Theoretical study of nucleophilic addition of amines to organic nitriles

The mechanism of nucleophilic addition of a series of amines to acetonitrile MeC≡N both free and activated in a platinum complex trans-[PtCl₂(N ≡CMe)₂] was studied in detail by the theoretical methods of quantum chemistry. The influence of the nature of a particular nucleophile on the mechanism, kinetic and thermodynamic characteristics of the processes was elucidated. These reactions proceed according to a concerted highly synchronous mechanism that includes formation of 6-membered transition state consisting of the nitrile, amine, and water molecules. Hydrazine, aliphatic amines, and methylendiamine exhibit the highest reactivity from both kinetic and a thermodynamic viewpoint, while aromatic amines and amidine are the most inert.     

Theoretical study of electrophilic versus nucleophilic character of transition metal complexes of phosphinidene

A comparative theoretical study of the terminal phosphinidene complexes HPCr(CO)₅, HPTi(Cp₂) and HPTiCl₂, at the MP2 and DFT levels, has been carried out. The calculated results have then been used for determining the electron localization function (ELF) in these moieties. Both techniques show that in the singlet ground state of HPCr(CO)₅, one gets a weak double P–Cr bond, with an electrophilic character on P (i.e. electron-deficient center). Conversely, in the singlet ground state of Ti complexes, the P–Ti bond shows a greater double bond character than in the P–Cr linkage, associated with an overall nucleophilic character of P. These results are in good agreement with all available experimental data.     

Theoretical study of ammonia nucleophilic addition to nitriles in platinum complexes

The mechanism of the reaction of the ammonia nucleophilic addition to nitriles RC≡N, both free and activated in the platinum complex trans-[PtCl₂(N≡CCH₃)₂], was studied in detail by theoretical quantumchemical methods. The reaction resulting in the formation of free or coordinated amidines proceeds through consecutive formation of an orientation complex, a six-membered cyclic transition state, and a final reaction product, in which an amidine is in the E-configuration. Water containing in a solvent plays a role of a promoter of this process. The activation effect is interpreted from the viewpoint of both kinetic and thermodynamic factors. It was shown that the mechanism of the reaction product E-Z-isomerization includes the deprotonation of the amino-group nitrogen atom, the change of the coordinated ligand conformation, and the protonation of the nitrogen atom.     

Spectroscopic parameters of nucleophilic and electrophilic reactivity

Reactions of a distinct charge transfer nature (exampled by those between N,N-dimethylaniline and N-methyl cations) are associated with charge transfer bands, in the visible, of energy hν = I ? E + C where I is the ionisation energy of the nucleophile, E is the electron affinity of the electrophile and C is a correction term. As an example, the reaction between N,N-dimethylaniline and N-methylacridinium chloride is examined in detail. Tables of I are given for anions in adiponitrile solution and of hν for cations in dimethylaniline/alcohol solution; low values of I correspond with greater nucleophilic activity and low values of hν with greater electrophilic activity.     

A quantum chemical study on electrophilic addition

Non-empirical SCF-MO calculations were carried out on two limiting structures of C₂H₄F⁺, corresponding to the cyclic and open valence tautomers, both of which are possible reaction intermediates of the electrophilic addition reaction of F₂ to CH₂ =CH₂. It was found that both species had thermodynamic stability, corresponding to two distinct minima on the energy surface. However, the 2-fluoroethyl carbonium ion showed a greater stability than the fluoronium ion by about 10 kcal/mole.     

Theoretical study on the regioselectivity of the B80 buckyball in electrophilic and nucleophilic reactions using DFT-based reactivity indices

Density functional theory calculations at the B3LYP/SVP and B3LYP/6-311G(d) levels were carried out for a series of XH(3)B(80) complexes with X = {N, P, As, B, Al}. To probe the regioselectivity of B(80), the electronic Fukui function, the molecular electrostatic potential (MEP), and the natural bond orbital (NBO) were determined. These indices were shown to provide reliable guides to predict the relative reactivities of the boron buckyball sites. Thermodynamic stabilities of the complexes formed by the reaction of B(80) with nucleophiles (NH(3), PH(3), AsH(3)) and electrophiles (BH(3), AlH(3)) are in good agreement with the prediction of regioselectivity indicated on the basis of Fukui and MEP indices. The qualitative results suggest the boron buckyball to be an amphoteric and hard molecule. It has two distinct reactive sites localized on caps and frame, which act as acids and bases, respectively. Most of the complexes are stable with formation energies comparable to that of the analogous complexes of the borane molecule, BH(3)BH(3), BH(3)NH(3), and BH(3)AlH(3). The B-H-B bond characteristics of diborane are recovered in B(80)BH(3). Exohedral complexes are more stable than endohedral complexes. The most stable complexes are those with NH(3) on the caps and BH(3) on the pentagonal ring of B(80).     

Kinetic and thermodynamic stability of cluster compounds under heating

A new polymorphic form of Norfloxacin has been identified and fully characterized by a variety of methods including powder X-ray diffraction, vibrational spectroscopy (IR and Raman), thermal analysis (DSC and TG), SEM and solid-state NMR spectroscopy. The relationship between the new form C and the previously known forms A and B have been studied. Moreover, the crystal structure of the known form A has been solved by single-crystal methods.     

Selenium-catalyzed halolactonization: nucleophilic activation of electrophilic halogenating reagents

Diphenyl diselenide catalyzes the halolactonization of unsaturated acids with N-halosuccinimides under mild conditions. The diselenide not only accelerates the reactions, but in some cases affords regiocontrol in favor of gamma-lactone products. Experiments show that the regioselectivity in favor of gamma-lactones is a result of kinetic rather than thermodynamic control.     

Theoretical study of the effect of substituents on electrophilic addition to olefins: Ab initioMO approach with energy decomposition

The interaction energies of proton with ethylene and substituted ethylenes in a positive bridged ion have been calculated by ab initio MO method with STO -3G basis set, and the energies were further decomposed according to decomposition scheme proposed by Kitaura and Morokuma [Int. J. Quantum Chem. 10 , 325 (1976)].     

Theoretical elucidation of kinetic and thermodynamic control of radical addition regioselectivity

The cyclizations of two structurally similar 2-oxo-5-hexenyl-type radicals have been investigated by ab initio and density functional (UB3LYP/6-31+G**//UHF/6-31G* and UB3LYP/6-31G*//UB3LYP/6-31G*) calculations. The origin of apparently contradictory reports of 6-endo and 5-exo cyclizations is determined. Kinetic control favors 6-endo cyclization, while thermodynamic control gives 5-exo cyclization, and the observation of different products from different research groups arises from the difference in experimental conditions used by the two groups. The outcome of a new cyclization reaction was predicted by using these theoretical techniques. Kinetic control is predicted to yield exclusively the products of 6-endo cyclization, while thermodynamic control would lead to an approximately equal mixture of one 6-endo and one 5-exo cyclized product. Experimental studies revealed that the reaction yields only the products of 6-endo cyclization through kinetic control.     

The electrophilic addition of thiols to olefins: A theoretical and experimental study

Density functional theory with the B3LYP hybrid functional and 6–31G* basis set was used to study the geometric and electronic structure of H₂C = CHR (R = H, CH₃, C₂H₅, C₃H₇, C₄H₉, and C₅H₁₁) olefins, their carbocations formed in the addition of the proton to the olefins, R′-S-H aliphatic thiols (R′ = H, CH₃, C₂H₅, and C₃H₇), the products of the addition of thiols to carbocations, and the final products of the addition of thiols to olefins. The proton affinity of the olefins and the products of the addition of thiols to olefins was calculated. The conclusion was drawn that the limiting stage in the nonradical addition of thiols to olefins catalyzed by acids was proton transfer from the protonated reaction product to the olefin. The theoretical results were compared with the experimental data on the electrophilic addition of polymercaptan to heptene-1.     

News in reactions of electrophilic substitution of organomercury compounds nucleophilic promotion and nucleophilic catalysis

Conclusions The influence of nucleophilic catalysis and nucleophilic promotion in various reactions of electrophilic substitution of organomercury compounds was considered.Report at the General Meeting of the Department of General and Technical Chemistry, Academy of Sciences of the USSR, on December 15, 1965.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 955–963, June, 1966.     

Theoretical study of nucleophilic substitution at two-coordinate sulfur

A series of nucleophilic substitution reactions involving simple species (chloride, phosphide, methoxide, hydroxide, and amide) as nucleophile and leaving group in methylsulfenyl derivatives were examined at B3LYP/aug-cc-pVDZ. The reactions involving hydroxide and amide correspond to deprotonation and not substitution. The substitution reactions follow an addition-elimination pathway, possessing a triple-well potential energy surface. The intermediate along this pathway is of trigonal bipyramid geometry with the nucleophile and leaving group occupying apical positions.     

A cooperative allylic fluorination: combination of nucleophilic and electrophilic fluorine sources

A one step, regioselective allylic fluorination of alkenes is reported in which electrophilic and nucleophilic sources of fluorine act synergistically to afford rearranged allylic fluorides over alternative vicinal dihalides. The reaction occurs under exceptionally mild conditions and without need for prefunctionalization or transition metal catalysts. The fluorination of cyclic alkenes and monoterpenes is highlighted, and preliminary mechanistic experiments reveal that dual (radical and ionic) pathways operate simultaneously.     

Quantum-chemical study of electrophilic addition reaction of iodine to ethylene

The relative stability of and barrier to interconversion of the two possible intermediates in the electrophilic addition of iodine to ethylene have been studied by means of ab initio molecular calculations with pseudopotential approximations. The geometries of the 2-iodoethyl and ethylene iodonium cations have been optimized by the energy gradient technique with pseudopotential approximations. From the results of the calculations, it is found that the only possible intermediate is the cyclic ethylene iodonium ion, as shown by experiments.     

Functionally substituted alkylbenzotriazoles: Reactivity of alkylbenzotriazoles toward electrophilic and nucleophilic reagents

The reactivity of benzotriazolylacetone toward a variety of carbon and nitrogen electrophiles is reported. Several novel azolylbenzotriazoles as well as benzotriazolyl‐cinnolines have been synthesized. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:141–145, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10009