Hydrogen Cyanide Exchange on [Al(HCN) 6 ] 3+ - A DFT Study (original) (raw)
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Phys. Chem. Chem. Phys., 2015
The different HCN elimination pathways from vinyl cyanide (VCN) are studied in this paper using RRKM, Kinetic Monte Carlo (KMC), and quasi-classical trajectory (QCT) calculations. A new HCN elimination pathway proves to be very competitive with the traditional 3-center and 4-center mechanisms, particularly at low excitation energies. However, low excitation energies have never been experimentally explored, and the high and low excitation regions are dynamically different. The KMC simulations carried out using singly deuterated VCN (CH 2 QCD-CN) at 148 kcal mol À1 show the importance of hydrogendeuterium exchange reactions: both DCN and HCN will be produced in any of the 1,1 and 1,2 elimination pathways. The QCT simulation results obtained for the 3-center pathway are in agreement with the available experimental results, with the 4-center results showing much more excitation of the products. In general, our results seem to be consistent with a photodissociation mechanism at 193 nm, where the molecule dissociates (at least the HCN elimination pathways) in the ground electronic state. However, our simulations assume that internal conversion is a fully statistical process, i.e., the HCN elimination channels proceed on the ground electronic state according to RRKM theory, which might not be the case. In future studies it would be of interest to include the photo-prepared electronically excited state(s) in the dynamics simulations. † Electronic supplementary information (ESI) available: Electronic energies, optimized geometries and vibrational frequencies obtained at the MPWB1K/ 6-31+G(d,p) level of theory for the stationary points of the pathways involved in the second set of kinetic calculations. See
Journal of the …, 1999
The reactions of hydrogen isocyanide (HNtC) with various simple alkynes (HCtC-X, with X ) H, CH 3 , NH 2 , F), formally [2 + 1] cycloadditions, have been studied by density functional theory (DFT) with the hybrid exchange correlation B3LYP functional and a 6-311G(d,p) basis set, as well as by MO theory with CCSD(T) calculations. For each reaction, the intrinsic reaction coordinate (IRC) pathway has been constructed. It is shown that each [2 + 1] cycloaddition is nonconcerted but proceeds in two steps: rate-determining addition of HNtC to a carbon atom of HCtCX, giving rise to a zwitterion intermediate, followed by a ring closure of the latter, yielding finally cyclopropenimine. In all cases, HNtC behaves as an electrophile. The activation energies corresponding to both possible initial attacks of HNtC are distinguishable, introducing thus a site selectivity and an asynchronism of bond formation in the initial step, for which a rationalization using DFTbased reactivity descriptors and the local HSAB principle has been proposed. Except for HCtC-F, initial attack on the unsubstituted alkyne carbon is preferred. The hardness and polarizability profiles along the IRC reaction paths of the supersystem have also been constructed. In some cases, there are no clear-cut extrema; in other cases, there is a minimum in the hardness profile and a maximum in the polarizability profile, but these extrema do not coincide with the energy maximum and are rather shifted toward the side having the closest value, following apparently a generalized Hammond postulate. While the higher hardness-lower polarizability criterion seems to hold true, there is no obvious relationship between hardness and energy. The activation energy (E act ) vs hardness difference relationship recently derived by Gázquez turns out to be successful in the interpretation of the calculated E act sequences.
The Journal of Chemical Physics, 2010
We have studied the interaction of CH 4 with Al 2 and Al 3 neutral and charged clusters in the two lowest lying spin states using density functional theory. These calculations, via extended search, are used to determine the stable positions of H and CH 3 near the cluster, and the transition state to break the H -CH 3 bond. In all cases, stable methyl-aluminum-hydrides are possible. The H desorption is studied by means of vibration analysis and application of transition state theory. A common observed trend is that, in breaking the H -CH 3 bond, the interacting H atom is attached to the "surface" of the clusters attracting some negative charge of Ϸ0.2e. The charge transfer is illustrated using the corresponding orbitals near the transition state in conjunction with the computed Mulliken population analysis. Thermal vibrations, generally, do not enhance the reaction. In all exothermic cases, the binding energy toward CH 3 + HAl n charge increases with increasing charge of the original Al n ͑q=−1,0,1͒ cluster. Although Al lacks occupied d-orbitals, the small Al clusters reduce the ͑free methane͒ CH 3 -H dissociation barrier except for Al 3 ͑q=−1,0͒ . The relevant reactions in desorption require ϳ400-700°C.
J Phys Chem a, 1997
C 6 H 7 + has been investigated by using the ab initio method at MP2-FC/6-31G* level and single point calculations on the MP2 geometries at the MP4(SDTQ)-FC/6-31G* level. The most stable structure located corresponds to the benzenium ion C 6 H 7 + in which a proton is bonded to one of the carbon atoms of the benzene ring and an extension of the delocalization has taken place to include the attached proton, the π-electron density distribution being basically allylic in agreement with experimental findings. Two transition structures (TSs) for hydrogen scrambling were found on the C 6 H 7 + PES. The first one corresponds to the peripheral migration of a proton in the benzenium ion and determines an energy barrier of 7.8 kcal/mol at MP2 level (10.8 at MP4//MP2 level) in good agreement with experimental data. The second scrambling TS corresponds to the interchange of the two hydrogen atoms bonded to the same carbon atom in the ring of the benzenium ion and presents an energy barrier of 59.2 kcal/mol at MP2 level (62.6 at MP4//MP2 level). The H 2 -elimination is an endoergic process that proceeds through a very late TS and an intermediate very close in energy to it that finally renders the products, C 6 H 5 + + H 2 , without any energy barrier. The activation energy for this process (70.3 and 70.1 kcal/mol at MP2 and MP4//MP2 levels, respectively) is practically its endoergicity (71.1 kcal/mol at MP2 level and 70.8 kcal/mol at MP4//MP2 level) in accordance with the experimental finding of null energy release as relative motion between the fragments. A configuration analysis of the wave function of C 6 H 7 + along the reaction coordinate for H 2 -elimination clearly shows that the back-donation from the NHOMO of C 6 H 5 + to the LUMO of H 2 plays a fundamental role in the bonding structure of the benzenium ion. The H 2 elimination takes place through deactivation of the back-bonding at an early stage in the process.
Central European Journal of Chemistry, 2009
The reaction mechanism between AlX and HX (X = Br, Cl, and F) have been characterized in detail using DFT as well as the ab initio method. The reaction yielding AlX 3 and molecular hydrogen was calculated to be highly exothermic. The present calculations also show that the possible routes to the trihalides species start more favorable with the primary insertion product AlX 2 H than with the biadduct AlX(HX) 2 one.
We report on ab initio coupled-cluster calculations of the interaction potential energy surface for the HCNH + –He complex. The aug-cc-pVTZ Gaussian basis, to which is added a set of bond functions placed at mid-distance between HCNH + center of mass and He atom is used. The HCNH + bonds length are set to their values at the equilibrium geometry, i.e., r e [HC] = 1.0780 Å, r e [CN] = 1.1339 Å and r e [NH] = 1.0126 Å. The interaction energy presents a global minimum located 266.9 cm −1 below the HCNH + –He dissociation limit. Using the interaction potential obtained, we have computed rotational excitation cross sections in the close-coupling approach and downward rate coefficients at low temperature (T ≤ 120 K). It is expected that the data worked out in this study may be beneficial for further astrophysical investigations as well as laboratory experiments .
Reaction mechanisms of dissociative chemisorption of HI, I2, and CH3I on a magic cluster Al 13−
Journal of Computational Chemistry, 2008
We have investigated the transition-state structures and reaction mechanisms for the dissociative chemisorption reactions of HI, I 2 , and CH 3 I on the magic cluster Al À 13. The HI, I 2 , and CH 3 I molecules approach Al À 13 with an end-on orientation rather than a side-on orientation because of the more effective orbital overlap in the end-on orientation. The reactions of Al À 13 with HI and I 2 would produce Al 13 HIand Al 13 I 2 2 , respectively, because of large exothermic energy changes and relatively small activation energies. The reaction of Al À 13 with CH 3 I is unlikely to take place because of the low mobility of CH 3 on Al À 13 and the high activation barrier for the S N 2-type reaction. The dissociative chemisorption reactions are preferred thermodynamically to the abstractive chemisorption reactions.