Experimental and Theoretical Study of the Vibrational Spectra of Free 12-Crown-4

Abstract

The Raman and IR spectra of free 12-crown-4 (12c4) were measured in the solid, liquid, and solution phases. In the three phases, IR active modes were Raman inactive and IR inactive modes were Raman active. According to the exclusion rule, this is consistent with a conformation with a center of inversion. This indicates that 12c4 in the above-mentioned three phases exists in the C(i) conformation. Harmonic force fields were calculated for five of the lowest energy conformations of 12c4 of C(i), S(4), C(4), C(2), and C(s) symmetries at the corresponding optimized geometries at the B3LYP/6-31+G level. The five force fields were scaled using a six-scale-factor scaling scheme. The scale factors were varied to minimize the difference between the calculated and experimental fundamental frequencies, except that corresponding to the C-H stretching mode that was held fixed. The root-mean-square (rms) deviation of the experimental to the calculated vibrational frequencies was 6.2, 12.0, 10.8, 13.2, and 13.5 cm(-1), for C(i)(), S(4), C(4), C(2), and C(s) conformations, respectively. This supports the above conclusion that 12c4 in the solid, liquid, and considered solution phases exists in the C(i) conformation.

Experimental and Theoretical Study of the Vibrational Spectra of 12-Crown-4−Alkali Metal Cation Complexes

“…12c4-alkali metal cation complexes are large ring molecules with 81 normal modes of vibration. While free 12c4 has no redundant internal coordinates, 25 due to symmetry and the additional alkali metal cation, 12c4-alkali metal cation complexes have 90 redundant internal coordinates that were generated by the SCALE2 program. This set of 90 internal coordinates was reduced to 81 nonredundant internal coordinates.…”

“…25 They are mentioned here for completeness. The SCALE2 program has the advantage of minimizing human interference and consequent error.…”

Experimental and theoretical investigations on the keto–enol tautomerism of 4-substituted 3-[1-methylpyrrol-2-yl)methyl]-4,5-dihydro-1H-1,2,4-triazol-5-one derivatives

“…The final scaling was performed with the separate scaling factors for each band. Thus, restricting them to the analyzed functional groups, the proposed scaling factors may lead to an enhancement of the calculated IR frequencies for the similar compounds [65]. As a result of this part of the study it may be concluded that the keto form is the one existing in the solid state.…”

“…The same procedure applied to the spectra recorded in chloroform resulted in the factors 0.8510 and 0.9177 for HF and DFT methods, respectively. To improve further the calculated frequencies, the scaling factors were calculated for each band separately which is a common practice [64,65], with the scaling factors reported up to now the range from about 0.78 to slightly above 1. The summary on the applied scaling factors is given in Table 3.…”

Cs5([12]crown‐4)2(O3)5: A Supramolecular Compound Containing the Confined Ozonide Partial Structure ${{{\hfill 1\atop \hfill \infty }}}${Cs8(O3)10}2−

“…We ascribe these features to the structural confinement of the 5 demonstrates that the interaction between the Cs + ions and the [12]crown-4 molecules is weak: the five characteristic stretching modes of free [12]crown-4 in the fingerprint region, which have been shown to be sensitive to M + ÀO interactions, are not shifted. [23,24] The 19-valence-electron anion O 3 À exhibits the rarely encountered p-electron magnetism, which arises from the one unpaired electron. Ionic ozonides usually display Curie-Weiss paramagnetism, with a tendency towards antiferromagnetic ordering, depending on the intermolecular O···O distance and the type of interaction between the ozonide ions (terminalterminal, terminal-central, or central-central).…”