CAREER NETWORK World's one of the largest Research Career Network Benefits Academic & Industry jobs Project funding Visiting faculty positions Visiting scientist positions Invited talks and more... Register FREE Journal of Spectroscopy and Dynamics 2014, 4: 7 Research Article The infrared vibrational modes and relative strength of unusual-π···H and pseudo-π···H weak hydrogen bonds Boaz G. Oliveira Institute of Environmental Sciences and Sustainable Development (ICADS), Federal University of Bahia, 47801-100, Barreiras – BA, Brazil Abstract Through the B3LYP/6-311++G(d,p) calculations, this work reports novel endeavors about a special class of hydrogen bonds (π···H and σ···H) formed by π (C3H4) or σ (C4H4) bonds as proton acceptors whose equivalent donors are those derived from monoprotic acids (HX with X = F and Cl). The hydrogen bond energies and red-shifted frequencies of the proton donors (Δν Str) were evaluated in accordance with charge transfers amounts calculated through the ChelpG and NBO approaches. The variations in the percentage of the π orbital of X were correlated with the results of red-shifts and NBO energies in order to confirm the weakness of the proton donors upon complexation. The QTAIM integrations were applied to characterize the π···H and σ···H hydrogen bonds as well as to demonstrate an efficient procedure to estimate the interaction strength based on the correlation between topological descriptors (electronic density and Laplacian) and infrared stretching modes (red-shifts). Keywords Hydrogen bonds; Infrared spectra; Charge transfer; NBO; QTAIM