhodamines - chemical synthesis; Rhodamines - chemistry; Water - chemistry
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp307461m

Nucleophilic addition of water and of methanol to 3,6-diamino-2,4,5,7-tetrabromo-9-[2-(methoxycarbonyl) phenyl]-9H-xanthen-9-ylium, 4BrR123, yields respectively 2-(3,6-diamino-2,4,5,7-tetrabromo-9-hydroxy-9H-xanthen-9-yl)xanthyl benzoate, HO4BrR123 and 2-(3,6-diamino-2,4,5,7-tetrabromo-9-methoxy-9H-xanthen-9-yl)xanthyl benzoate, MeO4BrR123. The novel experimental results are addressed theoretically. The linear free energy relationship, LFER, second-order perturbation theory analysis of the natural bond orbital, NBO, and quantum theory of atoms in molecules, QTAIM, lead to the same conclusion: the electron-withdrawing effect of bonded Br atoms in 4BrR123 extremely enhances the molecular electrophilicity, as compared to 3,6-diamino-9-[2-(methoxycarbonyl) phenyl]-9H-xanthen-9-ylium, R123. The reactivity of these diaminoxanthylium cations is discussed in the context of local and global softness in extended conjugated systems.