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The reaction between isatin and 2,5-dimethoxyaniline is described. The main product was identified as 3,3-bis(4-amino-2,5-dimethoxyphenyl)-1,3-dihydroindol-2-one. The antioxidant activity of the compounds isolated was evaluated with two methods. Three published antitumor E-3-(2-chloro-3-indolylmethylene)1,3-dihydroindol-2-ones entered the same tests to search whether they are endowed with antioxidant activity too. 3,3-Bis(4-amino-2,5-dimethoxyphenyl)-1,3-dihydroindol-2-one and the three antitumor agents showed a good chemical antioxidant activity.

The capacity of human lactobacilli and bifidobacteria to produce metabolites under conditions that may prevail in the human intestine has been studied "in vitro". However, the effect of systematic probiotic consumption on human metabolic phenotype has not been investigated in faeces. This paper shows the potential for the use of (1)H Nuclear Magnetic Resonance ((1)H NMR) spectroscopy for studying the changes of the metabolic profiles of human faecal slurries. Faeces of 16 subjects, characterized by different natural levels of lactobacilli and bifidobacteria were recovered before and after 1 month of supplementation with a synbiotic food based on Lactobacillus acidophilus, Bifidobacterium longum and fructooligosaccharides, and analyzed by (1)H NMR. Multivariate statistical approach has been applied to the data obtained and particularly Canonical Discriminant Analysis of Principal Coordinates (CAP). More than 150 molecules belonging to short chain fatty acids, organic acids, esters, alcohols and amino acids were detected and quantified in the samples considered. The number and the extent of these molecules in faecal slurries were strongly affected by the synbiotic food consumption and gave rise to characteristic metabolic signature. In particular, the short chain fatty acid concentrations significantly increased while the amino acids contents decreased. The comparison of the data indicated that the intake of the synbiotic food alters the host metabolism in a measure dependent on the initial level of lactobacilli and bifidobacteria detected in the faecal specimens. The analysis of (1)H NMR profiles with CAP allowed a separation of faecal samples of the subjects on the basis of the synbiotic food intake. The multivariate statistical approach used demonstrated the potential of NMR metabolic profiles to provide biomarkers of the gut-microbial activity related to dietary supplementation of probiotics.

Ethylenediamine-N,N′-bis(o-hydroxyphenylacetic) acid (o,o-EDDHA) is widely used in commercial formulations as a Fe3+ chelating agent to remedy iron shortage in calcareous and alkaline soils. Commercially available o,o-EDDHA−Fe3+ formulations contain a mixture of EDDHA regioisomers (o,p-EDDHA and p,p-EDDHA), together with other, still uncharacterized, products. NMR spectroscopy can be applied to their study as long as iron is accurately removed prior to the observation. This paper shows that it is possible to obtain a deferrated solution of the organic ligands present in commercial fertilizers containing the EDDHA−Fe3+ chelate by treating the chelate with ferrocyanide, thus forming Prussian Blue that can be easily removed by centrifugation. This iron removal process does not cause significant losses of the o,o-EDDHA ligand or its minor structural isomers.

In the last few years the poultry industry has seen a significant deterioration in meat quality properties during the summer season. The objective of this study was to evaluate the seasonal effect (summer and winter) on turkey meat quality assessed by both conventional and low-resolution nuclear magnetic resonance (LR-NMR) analysis. Eighty-eight breast muscle samples (35 winter and 53 summer) from BUT-Big 6 turkeys belonging to 16 different flocks, were randomly collected from a commercial processing plant. The samples were analysed for transverse relaxation times (T2) by LR-NMR and for initial pH (15 min post mortem), ultimate pH (24 h post mortem) and pH after cooking, temperature at 15 min post mortem, water-holding capacity (WHC, drip loss, filter paper press wetness and cooking loss) at 24 h post mortem, colour of raw and cooked meat and chemical composition (moisture, lipids and proteins). The results indicate that, during the summer season, turkey breast meat undergoes a relevant WHC decrease. Cluster analysis of the raw LR-NMR data evidenced the presence of two groups corresponding to samples harvested in each different season. Correlations between the LR-NMR signal and the conventional parameters measuring WHC were obtained by a recently proposed type of principal component regression (PCR) termed relative standard deviation PCR. Copyright © 2004 Society of Chemical Industry

Many different ways have been devised over the years for analysing phospholipids in solution by 31P NMR. One promising method entails the use of the so-called CUBO solvent, a ternary mixture of dimethylformamide, triethylamine and guanidinium hydrochloride. As this interesting system seems to have been overlooked in the literature, we present here a study on the quantification of phospholipids and lysophospholipids contained in 10 samples of commercial lecithin using the CUBO/31P NMR method. Cluster analysis and principal component analysis of the NMR data showed clear differences among the samples according to the actual lecithin producer. Multivariate analysis of the chemical and physical parameters of the samples confirmed these differences. Copyright © 2004 Society of Chemical Industry

The exceptional efficiency of the iron chelate of ethylenediaminedi(o-hydroxyphenyl)acetic acid (o,o-EDDHA) in correcting iron chlorosis in plants and the medical applications of various metallic chelates of this compound have long been recognized. As commercial preparations of o,o-ADHA usually contain impurities, a method for their detection is proposed. By using one- and two-dimensional nuclear magnetic resonance two impurities were identified. The structure of one of these compounds was assigned to an isomer of EDDHA containing at least one p-hydroxyphenyl moiety. The structure of the other impurity was tentatively assigned to a byproduct the EDDHA synthesis: 2,6-di[CH(COOH)NHCH2CH2NHCH(COOH)Ar]phenol (Ar = hydroxyphenyl). Both compounds were also detected in the ADHA extracted from a commercial iron fertilizer.

NMR spectroscopy is more and more used in the evaluation of food quality, although all its potentialities have not been yet exploited. Paramagnetic metal ions, either naturally present or added to foodstuff, provide an additional source of information that can help to characterize the food. The presence of “paramagnetic” signals in spectra of complicated systems is extremely helpful for their interpretation and provides information otherwise not obtainable. In complex mixtures, NMR spectra are diagnostic, for example, for the oxidation and spin states of iron porphyrins in myoglobin and hemoglobin, yielding information about the metal ion coordination sphere. In turn, the latter determines the extent to which paramagnetism affects the relaxation rates of those water molecules that are able to bind protein sites in proximity of the heme pocket; the relaxation enhancement is then transmitted to the bulk water molecule by chemical exchange. Some possible exploitations of the paramagnetic effect in food science will be suggested, hoping that their use, already successful in structural biology, will soon bring to meaningful results in the food area.

The title compounds (EtOS−SNR2) display diastereotopic OCH2 hydrogens below room-temperature owing to the existence of two stereolabile enantiomers brought about by the restricted S−S rotation in the adopted gauche conformer. A second dynamic process, which makes the N-bonded alkyl groups diastereotopic, was also observed at a much lower temperature (below −80 °C). On the basis of experimental observations and of ab initio calculations, the latter has been interpreted as due to the restricted rotation about the S−N bond. Line shape analysis of the variable temperature 1H and 13C NMR spectra allowed the free energies of activation to be determined for both motions in the case of R = Me, Et, Pri.

The structure of dialkoxy disulfides ROSSOR has been established by single-crystal X-ray diffraction of 1, ArCH2OSSOCH2Ar (Ar = 4-nitrophenyl). The gauche conformation (OSSO dihedral angle = 85.4°) observed in the solid state entails the existence of M and P enantiomers that were actually detected in solution, in the case of MeOSSOMe, t-BuOSSOBu-t, and t-BuOSSOMe (3, 4, 5, respectively), by means of NMR spectroscopy in a chiral environment. The activation parameters (ΔG⧧, ΔH⧧, and ΔS⧧) for the stereomutation of this type of enantiomers, brought about by the S−S bond rotation at high temperature (50−110 °C), were measured by computer line shape simulation of the dynamic NMR spectra of appropriate derivatives bearing alkyl substituents with potentially diastereotopic geminal groups. The free energies of activation for such a process (18−19 kcal mol-1, depending on the compound) were found to be much higher than for the corresponding disulfides (RSSR), owing to the larger S−S double-bond character, as indica...

The addition of several photochemically generated aryl and fluoroalkyl radicals to fullerene C70 was studied by electron spin resonance and the results were compared with those obtained with C60. While simple alkyl radicals afford only three of the five expected RC70• regioisomers, the more reactive aryl and fluoroalkyl radicals give rise to four, except for the trifluoromethyl radical which yielded for the first time the ESR spectra of all five expected isomers. Semiempirical MO calculations and density functional theory calculations were carried out for HC60• and for the five HC70• regioisomers as models for the corresponding alkyl, aryl, and fluoroalkyl analogs in order to describe the unpaired electron distribution in these radical species and as an aid in the assignment of the observed spectra to specific RC70• regioisomers.

Photolysis of dialkoxy disulfides ROSSOR (R = Me, Et, i-Pr, t-Bu, i-PrCH2, t-BuCH2) yields the radicals RO•, ROS•, and ROS•O that were identified on the basis of product analysis and spin trapping techniques. It has been shown that only the alkoxy radicals RO•, produced from ROSSOR, add to the sphere of fullerene C60 in steady state conditions to yield the RO−C60• adducts which can be detected by ESR spectroscopy. The different trend of the hydrogen splitting constants in the RO−C60• with respect to the corresponding RS−C60• adducts previously reported has been interpreted as a consequence of the different C−O and C−S bond lengths.

The addition of several photochemically generated organic radicals (H[sup [sm bullet]], CH[sub 3][sup [sm bullet]], C[sub 6]H[sub 5][sup [sm bullet]], CF[sub 3][sup [sm bullet]], and C[sub 2]F[sub 5][sup [sm bullet]]) to ellipsoidal C[sub 70] was studied by electron spin resonance. Three of the five possible isomers of RC[sub 70] were detected with R = H, CH[sub 3] and four with R = C[sub 6]H[sub 5], CF[sub 3], C[sub 2]F[sub 5]. Arguments based on relative abundances and on comparisons of hyperfine interactions and g factors of the RC[sub 70] isomers and of their C[sub 60] analogs allowed to place the isomers in homologous series and to identify the sites of radical addition on the C[sub 70] surface leading to each isomer. 30 refs., 4 figs., 1 tab.

Substantial equivalence is a key concept in the evaluation of unintended and potentially harmful metabolic impact consequent to a genetic modification of food. The application of unsupervised multivariate data analysis to the metabolic profiles is expected to improve the effectiveness of such evaluation. The present study uses NMR spectra of hydroalcoholic extracts, as holistic representations of the metabolic profiles of grapes, to evaluate the effect of the insertion of one or three copies of the DefH9-iaaM construct in plants of Silcora and Thompson Seedless cultivars. The comparison of the metabolic profiles of transgenic derivatives with respect to their corresponding natural lines pointed out that the overall metabolic changes occur in the same direction, independent of the host genotype, although the two cultivars are modified to different extents. A higher number of copies not only produces a larger effect but also modifies the whole pattern of perturbed metabolites.

This study investigated mass transfer and water state changes promoted by osmotic dehydration on two kiwifruit species, Actinidia deliciosa and Actinidia chinensis. Osmotic treatment was performed in a 61.5% w/v sucrose solution at three different temperatures (25, 35 and 45 °C), with treatment time from 0 to 300 min. Treatment time positively influenced kiwifruit water loss and solid gain while temperature significantly affected only water loss. Peleg’s model highlighted that the main response differences between the two species occurred during the initial phase of the osmotic treatment. Thermal properties and relaxation time measurements offered a complementary view concerning the effects of osmotic dehydration on kiwifruit. DSC parameters appeared to be sensitive to water and solid exchange between fruit and osmotic solution. LF-NMR proton T2 revealed the consequences of the water– solid exchange on the cell compartments, namely vacuole, cytoplasm plus extracellular space and cell wall. During the osmotic treatment, the initial freezing temperature and the freezable water content decrease was dependent on time and treatment temperature, showing a similar tendency for both the kiwifruit species. They evidenced the same treatment response also concerning the reduction of vacuole and the increase of cytoplasm plus extracellular space T2 values.

Conventionally, the analytical procedure can be restricted to the identification and quantification of a selected number of pre-defined metabolites in a biological sample. This process is called metabolite profiling (or, sometimes, metabolic profiling). 2 For example, pre-defined metabolites may belong to a class of compounds (such as polar lipids, isoprenoids, or carbohydrates), or be narrowed down to members of particular pathways. The term metabolite profiling is frequently used in the specific context of drug research in the description of catabolic degradation of an applied chemical. Conversely, the approach revealing the comprehensive metabolome of the biological system under investigation should be called metabolomics. Metabonomics is a further specialization of the omics approach, which is based on the systematic profiling of metabolite levels, but encompasses the systematic and temporal changes of the metabolome in whole organisms occurring in response to diet, lifestyle, environment, etc. 3

The authors studied the addition of alkylthio and alkoxy radicals to C{sub 60} fullerene. The reactions were driven by photoactivation using the emission from a xenon or mercury lamp. ESR was used evaluate the progress and the products of the reactions. 18 refs., 3 figs., 1 tab.

Photolysis of alkyl thiols (RSH) in alkaline solutions yields the corresponding disulfide radical anions (RSSR .- ) whine EPR spectra can be detected over a large temperature range. When mixtures of two different thiols are photolyzed (RSH and R'SH) each of the three possible disulfide radical anions are observed, i.e., RSSR .- , R'SSR .- , and R'SSR' .- . In the case of the allylthiol (CH 2 =CH 2 -SH) both the corresponding disulfide radical anion and the thioaldehyde radical anion (CH 2 =CHCH=S .- ) are simultaneously obtained, the latter exhibiting two rotational conformers due to the restricted rotation about the C-CS bond

The analysis of the NOE effects based upon the interproton distances obtained by MM2 calculations yields a quantitative assessment of the conformer population of 1- and 2-naphthaldehydes (Z-conformer 85% and 12% respectively).

The photochemical reaction of the only isolable aromatic thioaldehyde ArCHS (1; Ar = 2,4,6-tri-tert-butylphenyl) in alkaline medium yields ArCH2CH2Ar (2), ArCH2SCH2Ar (3), 6,8-di-tert-butyl-3,4-dihydro-4,4-dimethyl-1H-2-benzothiine (4) and ArMe (5). A radical mechanism which accounts for the formation of these compounds is proposed, mainly on the basis of the direct observation (EPR spectroscopy) of a number of radicals such as ArCHS˙–(A), ArCHCH2Ar (B), and ArCH2˙(D). Results of scrambling of deuterium atoms confirmed the structure of these radicals through interpretation of the corresponding EPR spectra.

Photolysis of alkylthiols (RSH) in EtOH/EtOK in the presence of ButOOBut yields the disulfide radical anions RSSR˙– in conditions suitable for EPR detection in solution over a wide temperature range.

The addition of several photochemically generated aryl and fluoroalkyl radicals to fullerene C70 was studied by electron spin resonance and the results were compared with those obtained with C60. While simple alkyl radicals afford only three of the five expected RC70• regioisomers, the more reactive aryl and fluoroalkyl radicals give rise to four, except for the trifluoromethyl radical which yielded for the first time the ESR spectra of all five expected isomers. Semiempirical MO calculations and density functional theory calculations were carried out for HC60• and for the five HC70• regioisomers as models for the corresponding alkyl, aryl, and fluoroalkyl analogs in order to describe the unpaired electron distribution in these radical species and as an aid in the assignment of the observed spectra to specific RC70• regioisomers.

Low-temperature photolysis of ArCH 2 OH derivatives (Ar=2- and 3-furyl and -thienyl) in the presence of Bu t OOBu t yields the corresponding ArCHOH radicals which can be observed by means of EPR spectroscopy. Each radical displays E and Z rotational conformers due to restricted a Ar-C α rotation. The study of ArCHOMe radicals, as well as of 2-furyl- and 2-thienylhydroxymethyl radicals having a methyl group in position 3 of the ring, allowed us to identify the most stable of the two conformers

The analysis of the NOE effects based upon the interproton distances obtained by MM2 calculations yields a quantitative assessment of the conformer population of 1- and 2-naphthaldehydes (Z-conformer 85% and 12% respectively).

NOE measurements, combined with MM-2 calculations, predict that the proportion of the Z conformer in the title compound is high enough (14% at room temperature) as to give line broadening effects due to E,Z exchange. Line shape analysis of the dynamic C-13 NMR signals at variable temperature yielded a free energy of activation of 8.3 Kcal/mol. One of the lines of the spectrum of the Z conformer was also directly observed (0.8% at −140°C, corresponding to 11% at room temperature if the entropy difference is assumed zero). ESR spectra and INDO calculations show that also the σ-radical (obtained by H-abstraction from the HCO moiety of the title compound) essentially adopts the E conformation.

The sodium and potassium radical ion pairs of 2,4,6-tri-tert-butyl thiobenzaldehyde and of its ring-deuterated analog have been generated in ethereal solutions and studied by means of electron spin resonance spectroscopy. From the magnitude of the 13C hyperfine splitting it has been inferred that in this radical anion the deviation of the aromatic ring from coplanarity with the CHS plane is smaller than that in the diamagnetic precursor. The solid-state spectrum of the deuterated species has also been interpreted and the g and proton hyperfine tensors have been determined.

In the present work we have succeeded in measuring the OCH 2 rotational barrier in ArOCH 2 radicals and have found experimental evidence for a second restricted motion which is rotation about the Ar−O bond

Hydration of freeze-dried chicken breast meat was followed in the water activity range of aw = 0.12 – 0.99 by a multianalytical approach comprising of sorption isotherm, differential scanning calorimetry (DSC), and nuclear magnetic resonance (NMR). The amount of frozen water and the shape of the T2-relaxogram were evaluated at each water content by DSC and NMR, respectively. Data revealed an agreement between sorption isotherm and DSC experiments about the onset of bulk water (aw = 0.83–0.86), and NMR detected mobile water starting at aw = 0.75. The origin of the short-transverse relaxation time part of the meat NMR signal was also reinvestigated through deuteration experiments and proposed to arise from protons belonging to plasticized matrix structures. It is proved both by D2O experiments and by gravimetry that the extra protons not contributing to the water content in the NMR experiments are about 6.4% of the total proton NMR CPMG signal of meat.

The most effective remedy for iron deficiency is the use of synthetic iron chelates, specifically chelates derived from polyamine-carboxylic acids as EDDHSA (N,N'-ethylenediamine-di-(2-hidroxy-5-sulfophenylacetic) acid). A gradient ion-pair chromatographic method was developed to quantify the total amount of chelated iron in EDDHSA/Fe-3divided by fertilizers. Two mobile phases were used containing. respectively, 35 and 75% acetonitrile in a 0.005 M tetrabutylammonium hydroxide aqueous solution at pH 6.0. The stationary phase was a reverse phase C-18 column (150 mm x 3.9 mm i.d., dp = 5 mum). Two chromatographic peaks appeared and were identified by Electrospray Mass Spectrometry. The first peak corresponds to the monomer of EDDHSA/Fe-3divided by and the second peak has been assigned to condensation molecules. Quality parameters indicate that the method is suitable for the quantification of iron chelate by EDDHSA fertilizers.

A quantitative analysis of NMR proton relaxation in hen egg albumen and yolk is undertaken to research the causes of quality loss during the first few days of storage and to access the feasibility of an on-line NMR sensor of internal egg quality. It is shown that the change in the transverse relaxation in thick egg albumen mainly results from an increase in proton exchange rate resulting from a pH increase attributed to loss of carbon dioxide by diffusion through the eggshell. The results suggest that the low-field T1 is the best relaxation time indicator of albumen quality.

The authors report ESR studies of three regioisomers of the MeS-C{sub 70}{center_dot} adduct formed by photolysis. A 1:3:3:1 splitting pattern was observed for each regioisomer. A methoxy adduct of C{sub 70} was formed by photolysis of di-tert butyl peroxide in the presence of C{sub 70}, but the ESR spectra were too complicated for interpretation. Photolysis of MeOSSOMe generates an MeO{center_dot} radical which adds to C{sub 60} forming MeO-C{sub 60}{center_dot} which was studied by ESR spectrometry. 11 refs., 3 figs., 1 tab.

Iron chelates derived from ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA), ethylenediaminedi(o-hydroxy-p-methylphenylacetic) acid (EDDHMA), ethylenediaminedi(2-hydroxy-5-sulfophenylacetic) acid (EDDHSA), and ethylenediaminedi(5-carboxy-2-hydroxyphenylacetic) acid (EDDCHA) are remarkably efficient in correcting iron chlorosis in plants growing in alkaline soils. This work reports the determination of impurities in commercial, samples of fertilizers containing EDDHMA/Fe3+, EDDHSA/Fe3+, and EDDCHA/Fe3+, The active components (EDDHMA/Fe3+, EDDHSA/Fe3+, and EDDCHA/Fe3+,) were separated easily from other compounds present in the fertilizers by HPLC. Comparison of the retention times and the UV-visible spectra of the peaks obtained from commercial EDDHSA/Fe3+ and EDDCHA/Fe3+ samples with those of standard solutions showed that unreacted starting materials (p-hydroxybenzenesulfonic acid and p-hydroxybenzoic acid, respectively) were always present in the commercial products. 1D and 2D NMR experiments showed that commercial fertilizers based on EDDHMA/Fe3+ contained impurities having structures tentatively assigned to iron chelates of two isomers of EDDHMA. These findings suggest that current production processes of iron chelates used in agriculture need to be improved.

In this paper chemometrics (ANOVA and PCR) is used to measure unbiased correlations between NMR spin-echo decays of pork M. Longissimus dorsi obtained through Carr–Purcell–Meiboom–Gill (CPMG) experiments at low frequency (20 MHz) and the values of 14 technological parameters commonly used to assess pork meat quality. On the basis of the ANOVA results, it is also found that the CPMG decays of meat cannot be best interpreted with a “discrete” model (i.e., by expanding the decays in a series of a discrete number of exponential components, each with a different transverse relaxation time), but rather with a “continuous” model, by which a continuous distribution of T 2 's is allowed. The latter model also agrees with literature histological results.

Biological systems often display multiexponential transverse relaxation times, diagnostic of the presence of different proton pools within the sample. A reliable representation of sample multiexponentiality can be calculated through the inversion of CPMG magnetization decays via the UPEN protocol. However, if a sample contains both liquid- and solid-like protons (as for example in muscle tissue or protein gels) CPMG cannot be used, as the solid-like signal may decay before the first echo is recorded. In these cases signal quantification is more simply attempted in the time domain, by fitting the FID to a discrete number of suitable decaying functions, provided no frequency difference exists between the signal pools. Low field spectrometers (0.47 T or less) are useful in this respect because FIDs obtained at low resolution do not usually carry frequency information. On the other side, they may suffer from very poor magnetic field homogeneity, owing to the fact that they are typically built around a permanent magnet with no shimming facilities, thus producing highly distorted FIDs whose shape can be hardly approximated by meaningful fitting functions. In this work we show that a technique known under the name of reference deconvolution in high resolution NMR can be slightly modified and used successfully in low resolution NMR for fitting highly distorted FIDs.

Photolysis of alkylthiols (RSH) in EtOH/EtOK in the presence of ButOOBut yields the disulfide radical anions RSSR˙– in conditions suitable for EPR detection in solution over a wide temperature range.

The photochemical reaction of the only isolable aromatic thioaldehyde ArCHS (1; Ar = 2,4,6-tri-tert-butylphenyl) in alkaline medium yields ArCH2CH2Ar (2), ArCH2SCH2Ar (3), 6,8-di-tert-butyl-3,4-dihydro-4,4-dimethyl-1H-2-benzothiine (4) and ArMe (5). A radical mechanism which accounts for the formation of these compounds is proposed, mainly on the basis of the direct observation (EPR spectroscopy) of a number of radicals such as ArCHS˙–(A), ArCHCH2Ar (B), and ArCH2˙(D). Results of scrambling of deuterium atoms confirmed the structure of these radicals through interpretation of the corresponding EPR spectra.

On mesure par des techniques de photolyse eclair laser les constantes de vitesse absolue des reactions de radicaux t-butoxyles avec des aldehydes organiques. Parametres d'Arrhenius. Les effets polaires sont tres importants pour determiner la reactivite des aldehydes vis-a-vis des radicaux t-butoxyles

Methanethiyl radicals (CH3S.) are shown to react with cyclic ethers containing double bonds to give addition and hydrogen abstraction from the allylic positions. The esr spectra of the corresponding radicals have been determined. In some cases radicals arising from a rearrangement (probably 1,4 H-shift) were observed. t-Butoxyl radicals also give abstraction and addition with the same substrates. In two cases the barriers to ring inversion for six-membered ring radicals have been determined.

The relative conformer stability in a series of naphthoyl σ-radicals has been investigated by e.s.r. techniques over a wide temperature range. In the case of the 1-naphthoyl radical two rotamers, with a conformational ratio apparently different from that of the parent molecule, were detected. In contrast, in the 2-naphthoyl radical the relative amounts of the conformers are, most likely, dependent upon those in the precursor aldehyde. Structural assignments were achieved by comparing the experimental data with INDO h.f.s. constants. The steric effect on the ratio of the conformers caused by methyl substituents was also examined in order to ascertain the reliability of the INDO approximation.

Addition of trimethylsilyl (Me3Si·) and methylthiyl (MeS·) radical to Me3SiCH2–CHCH2 and MeSCH2–CHCH2 yields, respectively, the radicals Me3SiCH2ĊHCH2SiMe3(I) and MeSCH2ĊHCH2SMe (II) which were observed by e.s.r. spectroscopy. Restricted rotation about the ·CH–CH2 bonds was detected below –100 °C and the free energy of activation determined [3.4 for (I) and 2.85 kcal mol–1 for (II), respectively]. The features of the line shapes also showed that the conformation of (I) is symmetric whereas that of (II) is asymmetric. The geometry of these conformations was also assessed and the angle ϕ between the 2pz orbital of ·CH and the C–X bond was found to be 4–5°§ when X = SiMe3(I) and 10–11° when X = MeS (II). The dependence of the β-splitting on the conformation and on the electronic properties of silicon and sulphur was studied by INDO calculations and the hypothesis that sulphur-containing radicals must be distorted to account for their low aHβ splitting is challenged.

The 9-phenyl thiaxanthyl radical has been obtained from the corresponding cation. A complete analysis of its E.S.R. spectrum has been achieved by using some deuterated derivatives as well as computer simulated spectra. The unusual ratio of the ortho/para hyperfine splittings (✠) has been interpreted as due to the occurrence of restricted rotation of the phenyl ring. Molecular orbital calculations indicate that the experimental results may be interpreted by assuming the phenyl ring to be twisted from the heterocyclic plane by an angle of about 72°. No significant differences were observed between the values of the spin density distribution calculated with standard p and d models.