A stochastic search of the potential energy surface for the formic acid dimers results in 21 well-defined minima. A number of structures are reported here for the first time, others have already been experimentally detected or computationally predicted. Four types of different hydrogen bonds (HBs) are at play stabilizing the clusters: primary C=O⋯ H-O and H-O⋯ H-O and secondary C=O⋯ H-C and H-O⋯ H-C HBs corresponding to well-characterized bonding paths are identified. A novel C=O⋯ C stabilizing interaction is also reported. The double proton transfer reaction is calculated to occur in a synchronous fashion, with an energy barrier smaller than the energy needed to break up the dimers.
The metathesis of alkanes is a process in which a given alkane is transformed into higher and lower homologues. Here, we carried out DFT calculations in order to get insights into the most favorable reaction pathway for the metathesis of propane into mainly ethane and butane catalyzed by a silica-supported molybdenum alkylidene bearing an imido ligand at 150 °C. The overall catalytic process is divided into two stages, precursor activation and catalytic cycle, and both of them consist of the same types of reactions, (i) ligand exchange, (ii) proton transfer between two α-carbons, and (iii) ligand rearrangement, which in turn consists of several steps, such as β-H elimination, alkene cross-metathesis, and alkene insertion. Our results suggest that the formal ligand exchange reaction with propane proceeds through a dissociative mechanism with the formation of a high-energy molybdenum alkylidyne species. The calculated energetics at 150 °C indicates that the active species is a molybdenum propylidene species that is formed with an overall Gibbs activation barrier of 39.4 kcal mol −1 . The catalytic cycle to the main products (ethane and butane) has an energy span of 43 kcal mol −1 , whereas the cycle for the production of minor products (methane and pentane) has a much higher energy span, in agreement with experiments. These data suggest that the catalytic cycle is the rate-determining stage in the whole process and thus the precursor activation should be faster. The results obtained here help to rationalize the chemical reactivity of supported molybdenum alkylidene catalysts toward alkanes.
The aim of this study was to estimate the intake of dry matter forage (CMSf) by grazing holstein cows. The research was conducted in northern Antioquia highlands; a silvopastoral system with Tithonia diversifolia and Cenchrsus clandestinum (SSP) and a monoculture C. clandestinum were used. Were estimated the CMSf by different methodologies and kikuyu:wild sunflower consumption relation, also the interchangeability of two methodologies was determined. There were two conducted trials, in the first trail SSP was used without browsing of wild sun ower and monoculture; in the second trial the same system was applied, with the difference that for the SSP animals browsed the shrubby by themselves. Twelve random infant holstein cows were used in the two systems. CMSf was estimated by indicators (I), agronomic (A) and grazing behavior (C) methods, method I was the reference. In trial I more CMSf was observed in the SSP, with an average of 14.7 kg/day (p<0.05); trial II showed no difference in the CMSf, with an average of 13.3 kg/day (p>0.005). The kikuyu:wild sunflower consumption relation was 95:5. The correlation coefficient of concordance between the methods I and C near to 0 shown that they are not interchangeable. The results suggest that the SSP evaluated supplied sufficient forage to ensure optimal CMSf.
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