Experimental and DFT investigation of structure and IR spectra of H-bonded associates of p-(3-carboxy-1-adamantyl)thiacalix[4]arene

The IR spectra of p-(3-carboxy-1-adamantyl)thiacalix[4]arene (1-AdCOOHTC4A) have been studied. IR spectra of crystalline 1-AdCOOHTC4A obtained at room temperature or upon heating to 250 °C or its dilute solutions lack bands of free hydroxyl groups. The frequency of hydroxyl groups at 3377 cm^-1 indicates the formation of an intramolecular H-bond along the lower rim of the 1-AdCOOHTC4A molecule. On the top edge of thiacalixarene, the carboxyl groups form dimeric or cyclic tetrameric complexes via intermolecular H-bonds. The conformation of the cone persists, but there is a mutual influence of H-bonds along the upper and lower rims of the thiacalix[4]arene molecule. The structure with dimer H-bonds between carboxyl groups is 31.9 KJ/mol less preferable than the conformation with tetramer cyclic H-bonds for 1-AdCOOHTC4A. Comparison of the absorption band of νOH alcohol hydroxyl groups in the IR spectra of 1-AdCOOHTC4A at 3377 cm^-1, with the corresponding band of 1-AdTC4A at 3372 cm^-1, suggests that the presence of the second system of H-bonds of carboxyl groups in the first molecule does not affect the H-bond of alcohol hydroxyl groups.

Vibrational spectroscopic study of cationic phosphorus dendrimers with aminoethylpiperidine terminal groups

Two generations of phosphoric dendrimers with piperidine functional groups were synthesized for use in biology and medicine. Neutral samples are soluble in organic solvents but after protonation these dendrimers become water soluble and can be used for biological experiments. The FTIR and FT Raman spectra of two generations of dendrimers G_i constructed from the cyclotriphosphazene core, repeating units OC₆H₄CHNN(CH₃)P(S)< and aminoethylpiperidine end groups NH(CH₂)₂C₅NH₁₁ were recorded. The study of the IR spectra shows that the NH groups form hydrogen bonds. The calculation of the molecular structure and vibrational spectra of the first generation dendrimer was performed by the method of DFT. This molecule has flat, repeating units and a plane of symmetry passing through the core. The calculation of the distribution of potential energy made it possible to classify the bands in the experimental spectra of dendrimers. Amine groups are manifested in the form of a band of NH stretching vibrations at 3389 cm^-1 in the IR spectrum of G₁. NH⁺ stretching bands located at 2646 and 2540 cm^-1 in the IR spectrum of G₂. The stretching vibrations of NH⁺ groups are noticeably shifted to low frequencies due to the formation of a hydrogen bond with the chlorine atom. The line at 1575 cm^-1 in the Raman spectrum of G₁ is characteristic for repeating units.

Cyclic cooperative intramolecular hydrogen bond in p-tert-butylcalix[6]arene according to FTIR spectroscopy and DFT studies

This article describes a comparative research of IR spectra and H-bonds in the p-tert-butylcalix[6]arene (TB6) and calix[6]arene (C6). IR spectra were computed for compressed cone conformation by DFT method. The assignment of the bands in the IR spectra of the TB6 and C6 was made. The effect of the bulky tert-butyl substituents on the structure and H-bonding in TB6 was established. Our research has shown that in TB6 and C6 the cyclic H-bond is realized, which ensures the existence of a compressed cone conformation. Introduction of tert-butyl substituents in TB6 leads to hardening of H-bonds. Examination of IR spectra showed that when heated TB6 remains in a compressed cone conformation. In a molecule of TB6 and C6 oxygen atoms are in a "boat" conformation.

DFT study of Raman spectra of hexakis(4-N'(-di(4-oxyphenethylamino)-(thio)phosphonyl)-N'-methyl-diazobenzene)cyclotriphosphazene

The FT-Raman spectrum of the hexakis(4-N'(-di(4-oxyphenethylamino)-(thio)phosphonyl)-N'-methyl-diazobenzene)cyclotriphosphazene which is the first generation dendrimer G1 built from the cyclotriphosphazene core, six arms -O-C6H4-CH=N-N(CH3)-P(S)< and twelve 4-oxyphenethylamino terminal groups -O-C6H4-(CH2)2-NH2 G1 has been recorded. The structural optimization and normal mode analysis were performed for model compound C, consisting of cyclotriphosphazene core, one arm -O-C6H4-CH=N-N(CH3)-P(S)< and two 4-oxyphenethylamino terminal groups -O-C6H4-(CH2)2-NH2 on the basis of the density functional theory (DFT) at the PBE/TZ2P level. The calculated geometrical parameters and harmonic vibrational frequencies are predicted in good agreement with the experimental data. It was found that G1 has a concave lens structure with planar -O-C6H4-CH=N-N(CH3)-P(S)< fragments and slightly non-planar cyclotriphosphazene core. The 4-oxyphenethylamino groups attached to different arms show significant deviations from a symmetrical arrangement relative to the local planes of repeating units. The experimental Raman spectra of G1 dendron was interpreted by means of potential energy distribution. Relying on DFT calculations, as well as on experimental information, a spectral interpretation was proposed.

DFT study of Raman spectra of phosphorus-containing dendrons built from cyclotriphosphazene core with terminal carbamate and ester groups

The FT Raman spectra of the zero (Gv0) and first generations (Gv1) of phosphorus-containing dendrons with terminal carbamate groups and one ester function and [2-(4-hydroxyphenyl)ethyl]-carbamic acid tert-butyl ester (C) have been recorded and analyzed. The lines of free ν(C=O) bonds are not observed in the experimental Raman spectrum of C and thus association of carbamate groups by hydrogen bonds occur. The frequencies of ν(C=O) lines in the experimental Raman spectrum reveal the presence of the different types of H-bonds in the amorphous state of Gv0. Density functional theory (DFT) calculations of C gave geometrical parameters for the t-g-, g-g-, tg-, gg-conformers. The most stable is the gg-conformer. The structural optimization and normal mode analysis were performed for dendrons on the basis of the DFT. The calculated geometrical parameters, harmonic vibrational frequencies and Raman intensities are predicted in a good agreement with the experimental data. The experimental Raman spectra of dendrons were interpreted by means of potential energy distribution. Relying on DFT calculations the lines of a core, repeating units and terminal groups of dendrons were assigned. The polarizabilities and lipophilicity of dendrons were estimated.