Structure and Conformations of Six-Membered Systems A6H12 (A = C, Si): Ab Initio Study of Cyclohexane and Cyclohexasilane

Leong, Max K.; Mastryukov, V. S.; Boggs, James E.

doi:10.1021/j100079a013

Cited by 41 publications

(41 citation statements)

References 2 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…On the contrary, only chair cyclohexane (D 3d symmetry) has been considered for calculation, since twist cyclohexane (the second minimum, D 2 symmetry) has energy ¾6.5 kcal/mol higher than chair. 19,26 Calculated bond lengths of (1) match satisfactorily the experimental data from X-ray diffraction studies. 34,35 In particular, for the peroxide bridge C 3 O 2 O 1 C 12a , bond lengths are calculated 1.415 (C 3 -O 2 ), 1.456 (O 2 -O 1 ) and 1.458 (O 1 -C 12a )Å, in good agreement with X-ray values, Figure 2.…”

Section: Equilibrium Geometriessupporting

confidence: 64%

See 1 more Smart Citation

Raman and infrared characterization of the vibrational properties of the antimalarial drug artemisinin

Moroni

Gellini

Miranda

et al. 2008

J Raman Spectroscopy

View full text Add to dashboard Cite

Artemisinin is one of the most powerful new generation antimalarial drugs. The active center is the peroxide group of the caged trioxane heterocycle, which either blocks the free heme released by the Plasmodium falciparum parasite or acts on key proteins causing the parasite death. Both processes involve the activation of the 1,2,4-trioxanic ring through interaction with the Fe(II)-heme complex. Since considerable effort was made to synthesize antimalarial drugs containing the endoperoxide group, it becomes fundamental to know the structural and dynamical properties of artemisinin. For this reason, Raman and Fourier transform (FT) infrared studies have been undertaken here on the vibrational properties of artemisinin, its derivative artemether and d-valerolactone, the latter being the molecule mimicking the lactonic ring of artemisinin. The vibrational data of the three molecules have been analyzed through the comparison with ab initio calculations based on DFT/B3-LYP/cc-pVDZ procedures. Modes of artemisinin have been correlated with those of component units.

show abstract

Section: Equilibrium Geometriessupporting

confidence: 64%

“…26,34,35 Two sets of values are reported for (6), relative to the halfchair and boat conformations, as the vibrational analysis shows that both conformations contribute to the room temperature spectra of (6). The energy difference in favor of the half-chair is 0.8 kcal/mol, according to our calculation.…”

Section: Equilibrium Geometriesmentioning

confidence: 99%

Raman and infrared characterization of the vibrational properties of the antimalarial drug artemisinin

Moroni

Gellini

Miranda

et al. 2008

J Raman Spectroscopy

View full text Add to dashboard Cite

show abstract

“…[5,6] Finally, for cyclohexasilane, Leong et al carried out MP2/6-31G* calculations and found a barrier for the ring inversion of only~15 kJ mol À1 and a twist conformer with DE = 8 kJmol À1 . [7] These results show that the greatest decrease in ring inversion barriers in this series occurs due to the exchange of only one carbon atom by a silicon atom.…”

mentioning

confidence: 71%

“…For cyclohexane itself, the axial CÀH bond was found to be 2 pm longer than the equatorial by MP2 calculations. [7] Using microwave spectroscopy, the axial bond was determined to be even 9 pm longer. [24] For cyclohexasilane, the axial bond is longer by 5 pm as well.…”

Section: Experimental and Computational Methodsmentioning

confidence: 99%

The Cyclohexasilanes Si₆H₁₁X and Si₆Me₁₁X with X=F, Cl, Br and I: A Quantum Chemical and Raman Spectroscopic Investigation of a Multiple Conformer Problem

2007

View full text Add to dashboard Cite

The conformers of the monohalocyclohexasilanes, Si(6)H(11)X (X=F, Cl, Br or I) and the haloundecamethylcyclohexasilanes, Si(6)Me(11)X (X=F, Cl, Br or I) are investigated by DFT calculations employing the B3LYP density functional and 6-31+G* basis sets for elements up to the third row, and SDD basis sets for heavier elements. Five minima are found for Si(6)H(11)X-the axial and equatorial chair conformers, with the substituent X either in an axial or equatorial position-and another three twisted structures. The equatorial chair conformer is the global minimum for the X=Cl, Br and I, the axial chair for X=F. The barrier for the ring inversion is approximately 13 kJ mol(-1) for all four compounds. Five minima closely related to those of Si(6)H(11)X are found for Si(6)Me(11)X. Again, the equatorial chair is the global minimum for X=Cl, Br and I, and the axial chair for X=F. Additionally, two symmetrical boat conformers are found as local minima on the potential energy surfaces for X=F, Cl and Br, but not for X=I. The barrier for the ring inversion is approximately 14-16 kJ mol(-1) for all compounds. The conformational equilibria for Si(6)Me(11)X in toluene solution are investigated using temperature dependent Raman spectroscopy. The wavenumber range of the stretching vibrations of the heavy atoms X and Si from 270-370 cm(-1) is analyzed. Using the van't Hoff relationship, the enthalpy differences between axial and equatorial chair conformers (H(ax-)H(eq.)) are 1.1 kJ mol(-1) for X=F, and 1.8 to 2.8 kJ mol(-1) for X=Cl, Br and I. Due to rapid interconversion, only a single Raman band originating from the "averaged" twist and boat conformers could be observed. Generally, reasonable agreement between the calculated relative energies and the experimentally determined values is found.

show abstract

“…the pre-exponential factor in the Arrhenius equation is smaller. The activation energy is not important in accounting for the slower kinetics, since energy barriers for geometry changes of cyclohexasilanes are similar to those of n-alkanes [18,19]. Nevertheless, this flexibility of the silicon ring must play an important role in the formation of the excimer.…”

mentioning

confidence: 99%

Intramolecular excimer and exciplex emission of 1,4-dipyrenyl substituted cyclohexasilane

Walree

Kaats-Richters²,

Jenneskens³

et al. 2002

Chemical Physics Letters

View full text Add to dashboard Cite

Intramolecular excimer emission is observed for cis-1,4-di(1-pyrenyl)decamethylcyclohexasilane in nonpolar solvents. Time-resolved fluorescence spectroscopy and kinetic modelling indicate that the driving force of excimer formation is very small, and that the process is governed by the flexibility of the silicon ring. In the polar solvent acetonitrile, photoinduced electron transfer occurs, with the cyclohexasilane ring acting as electron donor and the pyrenyl group as electron acceptor. Ó

show abstract

Structure and Conformations of Six-Membered Systems A6H12 (A = C, Si): Ab Initio Study of Cyclohexane and Cyclohexasilane

Cited by 41 publications

References 2 publications

Raman and infrared characterization of the vibrational properties of the antimalarial drug artemisinin

Raman and infrared characterization of the vibrational properties of the antimalarial drug artemisinin

The Cyclohexasilanes Si₆H₁₁X and Si₆Me₁₁X with X=F, Cl, Br and I: A Quantum Chemical and Raman Spectroscopic Investigation of a Multiple Conformer Problem

Intramolecular excimer and exciplex emission of 1,4-dipyrenyl substituted cyclohexasilane

Contact Info

Product

Resources

About

Structure and Conformations of Six-Membered Systems A6H12 (A = C, Si): Ab Initio Study of Cyclohexane and Cyclohexasilane

Cited by 41 publications

References 2 publications

Raman and infrared characterization of the vibrational properties of the antimalarial drug artemisinin

Raman and infrared characterization of the vibrational properties of the antimalarial drug artemisinin

The Cyclohexasilanes Si6H11X and Si6Me11X with X=F, Cl, Br and I: A Quantum Chemical and Raman Spectroscopic Investigation of a Multiple Conformer Problem

Intramolecular excimer and exciplex emission of 1,4-dipyrenyl substituted cyclohexasilane

Contact Info

Product

Resources

About

The Cyclohexasilanes Si₆H₁₁X and Si₆Me₁₁X with X=F, Cl, Br and I: A Quantum Chemical and Raman Spectroscopic Investigation of a Multiple Conformer Problem