Proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives. FMO analysis of the effect of methyl and benzo substitution

1986 ◽  
Vol 64 (6) ◽  
pp. 1240-1245 ◽  
Author(s):  
Erwin Buncel ◽  
Helen A. Joly ◽  
John R. Jones
Keyword(s):  
Proton Transfer ◽  
Reaction Scheme ◽  
Frontier Molecular Orbital ◽  
Neutral Species ◽  
Ph Profile ◽  
Hydroxide Ion ◽  
Methyl Substitution ◽  
Rate Determining Step ◽  
Alkyl Derivatives ◽  
Conjugate Acid

The rate–pH profile for detritiation from the C-2 position of 1-methylimidazole has been determined in aqueous solution at 85 °C. The profile is consistent with a mechanism involving attack by hydroxide ion on the conjugate acid of the substrate to give an ylid intermediate in the rate-determining step. At higher pH, hydroxide-catalyzed exchange of the neutral species becomes increasingly important. Comparison of the second-order rate constants derived from the rate–pH profiles of imidazole, 1-methylimidazole, benzimidazole, and 1-methylbenzimidazole showed that methyl substitution caused the rate to increase by 2-to 3-fold while benzo annelation increased the rate by 10- to 20-fold. Frontier molecular orbital (FMO) analysis of the reaction scheme for proton transfer from imidazole, benzimidazole, and their 1-alkyl derivatives has been used to explain the rate-accelerating effect of methyl substitution and benzo annelation in these processes.

Iminoacyl Alkyl Complexes of Zirconium Supported by a Ferrocene-Linked Diphosphinoamide Ligand Scaffold

2016 ◽  
Vol 69 (5) ◽  
pp. 555 ◽  
Author(s):  
Nathan R. Halcovitch ◽  
Michael D. Fryzuk
Keyword(s):  
General Formula ◽  
Mechanistic Studies ◽  
Hydrogen Shift ◽  
Alkyl Complexes ◽  
Rate Determining Step ◽  
Zirconium Complexes ◽  
Alkyl Derivatives ◽  
Benzyl Substituent

Zirconium dialkyl complexes of the general formula fc(NPiPr2)2ZrR2 (where fc = 1,1′-ferrocenyl, R = CH3, CH2Ph, CH2tBu, tBu) have been synthesized and characterized via the addition of alkyl lithium or potassium benzyl derivatives to the dichloride complex fc(NPiPr2)2ZrCl2(THF). Addition of 2,6-dimethylphenylisocyanide to these alkyl derivatives generates the corresponding mono iminoacyl alkyl zirconium complexes. On thermolysis, the iminoacyl moiety containing a benzyl substituent undergoes rearrangement to yield a new complex that contains an alkene-amido fragment. Mechanistic studies point to a 1,2 hydrogen shift as the rate-determining step.

The Hydrolysis of Amides in Acid Solutions - A New Kinetic Equation

1976 ◽  
Vol 29 (2) ◽  
pp. 307 ◽  
Author(s):  
CJ Giffney ◽  
CJ O'Connor
Keyword(s):  
Reaction Mechanism ◽  
Kinetic Equation ◽  
Acid Solutions ◽  
Rate Determining Step ◽  
Conjugate Acid ◽  
Hydrolysis Of

A new kinetic equation, based on a reaction mechanism in which water attacks the N-protonated conjugate acid in the rate-determining step, is formulated for the acid-catalysed hydrolysis of arnides. The equation is well fitted by 60 sets of data for hydrolysis of both aliphatic and aromatic amides.

scholarly journals <i>D</i> region ion-neutral coupled chemistry within a whole atmosphere chemistry-climate model

2016 ◽  
Author(s):  
Tamás Kovács ◽  
John M. C. Plane ◽  
Wuhu Feng ◽  
Tibor Nagy ◽  
Martyn P. Chipperfield ◽  
...  
Keyword(s):  
Climate Model ◽  
Negative Ions ◽  
Reaction Scheme ◽  
Solar Proton ◽  
Proton Event ◽  
Test Case ◽  
Neutral Species ◽  
Ion Molecule Reactions ◽  
D Region ◽  
The Impact

Abstract. This study presents a new ion-neutral chemical model coupled into the Whole Atmosphere Community Climate Model (WACCM). The ionospheric D region (altitudes ~ 50–90 km) chemistry is based on the Sodankylä Ion and Neutral Chemistry (SIC) model, a 1-dimensional model containing 306 ion-neutral and ionrecombination reactions of neutral species, positive and negative ions, and electrons. The SIC mechanism was reduced using the Simulation Error Minimization Connectivity Method (SEM-CM) to produce a reaction scheme of 181 ion-molecule reactions. This scheme describes the concentration profiles at altitudes between 20 km and 120 km of a set of major neutral species (HNO3, O3, H2O2, NO, NO2, HO2, OH, N2O5) and ions (O2+, O4+, NO+, NO+(H2O), O2+(H2O), H+(H2O), H+(H2O)2, H+(H2O)3, H+(H2O)4, O3−, NO2−, O−, O2, OH−, O2−(H2O), O2−(H2O)2, O4−, CO3−, CO3−(H2O), CO4−, HCO3−, NO2−, NO3−, NO3−(H2O), NO3(H2O)2, NO3−(HNO3), NO3−(HNO3)2, Cl−, ClO−), which agree with the full SIC mechanism within a 5 % tolerance. Four 3D model simulations were then performed, using the impact of the January 2005 Solar Proton Event (SPE) on D region HOx and NOx chemistry as a test case of four different model versions: the standard WACCM (no negative ions and a very limited set of positive ions); WACCM-SIC (standard WACCM with the full SIC chemistry of positive and negative ions); WACCM-D (standard WACCM with a heuristic reduction of the SIC chemistry, recently used to examine HNO3 formation following an SPE); and WACCM-rSIC (standard WACCM with a reduction of SIC chemistry using the SEM-CM Method). Standard WACCM misses the HNO3 enhancement during the SPE, while the full and reduced model versions predict significant NOx, HOx and HNO3 enhancements in the mesosphere during solar proton events. The SEM-CM reduction also identifies the important ion-molecule reactions that affect the partitioning of odd nitrogen (NOx), odd hydrogen (HOx), and O3 in the stratosphere and mesosphere.

Base hydrolysis of trans-Halogenoamminebis(dimethylglyoximato) (III). Complexes

1969 ◽  
Vol 22 (12) ◽  
pp. 2569 ◽  
Author(s):  
SC Chan ◽  
PY Leung
Keyword(s):  
Equilibrium Constants ◽  
Base Hydrolysis ◽  
Hydroxide Ion ◽  
First Order ◽  
Rate Determining Step ◽  
Rapid Formation ◽  
Pseudo First Order ◽  
Conjugate Bases ◽  
Hydrolysis Of ◽  
Conjugate Base

The disappearance of trans-[Co(LH)2(NH3)X] (LH = dimethylglyoximate ion, X = chloride or bromide) has been studied in aqueous solutions over a range of alkali concentrations at various temperatures. The kinetics were done with excess of hydroxide ion at a constant ionic strength so that pseudo first-order rate constants were obtained in all the runs. The results were interpreted in terms of the rapid formation of a pre- equilibrium species which then reacts in a rate-determining step to give products. The relatively large equilibrium constants support a conjugate-base pre-equilibrium, in which the proton is lost from oxygen, while the relatively low reactivities of the conjugate-bases are consistent with the absence of electropositive electromeric effects. The similarity in the reactivities of the chloro and the bromo conjugate-bases suggests the possibility of an SN2CB mechanism.

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