15 research outputs found
The Energetics of Halogenated Ethylenes (Ethynes) and 1,3-Butadienes (Butadiynes): A Computational and Conceptual Study of Substituent Effects and âDimerizationâ
The energetics of ethylenes and 1,3-butadienes may be interrelated by the reaction:
RHC=CH2 + H2C=CHR\u27 â RHC=CHâCH=CHR\u27 + H2.
Shown earlier to be nearly enthalpically thermoneutral for a variety of hydrocarbon cases, we are now interested in the related energetics of halogenated alkenes and alkynes. Using quantum chemical calculations, we have studied this as recast as the isodesmic reactions:
2(H2C=CHX) + H2C=CHâCH=CH2 â p,q-di-X-1,3-butadiene + 2H2C=CH2
2(HCâĄCX) + HCâĄCâCâĄCH â di-X-butadiyne + 2HCâĄCH.
Here p,q- = 1,3-; 1,4- and 2,3- with X = F, Cl, Br, and I. The halogen and location-dependent deviations from near enthalpic thermoneutrality are discussed
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Dimeric nanocapsule induces conformational change
An induced cisâtransâtrans (rctt) chair to cone structural rearrangement is forced by the addition of a pentacoordinate zinc(II) complex, overcoming thermodynamic and kinetic factors to produce the first phenyl-substituted zinc dimeric nanocapsule
LokĂĄlnĂ struktura kationtovĂœch pozic v dehydratovanĂœch zeolitech odvozenĂĄ z 27Al MAS NMR a DFT vĂœpoÄĆŻ. Studie na Li-, Na-, K-chabazitu
High-resolution Al-27 magic-angle spinning (MAS) NMR spectroscopy of dehydrated M-forms (M = Li, Na, and K) of chabazite in tandem with density functional theory calculations are employed to study the quadrupolar interaction of Al-27 nuclei in dehydrated zeolites and to understand the corresponding high-resolution Al-27 MAS NMR spectra. We show that the broadening of the Al-27 NMR signal in dehydrated zeolites occurs predominantly because of the deformation of the local structure of AlO4- tetrahedra caused by the binding of M+ to the zeolite framework. This deformation increases with the decreasing diameter of the cations from K+ to Li+. The influence of water in hydrated zeolites is limited only to prevent a strong coordination of the M+ cation to O atoms of the AlO4- tetrahedron, but there is no "averaging" effect concerning the local electrostatic field due to molecular motion of water molecules. Our results show that the Al-27 NMR parameters in dehydrated zeolites can be calculated accurately enough to allow the description of the local structure of AlO4- tetrahedra in dehydrated zeolites and to infer the local structure of the sites accommodating the extraframework M+ cations.27Al MAS NMR spektroskopie vysokĂ©ho rozliĆĄenĂ dehydratovanĂœch kationtovĂœch (Li+, Na+, K+) forem chabazitu doprovĂĄzenĂĄ DFT vĂœpoÄty je pouĆŸita ke studiu kvadrupolĂĄrnĂ interakce jader 27Al a k porozumÄnĂ odpovĂdajĂcĂch vysoce rozliĆĄenĂœch 27Al MAS NMR spekter. PĆedvĂĄdĂme zde, ĆŸe pĆĂÄinou rozĆĄĂĆenĂ 27Al MAS NMR spekter v dehydratovanĂœch zeolitech je zejmĂ©na deformace lokĂĄlnĂ struktury ÄtyĆstÄnu AlO4- zpĆŻsobenĂĄ navĂĄzĂĄnĂm kationtu na strukturu zeolitu. Tato deformace se zvÄtĆĄuje se zmenĆĄujĂcĂm se polomÄrem kationtu. Molekuly vody v hydratovanĂœch zeolitech zabraĆujĂ navĂĄzĂĄnĂ kationtu a deformaci ÄtyĆstÄnu AlO4-. NaĆĄe vĂœsledky ukazujĂ, ĆŸe 27Al MAS NMR parametry dehydratovanĂœch zeolitĆŻ mohou bĂœt vypoÄteny s dostateÄnou pĆesnostĂ umoĆŸnujĂcĂ popis lokĂĄlnĂ struktury ÄtyĆstÄnu AlO4- a odvozenĂ lokĂĄlnĂ struktury pozic mimo-mĆĂĆŸkovĂœch kationtĆŻ
The Energetics of Halogenated Ethylenes (Ethynes) and 1,3-Butadienes (Butadiynes): A Computational and Conceptual Study of Substituent Effects and âDimerizationâ
The energetics of ethylenes and 1,3-butadienes may be interrelated by the reaction:
RHC=CH2 + H2C=CHR\u27 â RHC=CHâCH=CHR\u27 + H2.
Shown earlier to be nearly enthalpically thermoneutral for a variety of hydrocarbon cases, we are now interested in the related energetics of halogenated alkenes and alkynes. Using quantum chemical calculations, we have studied this as recast as the isodesmic reactions:
2(H2C=CHX) + H2C=CHâCH=CH2 â p,q-di-X-1,3-butadiene + 2H2C=CH2
2(HCâĄCX) + HCâĄCâCâĄCH â di-X-butadiyne + 2HCâĄCH.
Here p,q- = 1,3-; 1,4- and 2,3- with X = F, Cl, Br, and I. The halogen and location-dependent deviations from near enthalpic thermoneutrality are discussed