Conformers

In this work we present the thermodynamic and energy results of the lower energy conformation structures of nitrofulerene with the  adsorption of one and two NO2 groups. Benefited by the high symmetry of the fullerene, the inclusion of the first group was facilitated by the adsorption characteristic on the faces of the pentagon. For C60[NO2]1 has its lowest energy conformation at 785,804 kcal / mol, calculated in the classical dynamics, and -2470,415 Hartree, calculated in quantum dynamics. Already for the second group, it was necessary to carry out a search in which carbon the adsorption happens with the lowest energy. Found at this position, C60[NO2]2 has its lower energy conformation at 784,707 kcal / mol and -2674,140 Hartree in the classical and quantum dynamics, respectively. In thermodynamic analysis, the adsorption causes a linear growth in the enthalpy, with greater efficiency at 1000 Kelvin, for entropy at 250 Kelvin, the highest percentage increase, in relation to fullerene, in the heating capacity happens at 75 kelvin and at 50 Kelvin mark the best result for the Gibbs free energy.

Structural and energetic consequences of replacing one or more carbon atoms in small cyclic hydrocarbons with electronegative atoms have been observed due to stereoelectronic anomeric and gauche effects. We have reported the influence of gauche effect on the conformational behavior of a 1,4-diazacyclohexane system using the DFT B3LYP/6-311 + G** level of theory. Factors which are found to control the conformational preferences of a 1,4-diazacyclohexane system include steric, dipolar repulsions and hyperconjugative interactions. The stability order of the 1,4-diazacyclohexane conformers was predicted to be similar in the gas phase and solvent continuum model (aqueous phase). The interactions of explicit water molecules with 1,4-diazacyclohexane conformers however predicted a different order of stability compared to the gas phase and continuum phase results. Ab initio molecular dynamics (AIMD) study showed the minor perturbation in the orientation of explicit water molecules compared to the DFT results and no dramatic changes was observed during the simulation with 1,4-diazacyclohexane conformers.

Abstract: The contemporary organometallic chemistry stems from the discovery of ferrocene Fe(C5H5)2, i.e., di-cyclopentadienyle iron (FeCp2 or Fc) half a century ago [1,2]. Since its discovery, the heated debate whether the eclipsed or the staggered is the most stable structure of Fc continues. The fact that electronic structures and many properties of the Fc conformers are strikingly similar has been a key hurdle to differentiate or separate the configurations from one another [3]. We recently discovered theoretically using DFT calculations that the 400-500 cm-1 region of the infrared (IR) spectra of Fc [4] exhibits the fingerprint conformers. Such the discovery was later confirmed by IR experimental measurements in a number of solutions, in polar and non-polar solvents [5]. Understanding of the structure and dynamics of the sandwich complex is important as Fc derivatives may inherit particular properties which only exist in one conformer such as catalysis. It is further discovered...

The photodissociation dynamics of iodocyclohexane has been studied using velocity map imaging following excitation at many wavelengths within its A-band (230≤ λ≤ 305 nm). This molecule exists in two conformations (axial and equatorial), and one aim of the present experiment was to explore the extent to which conformer-specific fragmentation dynamics could be distinguished. Ground (I) and spin-orbit excited (I*) state iodine atom products were monitored by 2+ 1 resonance enhanced multiphoton ionization, and total kinetic energy ...

The conformational flexibility of the Z and E isomers of cefotaxime
(CFX) and thiazoximic acid, their ground-state isomerization path and transition state, were all analyzed in depth. The modeling was carried at the semiempirical and DFT-BLYP level with geometry optimization for gas phase conditions. That approach was used after a thorough analysis using classical molecular dynamics to initially define large families of conformers. The lowest energy conformers always have an E configuration, in contradiction to the behavior observed in solution, and the Z–E
isomerization mechanism is a rotation. These results reveal the remarkable flexibility of these molecules, allow anticipating the role of water and of their target proteins in the redistribution of the conformers population, and provide the best geometry known for CFX.