In basic solution, p-dimercaptobenzene, which is found to have pKa's of 6.0 and 7.7, is rapidly oxidized by azide radical (k = 7.4 X lo9 M-' s-l) top-benzodithiyl radical anion, the sulfur analog ofp-benzosemiquinone radical anion. This radical has very strong absorption bands at 390 and -700 nm. In acidic solutions, CO2'-abstracts a S H hydrogen atom (k = 3.1 X lo9 M-l s-l) to form thep-mercaptophenylthiyl radical, which has absorption maxima at 350 and 585 nm and a pKa of 2.7. From measurements of its electron-transfer equilibrium with the resorcinol dianion, the reduction potential of the dithiyl radical has been determined to be 0.33 V vs SHE. This value is 0.37 V below the reduction potential of phenylthiyl radical, indicating that resonance stabilization of -36 kJ/mol results from delocalization of the unpaired spin between the two sulfur atoms. This stabilization energy is, however, -39 kJ/mol less than that for the analogous difference of 0.78 V between the reduction potentials of p-benzosemiquinone anion and phenoxy radicals. At high pH, the dithiyl radical anion decays rapidly in second-order processes (2k = 2.8 X lo9 M-l s-I), in contrast to the relatively stablep-benzosemiquinone radical anion, which, because its reduction potential is below that of quinone, is stable toward disproportionation by electron transfer. htroductioaA recent publication from this laboratory3 on the resonance Raman spectrum of phenylthiyl radical (CaHsS') points out interesting differences between its structural features and those of its oxygen counterpart, the phenoxy radical (C6HSO*). In particular, the Raman data show that the CS bond in phenylthiyl radical has substantially less double-bond character than does the CO bond in phenoxy radical, indicating that in the former case the unpaired spin population is largely localized on the sulfur atom. In view of this difference, a comparison of thespectroscopic and chemical properties of the radicals derived from 1,4-dimercaptobenzene (PDMB) with their oxygen analogs, p-benzosemiquinone radical and its anion, is expected to be of considerable interest. This paper reports the results of a pulse radiolytic investigation of the spectra and chemical properties of the p-mercaptophenylthiyl (HSC6H4S*, PMPT') and pbenzodithiyl anion radicals (C6H&*-, PBDT'-). Of particular importance is the reduction potential of the latter (0.33 V vs SHE) which indicates that resonance stabilization is considerably less than that in the case of p-benzosemiquinone anion radical (CsH402*-), where the reduction potential is 0.31 V lower. Background information on the ionization equilibria of the parent compound is also reported. Experimental SectionPulse Radiolysis Studies. Pulse radiolysis studies were carried out at the Radiation Laboratory LINAC facility by standard methods as previously des~ribed.~ Doses of -500 rad ( 5 Gy), calibrated with the N20 saturated thiocyanate dosimeter,s produced an initial radical concentration of -3 pM, Solutions were purged and saturated with nitrous oxide to convert ea...

ESCA core line spectra have been obtained for uracil, the thiouracils, and some 1-methyl and 3-methyl analogues. In addition, anionsof the mono methyl derivatives have been prepared and studied. Core line binding energy shifts for all solid compounds, ionic and neutral, are found to correlate reasonably with CNDO/2 charge distributions calculated for the free molecules. The correlation line for ionic molecules is offset from that for neutrals by a constant factor ascribed to an intermolecular potential term. Specific effects of methylation, thionation, and ionization on the charge distribution are described. Methylation at either nitrogen leads to electron release from the nitrogen into the ring. Thionation results in a decrease in the charge at the site of thionation, while the electron density at adjacent atoms increases. The alterations in charge density are somewhat different for neutral and ionic compounds. Upon ionization of either N(1) or N(3) sites, much of the residual charge is located on the keto oxygens. The presence and position of the thionated carbon during ionization mainly affects the change in electron density at the C(6) position.

13C nmr chemical shifts have been recorded for a number of uracil, thiouracil, and pyrimidine derivatives. These data are discussed in relation to what is known of the lactam–lactim tautomerism in such systems and possible correlations of chemical shifts with normal aromatic substituent chemical shift parameters. The chemical shifts for the CH3 groups in simple methylated derivatives of uracil are very characteristic of the site of methylation and should prove useful as a tool for assigning structures to alkylated derivatives of this general type.

The effects of structural changes on the rates of hydrolysis of a series of chlorothionoformate esters and the analogous chlorodithioformate esters have been studied. For both classes of compound, the reactivity is enhanced by increased electron donation by the hydrocarbon group. These results, the activation parameters for the hydrolyses of the methyl compounds, and the solvent isotope effect are shown to be consistent with the operation of the SN1 mechanism.Les elTets de modifications structurales sur les vitesses d'hydrolyse d'une serie d'esters chlorothionoformates et d'esters chlorodithioformates analogues, ont ete etudits. Pour les deux classes de composes, la rtactivite est accrue si l'on augmente le pouvoir donneur d'tlectrons du groupe hydrocarbure. Ces resultats concernant les parametres d'activation pour les hydrolyses des composes methylts et I'elTet isotopique du solvant, sont consistants avec l'intervention d'un mecanisme SN1.Canadian Journal of Chemistry, 50, 1401Chemistry, 50, (1972 Introduction Previous studies (1-3) have established that chloroformate esters (1 ; X = Y = 0 ) and chlorothiolformate esters (1 ; X = S, Y = 0 ) hydrolyze much more slowly than other acid chlorides, a feature that is most reasonably attributed to initial state conjugation, 2. This effect is enhanced by structural changes that increase electron donation by the hydrocarbon group (R) (3,4) and is diminished in compounds where the hetero-atom (X) has only a limited tendency to use its unshared electrons for n-bond formation. Thus, chloroformates are much less reactive than their thio analogues (3).

13C nmr data have been obtained for a series of 2- and 4-pyrones and pyridones, and their sulfur-containing analogues. Correlations have been observed between the nature of the ring hetero-atom and the chemical shift difference (Δδ) for the Cα and Cβ carbons in these conjugated systems. No significant correlation, however, appears to exist between the chemical shifts of the C=O and C=S groups. Substituent chemical shift (s.c.s.) effects for various simple substituents are compared with those in related series of compounds.