In situ X-ray structural studies of a flexible host responding to incremental gas loading

Crystallographic pressure-lapse snapshots of a porous material responding to gas loading were used to investigate the stepwise uptake of carbon dioxide and acetylene molecules into discrete confined spaces. Based on the data, a qualitative statistical mechanical model was devised that reproduces even subtle features in the experimental gas sorption isotherms.     

Free Radical Isomerizations in Acetylene Bromoboration Reaction

The experimentally motivated question of the acetylene bromoboration mechanism was addressed in order to suggest possible radical isomerization pathways for the syn-adduct. Addition–elimination mechanisms starting with a bromine radical attack at the “bromine end” or the “boron end” of the C=C bond were considered. Dispersion-corrected DFT and MP2 methods with the SMD solvation model were employed using three all-electron bases as well as the ECP28MWB ansatz. The rate-determining, elimination step had a higher activation energy (12 kcal mol⁻¹) in case of the “bromine end” attack due to intermediate stabilization at both the MP2 and DFT levels. In case of the “boron end” attack, two modes of C–C bond rotation were followed and striking differences in MP2 vs. DFT potential energy surfaces were observed. Employing MP2, addition was followed by either a 180° rotation through an eclipsed conformation of vicinal bromine atoms or by an opposite rotation avoiding that conformation, with 5 kcal mol⁻¹ of elimination activation energy. Within B3LYP, the addition and rotation proceeded simultaneously, with a 9 (7) kcal mol⁻¹ barrier for rotation involving (avoiding) eclipsed conformation of vicinal bromines. For weakly bound complexes, ZPE corrections with MP2 revealed significant artifacts when diffuse bases were included, which must be considered in the Gibbs free energy profile interpretation.     

First Example of Construction of a Pyrrole Ring Bonded to a Steroid System by the Trofimov Reaction

The oxime of ⁵-pregnen-3-ol-20-one reacts with acetylene in the KOH-DMSO system to form a mixture of products containing 3-vinyloxy-17-(1-vinyl-2-pyrrolyl)-⁵-androstene as the major product (63% yield) and also the O-vinyloxime of 3-vinyloxy-⁵-pregnen-20-one (10%), 3-vinyloxy-17- and 3-vinyloxy-17-⁵-pregnen-20-one (25%, 1:4 ratio).     

粒径对煤在H2/Ar等离子体中热解的影响

对粒径在H2／Ar等离子体煤热解制乙炔中的影响进行了研究，得到了煤的粒径与煤的裂解程度（转化率）、乙炔收率、乙炔在产品气体中摩尔分数和反应器壁结焦的关系，并且在考虑各种因素的制约下，对如何选择最佳粒径和粒径分布的问题进行了讨论。根据煤等离子体热解制乙炔反应器壁结焦的机理和煤粒径是影响反应器内结焦的重要因素，提出了进料粒径双峰分布缓解煤等离子体热解制乙炔装置结焦的新方法，实验证明该方法可行。     

Kinetics of the catalytic hydrochlorination of acetylene on the surface of mechanically preactivated K2PtCl4

The hydrochlorination of acetylene by gaseous HCl is catalyzed at room temperature on the surface of dry K₂PtCl₄ subjected to mechanical preactivation in an acetylene atmosphere. The acetylene hydrochlorination product is formed by trans addition. The kinetic isotope effect (KIE) upon replacing HCl by DCl is 5 ± 1, which is much greater than the KIE found in the catalytic hydrochlorination of acetylene on the surface of mechanically preactivated K₂PtCl₆ (1.9). This discrepancy suggests different reaction mechanisms in these two systems. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 3, pp. 173–177, May–June, 2006.     

Quantum-chemical models of KOH(KOBut)/DMSO superbasic systems and mechanisms of base-promoted acetylene reactions

The mechanisms of fundamental base-promoted acetylene reactions, namely, nucleophilic addition to the triple C ≡ C bond (vinylation) and nucleophilic addition of acetylenic carbanion to a carbonyl group (ethynylation), are addressed using three models of different complexity—pentasolvate, monosolvate, and anionic—which describe the catalytic superbasic systems MOH(OBu^t)/DMSO (suspensions of alkali hydroxides or tert-butoxides in dimethyl sulfoxide). The above acetylene reactions and sequential transformations of reagents arranged by the superbasic center are modeled within the framework of the most complete pentasolvate model, in which the superbase is represented by the KOH·5DMSO (KOBu^t·5DMSO) complexes. We have developed approaches to the construction of simplified models (monosolvate and anionic) to describe transformations in complex systems. The mechanisms of cascade assemblies of 6,8-dioxabicyclo[3.2.1]octanes, cyclopentenones, and furan cycles from ketones and acetylenes in the superbasic environment are investigated using a uniform B2PLYP/6-311+G**//B3LYP/6-31+G* approach, and the energy profiles of these different carbo- and heterocycles are analyzed.     

First total synthesis of neurotrophic diacetylene tetrol (−)-petrosiol D

The first total synthesis of the natural product (−)-petrosiol D has been achieved in a linear fashion. Sharpless asymmetric epoxidation, base induced elimination reaction for the formation of chiral propargyl alcohol and Cadiot–Chodkiewicz coupling reaction are the key steps utilized for the synthesis.