Bonds Of Isomers Research Articles

Nanoscale surface study and reactions mechanism of 2-butanol over the γ-alumina (1 0 0) surface and nanochannel: A DFT study

The mechanism of adsorption, dissociation, hydrogen-shift, dehydration and dehydrogenation of adsorbed ( R)- and ( S)-2-butanol over the dehydroxylated (1 0 0) surface and nanochannel of γ-alumina defect spinel structure was computed by density functional theory (DFT). To test the asymmetric property of this surface by conformational analysis of adsorbed ( R)- and ( S)-2-butanol was investigated. Computed conformational analysis indicates that the ( S)-isomer bond with the surface is stronger than the ( R)-isomer. Steric interactions between adsorbed alcohol and catalyst surface appear to be more important than intramolecular steric constraints present within the alcohol conformations. Mulliken atomic charges predict that selected basic sites (O a–h) play a major role in elimination reactions. E2 elimination with synclinal transition state was comparable with E2 antiperiplanar transition state. The activation energy for elimination of a β-hydrogen from the 2-butanol conformers increases with increasing the distance between β-hydrogen and basic sites. The formation of alkenes (thermodynamic products) is favored over the formation of ketone (kinetic product).

Density functional investigation of reaction of borohydride cation BH2+ with propylene.

The reactions of BH2+ with propylene (CH2=CHCH3) to form both the adducts BC3H8+ and the H2-elimination products BC3H6+ + H2 have been investigated at the density functional B3LYP/6-311G(d,p) level of theory. It is shown that the electrophilic attacks of BH2+ towards two olefinic carbons of H2C=CHCH3 and two subsequent 1,3-H-shifts may form four low-lying BC3H8+ isomers (with the relative energies in parentheses in kcal/mol): 1 BH2+.CH2CHCH3 (0.0), 1' BH2+.CH3CHCH2 (6.3), 3 BHCH2CH2CH3+ (4.3), and 4 BHCH(CH3)2+ (5.0), respectively. On the other hand, further H2-eliminations may also occur easily between B-C bonds of isomers 1 and 1' and between C-C bonds of isomers 3 and 4 to form two dissociation products (P1) HBCHCHCH3+ + H2 and (P2) HBC(CH3)CH2+ + H2, with H2-elimination from isomer 1 to be energetically most favorable. According to our calculated mechanism, the collisional stabilization processes of low-lying isomers 1, 1', 3, and 4 may compete extensively with their H2-eliminations processes for the title reaction, leading mainly to some linear carborane cations. This study may be helpful for understanding the stereochemical aspects of borohydride cations towards alkylenes.