The IR and Raman spectra and conformations of the ionic liquid 1-ethyl-3-methyl-1H-imidazolium tetrafluoroborate, [EMIM] [BF 4 ] (6), were analyzed within the framework of scaled quantum mechanics (SQM). It was shown that SQM successfully reproduced the spectra of the ionic liquid. The computations revealed that normal modes of the EMIM ¥ BF À 4 ion pair closely resemble those of the isolated ions EMIM and BF À 4 , except for the antisymmetric BF stretching vibrations of the anion, and the out-of-plane and stretching vibrations of the HÀC(2) moiety of the cation. The most plausible explanation for the pronounced changes of the latter vibrations upon ion-pair formation is the H-bonding between HÀC(2) and BF À 4 . However, these weak H-bonds are of minor importance compared with the Coulomb interactions between the ions that keep them closely associated even in dilute CD 2 Cl 2 solutions. According to the −gas-phase× computations, in these associates, the BF À 4 anion is positioned over the imidazolium ring of the EMIM cation and has short contacts not only with the HÀC(2) of the latter, but also with a proton of the MeÀN(3) group.
The IR and Raman spectra and conformations of calix[4]arene, thiacalix[4]arene and their p-tert-butyl derivatives have been analysed within the framework of scaled quantum mechanics (SQM). It is shown that the introduction of four p-tert-Bu groups into the calixarene molecules influences the relative energies of their conformers and the enthalpy of the cooperative intramolecular H-bonding (DeltaH(intra)) almost negligibly. DeltaH(intra), evaluated from Iogansen's rule, amounts to approximately 26-28 kcal mol(-1) for the calixarenes and approximately 20-21 kcal mol(-1) for the thiacalixarenes, which essentially exceeds the enthalpies of non-cooperative H-bonds formed by related phenols. As a result of this strong bonding, bands of stretching, bending and torsion vibrations of an eight-membered cyclic system (OH...)4 arise, e.g., two delta(OH)4 bands are observed in the IR spectra of the most highly symmetric C4 cone conformations of calix[4]arene and thiacalix[4]arene. The "duplication" of the number of OH infrared bands is a good new indicator of cooperativity of intramolecular H-bonding of the calixarenes.
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