I. N. Rozhkov

Electron structure and reactivity of organofluorine compounds. 3. Mndo and ami calculations of the ground state of perfluoroalkyl chlorides, bromides, and iodides

The semiempirical quantum chemical MNDO and AMI methods were used to determine the equilibrium geometries and electron properties of molecules of perfluoroalkyl halides (RFX): CF3X, CF3CF2X, (CF3)2CFX, (CF3)3CX for X=Cl, Br, and I. It was determined that the effective charge on the Cl atom in RFCl is negative, positive on the I atom in RFI, and depends on RF for the Br atom in RFBr. The CF3 group can act as either an electron acceptor or donor in various perfluoroalkyl halides. The strongest Cα−I bond in the perfluoroalkyl halides occurs with a tertiary RF group.

Electron structure and reactivity of organofluorine compounds. 4. AMI calculations of anion radicals of primary, secondary, and tertiary perfluoroalkyl chlorides, bromides, and iodides

Calculations were carried out using the semiempirical quantum chemical AMI method for anion radicals (AR) of the perfluoroalkyl halides (RFX): CF3X, CF3CF2X, (CF3)2-CFX, and (CF3)3CX for X=Cl, Br, and I. All the ARs studied are thermally stable. The electron affinity of the perfluoroalkyl halides, and consequently, the thermal stability of their ARs increases in the series from F-methyl to F-tertbutyl halides and from the chlorides to bromides and iodides. During formation of an AR the spin density is preferentially localized on the σ* orbital of the Cα−X bond which leads to an increase in the distance between these atoms. Dissociation of the AR of tert-perfluorobutyl iodide to a perfluorocarbanion and an I atom is thermodynamically more favorable than dissociation with formation of a perfluoroalkyl radical and I−.

Reduction potential and relative electron affinity as reactivity indexes perfluoroalkyl halides

Abstract Reduction potentials of perfuoroalkyl halides (R F X) on Pt in CH 3 CN have been determined (E 1 2 , V, SCE) : The values of the relative electron affinity (REA) of R F X were determined as the enthalpy of the reaction (ΔH) : To define ΔH we performed the quantum chemical AM1 calculations of the heats of formation for all participants of the above reaction (R F X and corresponding radical anions). The REA (kcal/mol) are : In accordance with their RP and REA Values, perfluoroalkyl halides may be arranged in the following row which is in a good agreement with their reactivity in SET initiated reactions: (R F ) 3 CJ > (R F CBr > (R F ) 2 CFJ > R F CF 2 J ⋍ (R F 2 CFBr ⋍ (R f ) 3 CCl

New pathway of perfluoroalkyl halide radical anions dissociation

Abstract Two different pathways for dissociation of perfuoroalkyl halide radical anions were proposed on the basis of quantum-chemical calculations (method AM1 with completely optimized geometry) of the enthalpies (ΔH1 and ΔH2). The dissociation pathway is determined by a relation of the electron affinities of RF. and X.. In the gas phase, any RFJ? dissociates with F-carbanion formation: (CF3)3CJ ΔH1=64.9 and ΔH2=5.2 kcal/mol. However the high energy of halide solvatation (particularly for Br- and Cl- may change the correlation between ΔH1 and ΔH2 in solvents and turn the reaction to the ‘radical’ pathway. Thus F-tret.hexyl iodide does not add to the hexene double bond in the presence of electron donor (Zn) in EtOAc at 30° and yields F-alkene only. On the contrary, F-tret.hexyl bromide readily adds to hexene double boud under the same conditions with high yield. This result supposes the ‘radical’ pathway for the dissociation.

Addition of tert-perfluoroalkyl bromides at a multiple bond, initiated by electron transfer

The thermodynamics of the dissociation of the radical-anions of perfluoroalkyl halides was determined by quantum-chemical methods. The conditions for the addition of tertiary perfluoroalkyl bromides to alkenes, initiated by electron transfer, were obtained.

Electronic structure and reactivity of organofluorine compounds: 1. Electronic structure of fluoroethylenes on the basis of quantum-chemical calculations by the MNDO and STO-3G methods

It was established on the basis of MNDO and STO-3G quantum-chemical calculations of fluoroethylenes that the fluorine atom at the vinylic position greatly stabilizes all theσ-MOs of the molecule on account of the accepting induction effect. The absence of additional stabilization of theπ-MO is due to the antiphase overlap of the free pair of the fluorine atom and theπ-MO. The concept of the “electronic depletion of the double bond” in fluorinated olefins is not confirmed by the calculations.

New approach to perfluoroalkly halides chemistry. Interaction of RFX with unsaturated hydrocarbons as a set-process

Abstract The sharp increase of electron affinity and the corresponding rise of oxidative properties of perfluroalkyl halides as compared with unfluorinated analogues have been demonstrated by means of polarography and quantum-chemical calculations. Tertiary perfluoroalkyl iodides possess a rather strong oxidative ability associated with a very high speed of intermediate anion radical dissociation. F-tret.hexyl iodide (1) does not react with unsaturated at 80°. However in the polar solvents (DMF), single electron transfer (SET) occurs at the interaction of (1) with C 6 H 6 or with and F-alkene and/or monohydroalkane are produced. In less polar solvent (EtOAc, 80°) iodide (1) readily adds to alkenes, butadiene and acetylene. The relatively mild conditions for these addition reactions allow to propose the realization of the SET-process in the case of non-polar solvents with the formation of the intermediate contact ion-radical pair. In polar solvents SET-process takes place through the distance with the formation of completely separated radical ions.

Electronic structure and polarographic reduction potential of fluorolefines

Abstract F-Alkenes have the relatively high electron affinities and consequently rather readily undergo electrochemical reduction on Hg in aprotic solvents. The main factor determining the magnitude of reduction potential (RP) of F-alkenes is a quantity of the electron-withdrowing perfluoroalkyl- groups at the double bond: a) CF 2 CF 2 undergoes reduction at the potential more cathodic than −3.0 V (SCE); b) the RP of terminal F-alkenes CF 2 CFR F lie in the region of −2.6 V; c) two R F -groups at the double bond both for terminal and internal F-alkenes fall the RP magnitude to −2.2 V; d) the further increase of the quantity of R F -groups leads to the more sharp downfall of RP (0.8 V per every additional R F -group approximately) and F-tetramethylethylene has RP = −0.6 V. The RP of internal F-alkenes does not change noticeable if vinylic fluorine atoms are substituted by hydrogen whereas a vinylic chlorine reduces the potential on 0.45 V. The RP of F-cyclo-alkenes depends on the cycle cize increasing from six- to four-membered ring. MNDO calculations were performed for the energies of LUMO and HOMO levels and the formal charge distributions in ground states of wide range of F-alkenes. The LUMO level appears to be the π-antibonding orbital for all investigated F-alkenes including also chlorine-containing ones. The π*-δ* levels gap for perfluoroalkenes exceeds 2.3 eV, whereas for chlorine-containing F-alkenes this magnitude decreases markedly to 0.3 eV. The linear correlation for the RP and LUMO levels of F-alkenes was established. At the same time the formal positive charge on sp 2 -hybridized carbon atom at the double bond does not determine the RP value. Moreover on the base MNDO calculations the increase of the quantity of R F -substituents at the double bond unexpectedly decreases the formal positive charge on sp 2 -carbon atom.