Mechanism of the reaction between diazonium salts and potassium nitrite based on chemically induced dynamic nuclear polarization

Theoretical and Experimental Chemistry -     

Kinetics and reaction mechanisms of diazo compounds and iodonium salts as studied by chemically induced dynamic nuclear polarisation

CIDNP phenomena in various reactions of diazo compounds and iodonium salts are described. The various reaction pathways leading to the formation of polarised aromatic products are analysed in detail.     

Study of the reaction of the superacid HGeCl3 with olefins by the chemically induced dynamic nuclear polarization method

Conclusions In reactions of the superacid HGeCl₃ with 2-methylbutene-2,2,3-dimethyl-2-butene and styrene, leading to hydrogermylation products of the indicated olefins, we have observed chemically induced dynamic nuclear polarization effects which are clear evidence for the presence of radical stages in the reactions.Translated from Izvestiya Akademii Nauk SSSR, No. 7, pp. 1617–1620, July, 1987.     

Transient and stationary nutations in chemically induced dynamic nuclear polarization

Transient nutations are observed in nuclear magnetic resonance during continuous generation of magnetization at and near resonance in reactions leading to chemically induced dynamic nuclear polarization. Modulation of the reaction with the nutation frequency leads to stationary nutations. The phase-sensitive detection of the nutation signals is used to discriminate effects of chemically induced polarization from steady state resonance signals. For single line spectra the effects are quantitatively explained by Bloch-type equations containing magnetization production terms. Experimental results obtained during photochemical reactions of di-tert-butyl ketone demonstrate general applications of the method.     

Intramolecular electron transfer in lysozyme studied by time-resolved chemically induced dynamic nuclear polarization

The kinetics of the chemically induced dynamic nuclear polarization (CIDNP) produced in reactions of hen lysozyme with photosensitizers have been studied for the native state of the protein at pH 3.8 and for two denatured states. The latter were generated by raising the temperature to 80 degrees C or by combining a temperature rise (to 50 degrees C) with the addition of chemical denaturant (10 M urea). Detailed analysis of the CIDNP time dependence on a microsecond time scale revealed that, in both denatured states, intramolecular electron transfer (IET) from a tyrosine residue to the cation radical of a tryptophan residue (rate constant k(f)) is highly efficient and plays a decisive role in the evolution of the nuclear polarization. To describe the observed CIDNP kinetics with a self-consistent set of parameters, IET in the reverse direction, from a tryptophan residue to a tyrosine residue radical (rate constant k(r)), has also to be taken into account. The IET rate constants determined by analysis of the CIDNP kinetics are, at 80 degrees C: k(f) = 1 x 10(5) s(-1) and k(r) = 1 x 10(4) s(-1); at 50 degrees C in the presence of 10 M urea: k(f) = 7 x 10(4) s(-1), k(r) = 1 x 10(4) s(-1). IET does not appear to influence the CIDNP kinetics of the native state.     

Photoinitiated oxidation of NADH catalyzed by horseradish peroxidase studied by chemically induced dynamic nuclear polarization

The photoinitiated oxidation of β-NADH catalyzed by horseradish peroxidase (Per³⁺) was studied by time-resolved photoinitiated chemically induced dynamic nuclear polarization (CIDNP). The polarization observed on protons at the C(4) atom of the β-NADH molecule is evidence for the reversible one-electron transfer between the radical cation NADH^+· and the ferroperoxidase intermediate (Per²⁺). A new approach based on electron transitions in the (NADH^+· Per²⁺) pair was proposed to describe the formation of CIDNP effects in systems including quartet (Q)—doublet (D) electron transitions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1090–1094, July, 2006.     

An investigation of the mechanism of the reation of allyltriethylstannane with bromotrichloromethane by radiofrequency probing and chemically induced dynamic nuclear polarization (CIDNP)

The methods of radiofrequency probing (RFP) and chemically induced dynamic nuclear polarization (CIDNP) have been used to study the mechanism of the reaction of allyltriethylstannane with bromotrichloromethane. The CIDNP effects which have been detected prove the presence of radical stages in this reaction. An assumption has been made about a possible radical pathway for the β-decomposition of elementorganic compounds.     

The creation of off-diagonal elements in chemically induced dynamic nuclear polarization experiments

The nuclear density matrix created in pulsed CIDNP experiments contains off-diagonal elements whenever the resulting nuclear spin system is strongly coupled. These off-diagonal elements, which connect spin states with the same magnetic quantum number, are due to the mixing of nuclear state functions during the process of product formation. The observation of these elements by means of a two-pulse experiment is described.     

Radical pair substitution in chemically induced dynamic nuclear polarization. Co-operative effects

The problem of radical pair substitution in Chemically Induced Dynamic Nuclear Polarization is reconsidered. The singlet—triplet evolution in the radical pairs is described in a continuous fashion, assuming non-disturbance of the electron spin state during the scavenging reaction. The CIDNP effect of the recombination product of the secondary pair is demonstrated to result from the “co-operative effect” of singlet—triplet evolution in both the primary and the secondary pair. The hypothetical one proton case, in which the primary pair has different g-factors and a zero hyperfine interaction, and the secondary pair equal g-factors and a non-zero hyperfine interaction is treated qualitatively. Some examples are discussed in which older models lead to a faulty interpretation of experimental results.     

带取代基二芳基碘 盐直接光解与敏化光解机理的研究

本工作采用瞬态和稳态的方法对带不同取代基碘 盐的直接光解和敏化光解问题进行了研究, 在两种光解过程中, 电子转移均起到重要作用. 在直接光解反应中, 由于开始时生成的带不同取代基的苯衍生物在进一步反应中起到重要作用, 因此它们的光解效率如下: 3>2≥1, 在敏化光解反应中, 由于2-氯代硫杂蒽酮(CTX)作为电子给体参与其中. 因此敏化光解效率和所研究 盐的得电子能力有关, 其次序如下:1>2≥3。     

Palladium-catalyzed cross-coupling of diaryliodonium salts with organotin compounds

M. V. Lomonosov Moscow State University, 119899 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2683–2685, November, 1992.