Hue Anh Nguyen - Academia.edu (original) (raw)

Papers by Hue Anh Nguyen

Research paper thumbnail of Theoretical Study of the Interaction between Methyl Fluoride, Methyl Chloride, and Methyl Bromide with Hydrogen Peroxide

The Journal of Physical Chemistry A, 2004

MP2/6-31+G(d,p) calculations are used to analyze the interaction between CH 3 X (X) F, Cl, or Br)... more MP2/6-31+G(d,p) calculations are used to analyze the interaction between CH 3 X (X) F, Cl, or Br) and hydrogen peroxide (HP). Two stable structures, A and B, are found on each potential energy surface. The A complexes are characterized by a six-membered structure and the B complexes, having a lower stability, by a five-membered structure. In both complexes, the molecules are held together by both OH‚ ‚ ‚X and CH1‚ ‚ ‚O hydrogen bonds. The binding energies range between 2.0 and 3.2 kcal mol-1 for the A complexes and between 1.5 and 1.7 kcal mol-1 for the B complexes. The frequency shifts are calculated for the CH1D2D3X isotopomers. Both A and B complexes exhibit simultaneously an elongation of the OH bond and a red shift and an infrared intensity increase of the corresponding OH stretching vibration along with a contraction of the CH1 bond, a blue shift, and an infrared intensity decrease of the CH1 stretching vibration. The interaction of CH 3 F and CH 3 Cl with HP also induces a contraction of the external CH2 and CH3 bonds and a blue shift of the corresponding stretching vibrations. The results of an NBO analysis are discussed in terms of the hyperconjugation and rehybridization model. While there is a charge transfer from CH 3 X to HP in the A complexes, the charge transfer is negligible in the B complexes. Complex formation results in an increase of the occupation of the σ*(OH) and σ*(CH1) antibonding orbitals and an increase of the s-character of the corresponding O or C atoms. In contrast, there is a decrease in the occupation of the σ*(CH2) and σ*(CH3) orbitals. The n(X) f σ*(OH) hyperconjugative energies are equal to ∼10 kcal mol-1 , and the n(O) f σ*(CH) hyperconjugative energies range between 1.4 and 2.5 kcal mol-1 for the A complexes. Our results show that the OH bond lengths are mainly determined by the occupation of the σ*(OH) orbitals. The CH distances depend on both the occupation of the σ*(CH) orbitals and the hybridization of the corresponding C atom.

Research paper thumbnail of Theoretical Study of the Interaction between Methyl Fluoride, Methyl Chloride, and Methyl Bromide with Hydrogen Peroxide

The Journal of Physical Chemistry A, 2004

MP2/6-31+G(d,p) calculations are used to analyze the interaction between CH 3 X (X) F, Cl, or Br)... more MP2/6-31+G(d,p) calculations are used to analyze the interaction between CH 3 X (X) F, Cl, or Br) and hydrogen peroxide (HP). Two stable structures, A and B, are found on each potential energy surface. The A complexes are characterized by a six-membered structure and the B complexes, having a lower stability, by a five-membered structure. In both complexes, the molecules are held together by both OH‚ ‚ ‚X and CH1‚ ‚ ‚O hydrogen bonds. The binding energies range between 2.0 and 3.2 kcal mol-1 for the A complexes and between 1.5 and 1.7 kcal mol-1 for the B complexes. The frequency shifts are calculated for the CH1D2D3X isotopomers. Both A and B complexes exhibit simultaneously an elongation of the OH bond and a red shift and an infrared intensity increase of the corresponding OH stretching vibration along with a contraction of the CH1 bond, a blue shift, and an infrared intensity decrease of the CH1 stretching vibration. The interaction of CH 3 F and CH 3 Cl with HP also induces a contraction of the external CH2 and CH3 bonds and a blue shift of the corresponding stretching vibrations. The results of an NBO analysis are discussed in terms of the hyperconjugation and rehybridization model. While there is a charge transfer from CH 3 X to HP in the A complexes, the charge transfer is negligible in the B complexes. Complex formation results in an increase of the occupation of the σ*(OH) and σ*(CH1) antibonding orbitals and an increase of the s-character of the corresponding O or C atoms. In contrast, there is a decrease in the occupation of the σ*(CH2) and σ*(CH3) orbitals. The n(X) f σ*(OH) hyperconjugative energies are equal to ∼10 kcal mol-1 , and the n(O) f σ*(CH) hyperconjugative energies range between 1.4 and 2.5 kcal mol-1 for the A complexes. Our results show that the OH bond lengths are mainly determined by the occupation of the σ*(OH) orbitals. The CH distances depend on both the occupation of the σ*(CH) orbitals and the hybridization of the corresponding C atom.