Splitting constants

The spin adducts of free radicals and MNP or DMPO were observed by means of an ESR spectrometer. The data of hyperfine splitting constants were compiled in Tables 9 and 10 [40-42,44,45]. ESR studies on the initial free radicals revealed that the monoalkylamino radical RHN-, dialkylamino radical R2N-, and aminomethyl radical -CH2N< or aminoethylidene radical >N( CHCH3) were obtained from the corresponding primary, secondary, and cyclic tertiary amine. In case of a tertiary diamine such as TMEDA, formation of... 

Table 9 Hyperfine Splitting Constants of Spin Adduct Formed APS/Amine/MNP or DMPO System ...

Tabie 10 Hyperfine Splitting Constants of Spin Adducts Obtained from APS/Amine/MNP Systems... 

System Radical trapped by MNP Hyperfine splitting constant (0.1 mT) ap ap a," ... 

The initial radicals formed from the reaction of Ce(IV) ion and reductant systems can be trapped by MNP. The spin adducts of the initial radicals and MNP were observed by means of an ESR spectrometer. The structure of the initial radicals and the hypeiTme splitting constants of the spin adduct of the radical with MNP and tt-phenyl-N-/er/-butylnitrone (PBN) are compiled in Tables 5 and 6, respectively. 

Table 5 HyperTme Splitting Constants of CAN-Reductant-MNP Systems [20,36,38,40]...

Reductant Radical trapped by MNP Hyperfme splitting constant (mT) a N a ... 

Table 6 Hyperfme Splitting Constants of CAN-reductant- PBN Systems [38] ...

Table 3 presents the hyperfme splitting constants of some sulfur-containing aromatic radical anions. The series studied included the monoxides and dioxides of dibenzothio-phene 1, thioxanthene 2, thioxanthone 3, dibenzo[b,/] thiepin 4 and dithienothiophene dioxide 5. 

TABLE 3. Hyperfine splitting constants (gauss) of some sulfur-cpntaining aromatic radical anions obtained in 1,2-dimethoxyethane with K metal as the reductant at — 80 °C... 

TABLE 4. Hyperfine splitting constants (gauss) of thioxanthone S-(mono or dijoxide radical anions as free or tight contact ion-pair ... 

Table 1. The 72-atom model examined by different theoretical methods. The energy differences (AE in kcal/mol) are calculated with respect to the lowest SCF energy. q(Fe) stands for Mulliken population charges on the Fe atoms q(S) and SS(b.i.) are the Mulliken population charges and the bond index for the bridging S atoms, respectively AEq is the calculated Mossbauer quadrupole splitting constant [mm/sec]. The PUHF spin states are those projected from the UHF wavefunction with 5 = 5,. 

PUHF, yield the lowest energies as well as reasonable Mossbauer quadrupole splitting constants, A Jq. 

It can be noticed there are two types of hydrogen atoms atoms 1-5 lying in the molecular plane and atoms 6 and 7 lying out of the plane. Thus, the hyperfine splitting constants (an) cannot be interpreted by means of one relationship, but the expressions... 

Yonezawa and collaborators (99) have reported unrestricted open-shell SCF calculations where the one-center exchange integrals were taken into account their treatment concerned allyl, vinyl, and nitrogen dioxide radicals. The one-center exchange integrals also are involved in the INDO method (85). Here, the following relationship for hyperfine splitting constants holds ... 

The formation of diphenylphosphino radicals on photolysis of triphenyl-phosphine, diphenylphosphine, and tetraphenylbiphosphine has been verified. In the case of the reactions of the phosphines, the radicals were trapped with t-nitrosobutane and the resultant nitroxyl radical [Ph2PN(0)Bu ] was identified by e.s.r. The nitroxyl radical has a small P splitting constant, demonstrating that there is no extensive delocalization onto the phosphorus atom. The e.s.r. spectrum of diphenylphosphino radicals, generated by photolysis of tetraphenylbiphosphine in benzene at 77 K, has been observed. When methanolic solutions of the biphosphine or triphenylphosphine are flash-photolysed, a transient species having Amax = 330 nm and which decays by first-order kinetics (A 4 x 10 s )... 

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