Results 1 - 10 of 1764
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[en] At low excitation energies of under 5 eV, conical intersections (CIs) involving the lowest three electronic states of aniline, viz. the and /GS intersections, are accessible. Signatures of ultrafast dynamics, including H atom loss, are observed experimentally with energies above the threshold. Ab initio results corroborate the view that the intersections are involved in the rapid population flow. In the present computational study, we characterize these intersections using the CASSCF and XMS-CASPT2 methods. We locate the CIs and analyse the important vibronic couplings at these geometries from a normal mode as well as an NH2 local mode perspective. Through our findings, we suggest that modes largely local to the NH2 group couple the electronic states the strongest at these intersections.
[en] The nucleophilic substitution reactions of dibutyl chlorophosphate (3) with substituted anilines (XC6H4NH2) and deuterated anilines (XC6H4ND2) are investigated kinetically in acetonitrile at 55.0 .deg. C. The obtained deuterium kinetic isotope effects (DKIEs: kH/kD) are secondary inverse (kH/kD = 0.86-0.97) with the strongly basic anilines while primary normal (kH/kD = 1.04-1.10) with the weakly basic anilines. The DKIEs, steric effects of the two ligands, activation parameters, cross-interaction constants, variation trends of the kH/kD values with X, and mechanism are discussed for the anilinolyses of the nine (R1O)(R2O)P(=O)Cl-type chlorophosphates. A concerted mechanism is proposed with a backside nucleophilic attack transition state for the strongly basic anilines and with a front side attack involving a hydrogen-bonded four-center-type transition state for the weakly basic anilines on the basis of the magnitudes, secondary inverse and primary normal, and variation trends of the kH/kD values with X
[en] Quenching mechanisms of coumarin derivative 6-bromo-3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin (6BDTC) were carried out in different solvents using the steady-state method to understand the role of diffusion in the quenching mechanism. The solute was excited by UV radiation of wavelength 360 nm. Various quenching parameters like frequency of encounter, kd; probability of quenching per encounter, p; and quenching rate parameter, kq, were experimentally determined for all solvents. Activation energies of quenching, Ea, were also determined by using the literature values of activation energy of diffusion, Ed. It was found that the values of Ea were less than Ed in all solvents indicating that the quenching reactions are more significantly influenced by material diffusion. (author)
[en] The aminolysis of phenyl dithiocyclohexane-carboxylates with anilines in acetonitrile proceeds by rate-limiting breakdown of a tetrahedral intermediate, T±. The large βX (βnuc) values can be accounted for by a strong localized cationic charge on the nitrogen atom of anilines in T±, which is lost in the aniline expulsion from T± (k-a). The breakdown rate ratio of k-a/kb is large due to large k-a and relatively small kb. The proposed mechanism is also supported by a large positive cross-interaction constant, ρXZ (= 1.68), adherence to the RSP, and low activation parameters. The greater than unity kH/kD values involving deuterated anilines suggests a four-center type hydrogen-bonded TS
[en] A novel diamine ligand containing a simple thiophene ring in the backbone has been synthesized. Substitution at the nitrogen atoms with either 2,4,6-trimethylphenyl (Mes) or 2,6-diisopropylphenyl (Dipp) was varied via a condensation reaction between the corresponding aniline and 3,4-diformylthiophene, giving two different ligand derivatives. In onwards chemistry that targeted the cyclic diaminochlorophosphines, the substitution at phosphorus was dependent on the ligand used. For example, when a stoichiometric reaction between PCl3 and thiophene-3,4 diyldimethaneamine (R = Mes) was carried out, the synthesis of a bis-substituted diphosphino- product was isolated. If the R = Dipp ligand derivative was employed, both a 2:1 and 1:1 stoichiometric reaction between PCl3 and the diamine was observed. Nevertheless, the cyclic diaminochlorophosphine (i.e., 1:1 stoichiometry) for R = Dipp was isolated in high yields and the synthesis of the corresponding phosphenium cation was achieved and structurally characterized. (author)
[en] In this system hydroquinone is oxidized to pbenzoquinone by H2O2. 2 aniline are added, in successive stages, to pbenzoquinone, to yield the disubstituted quinone as the final product. 20 The UV-VIS spectrum of the product in aqueous solution presented in Figure 1. It is obvious that a strong absorption peak with a maximum at 550 nm is formed. In conclusion, the new method based on the addition product formation has been demonstrated to be reliable and with acceptable sensitivity for the determination of hydrogen peroxide in verities of product.
[en] The nucleophilic substitution reactions of diethyl thiophosphinic chloride with substituted anilines (XC6H4NH2) and deuterated anilines (XC6H4ND2) are investigated kinetically in acetonitrile at 55.0 .deg. C. The values of deuterium kinetic isotope effects (DKIEs: kH/kD) invariably increase from secondary inverse (kH/kD < 1) to primary normal (kH/kD > 1) as the nucleophiles change from the strongly basic to weakly basic anilines. The secondary inverse with the strongly basic anilines and primary normal DKIEs with the weakly basic anilines are rationalized by the gradual transition state (TS) variation from a predominant backside attack, via invariably increasing the fraction of a frontside attack, to a predominant frontside attack, in which the reaction mechanism is a concerted SN2 pathway. A frontside attack involving a hydrogen bonded, four-center-type TS is substantiated by the primary normal DKIEs
[en] Some sterically very bulky salicylaldimine ligands were designed and prepared. In the ligand framework, bulky aryl substituents were installed on the ortho position of the salicylaldimine backbone as well as the ortho position of the aniline moiety. Subsequently, the corresponding zinc complexes were prepared and characterized. The zinc complexes bearing electron-withdrawing and bulky substituents on both positions showed much higher activity and much better controlled behavior in the ring opening polymerization of ε-caprolactone than the complexes bearing sterically less bulkier alkyl substituents. Graphical abstract: .