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Conformational stability and vibrations of aminopropylsilanol molecule

Density functional theory, using the B3-LYP/6-31G(d, p) method have been used to investigate the conformation and vibrational spectra of aminopropylsilanetriol (APST) NH2CH2CH2CH2Si(OH)3. The potential function for CCCSi torsion gives rise to two distinct conformers trans and gauche. The predicted energy of the more stable trans conformer is 337 cm-1 less than the energy of gauche conformer. The calculated barriers to the conformation interchange are: 1094.5, 2845.0 and 437.8 cm-1 for the trans to gauche, gauche to gauche and gauche to trans conformers, respecively. For the trans conformer the potential energy curve for the Si(OH)3 groups torsion in APST has been calculated changing the HOSiC dihedral angle. The barrier for the internal rotation of 3064.6 cm-1 has been obtained. The optimized molecular structure of APST dimer calculated for trans conformer has a Si-O-Si angle of 143.24 , and a Si-OSi bond length of 0.164 nm. A complete vibrational assignment for both conformers as well as for trans-dimer is supported by the normal coordinate analysis, calculated IR intensities as well as Raman activities. On the basis of the results, the vibrational spectra of APST aqueous solution and APST polimer have been analyzed. The average error between the observed and calculated frequencies is 14 cm-1.

trans and gauche aminopropylsilanetriol ; dimer ; DFT

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