Transmission of substituent effects via molecular lines of force: defense of the DSP method and an illustration of its use in explaining .pi. polarization

Abstract

thiosulfate react at both electron-deficient sites to varying degrees and afford mixtures of redox and C-substitution products. Aliphatic thiols and disulfides react slightly at the nitrenium ion. There was no evidence for electron transfer to form a radical intermediate. Experimental SectionWeighed samples of 10 pmol (2.5 mg) of analytically pure 3-acetoxyxanthine hydrochloride15 were dissolved in 5 mL of 0.1 M NaH2P04 buffer containing 0.01 M (5 equiv) of the desired nucleophile. Reactions were allowed to proceed in the dark at ambient temperature for 24 h, most of the solvent was removed under reduced pressure, and the solutions were chromatographed over 9 X 150 mm columns containing Dowex 50 (H+) resin. H20 eluted uric acid, 8-thiouric acid, 8-nitroxanthine, 8-(phenylthio)xanthine, and 2 while 0.1 or 1N HC1 eluted 6. Products were identifiable both by their position of elution from the column and by comparison of UV spectral values in acid and base to those of authentic samples or to reported values. Yields were determined from the optical density of measured elution volumes and known e values: 8-nitroxanthine (pH 1), Xm" 360 nm (e 10 600) i59 3-hydroxyxanthine (2; (pH 2-4), xj" 272 nm (t 10000)i60 8-thiouric acid (pH 2), Xm", 303 nm (e 18200);61 xanthine (6; pH 0), XmaT 260 nm (t 9200).15 OD values were determined with a Unicam SP800A (59) J. W.

13C NMR substituent-induced chemical shifts in 4-(substituted phenyl)-3-phenyl-1,2,4-oxadiazol-5(4H)-ones (thiones)

“…The most successful analyses of substituent effects on the chemical shifts have been used Hammett-type applications, using SSP, DSP and DSP-NLR analysis methods. The DSP analysis method extension of the Hammett approach has proven particularly useful [43]. The DSP-NLR analysis method is a successful equation in the modeling of long-range substituent effects, which is derivatives of Hammett equation [44].…”

Application of Gassman-Fentiman tool of increasing electron demand to stable carbocations using nuclear magnetic resonance spectroscopy

“…This was attributed to a phenomenon termed localized "r-polarization effect" wherein a dipole is set up on Z or near a C-Z bond, when Z is an electron withdrawing group (structure 36). The interaction of this dipole through the space of the molecular cavity (partially transmitted via molecular lines of force) [64] was deemed to increase the electron density, as shown (in 36) around the electron deficient center causing shielding of the chemical shifts.…”

Determination of substituent effects by factor analysis and multiple linear regression for the carbon-13 nuclear magnetic resonance chemical shifts in 4-substituted phenols and 2-nitrophenols

“…A number of different procedures have been attempted, including the Swain-Lupton approach (2) and the Hammett analysis (3) using either a single substituent parameter (SSP) or dual substituent parameter (DSP) procedure (4,5). The relative merits of the SSP and DSP scales have been discussed in detail (6)(7)(8)(9). The DSP method, using the correlation of 6 with the field/inductive and resonance substituent constants u, and uRO, has been found to be effective in the determination of the relative contribution from the field and resonance effects (10)(11)(12)(13).…”