Carbon-13 chemical shifts of 3-substituted thietanes,thietane 1-oxides and thietane 1,1-dioxides

Carbon-13 chemical shifts of the α- and β-carbon atoms for 12 thietane 1,1-dixides, 9 thietane 1-oxides and 7 thietanes with a variety of 3-substituents [H, CH(CO₂Et)₂, SEt, Br, SPh, Ph, Cl, NMe₂, OH, OSiMe₃, OAc, OEt] are correlated according to the nature of the sulfur atom (Y=sulfone, sulfoxide, sulfide) and the nature of the 3-substituent (X) by the equations δ_α= a_Y+b_X and δ_β=a_X+b_Y, where a and b are parameters characteristic of X and Y. One-bond coupling constants [J(CH)] are reported for 21 compounds. The chemical shifts for the α- and the β-carbon atoms of the sulfones show the ‘fore-membered ring sulfone effect’ (α-carbon unusually deshielded, β-carbon unusually shielded), but the α-carbon-hydrogen coupling constants are similar to those of the sulfoxides and sulfides; the β-carbon-hydrogen coupling constants are sensitive to the nature of the substituent (X) but no special β-effect is observed. Comparison of the chemical shifts of the α-methylene carbon atoms of 3-phenyl-, 3-(β-naphthyl)- and 3-(α-thienyl)-thietes with those of the coresponding sulfones also reveals the ‘four-membered ring sulfone effect’ cis- and trans-3-Substituted thietane 1-oxides may be distinguished by the greater downfield shift for the β-carbon atom in the trans-isomer.     

Carbon-13 n.m.r. spectra of branched carboxylic acids and their derivatives

¹³C n.m.r. spectra have been measured for 39 compounds with branched structures including carboxylic acids, their methyl and ethyl esters, nitriles and chlorinated esters. The results obtained indicate that the ¹³ C n.m.r. technique is applicable to structure assignment of acids and their derivatives containing various numbers of substituents on the chain. The dependence of the carboxylic carbon chemical shift on the number and structure of α-positioned substituents has been determined. Calculation of the chemical shifts for branched carboxylic acids, esters and nitriles from the corresponding increments using the additivity scheme is shown to be possible in principle.     

Effect of the structure of alkoxy radicals on the mass-spectral fragmentation of dialkyl alkylphosphonates

Basic fragmentation reaction of dialkyl alkylphosphinates under the conditions of electron ionization proceeds in two steps. In the first step occurs cleavage of C-O bond and splitting the olefin radical off. The intermediate ion formed therewith exerts further fragmentation by the similar way. Peaks of the intermediate ions occurs in the spectra of all dialkyl alkylphosphonates except O-methyl derivatives. In the case of branching at α-carbon atoms of alkoxy radicals cleavage of the first carbon-carbon bond of the alkoxy radical unlike the case of alkyl fluorophosphonates, in the intermediate ion rather than in molecular ion and accompanied by the elimination of alkane. These found regularities allow to explain principal fragmentation pathways of a wide series of phosphoric acids esters of general formula (RO) _n P(O)X _n?3 (where X is R, Hal, or OMe) with both linear and branched in α-position alkoxy radicals.     

Etude par Résonance Magnétique Nucléaire du carbone 13 de complexes du cobalt (III) et de la diméthylglyoxime

From a carbon magnetic resonance study of several alkylcobaloximes RCo(DMG)₂B (DMG = dimethylglyoximate monoanion), it was possible to estimate the α, β and γ effects of the Co(DMG)₂B group on the chemical shifts of the carbon atoms of various alkyl groups R. The chemical shifts of the carbon atoms belonging to the equatorial ligands and to the axial base B are not significantly affected by structural modification of the R groups. Values of δ in benzylcobaloximes XC₆H₄CH₂Co(DMG)₂B agree with a donor effect of the ? CH₂Co(DMG)₂B radical. Values of ¹J(¹³C? H) coupling constants, measured in ¹³C enriched methylcobaloximes, do not vary appreciably when B is changed (J(¹³C? H) = 137 ± 1 Hz) and are close to the value obtained for methylcobalamine.     

The temperature dependence of 13C NMR shifts in polar compounds and its role for the determination of conformational equilibria

Intrinsic temperature dependencies of ¹³C NMR shifts in alkanes bearing one polar C-α? X bond are determined with neopentyl and 4-tert-butylcyclohexyl derivatives as conformationally homogeneous model compounds. The increased shiedling for C-α at higher temperatures can be related to a C-α—X bond length increase and, for less polarizable C? X bonds, essentially to a decrease of solvent polarity on raising the temperature. The use of temperature dependent ¹³C shifts in conformationally mixed compounds for the determination of the equilibrium constants, K, is evaluated with n-propyl halides; the computer fit of the unknown conformer shifts and the conformational enthalphy difference, δH° to the time averaged shifts yields δH° values which, although converging rather broadly, are in general agreement with literature data. In compounds with higher conformational barriers, such as methoxy- and bromocyclohexane, low temperature signal integration yields accurate δG° values; inclusion of shifts above coalescence, however, yields unreliable δH° and δS° parameters. This can only partially be remedied by application of temperature shift corrections obtained from parent t-butylcyclohexyl compounds.     

Study on 15N NMR of lithium sudan I complex

The ¹⁵N chemical shift have been measured for α-¹⁵N-labelled phenylazo-2-naphthol and its lithium complex. The change of the ¹⁵N chemical shift on coordination of the azo nitrogen to lithium appears to be related to those of protonation of the same nitrogen. The chemical shifts of azo form and hydrazone form have been calculated according to the weighted δ_N and ¹J_NH of different fractions. It is concluded that there is a bond formation between Li and N atoms.     

Hydrocarbomethoxylation of C5-C9 olefins with formic acid and methanol under conditions of catalysis with phosphoric acid

Conclusions The methyl esters of branched carboxylic acids containing quaternary and tertiary C atoms in the-position, together with a small amount of the corresponding carboxylic acids, are formed during the hydrocarbomethoxylation of the straight-chain C₅-C₉ olefins at atmospheric pressure in the presence of concentrated H₃PO₄.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 454–456, February, 1973.     

Study of the uptake of inorganic ions and organic acids at theα-alumina-electrolyte interface in a colloidal system by radiochemical techniques and microelectrophoresis

The interactions of the alumina-electrolyte in the presence of inorganic ions (copper, selenium) and/or organic acids (benzoic acid, glutamic acid, phenol) have been studied. The acid-based properties of-alumina have been determined in NaCl media (pzc=8.5±0.3). Three types of hydroxy groups with different acidity constants have been found. The adsorption of copper and selenium have been described by the formation of the surface complexes: (=Al¹–OH, CuCl) and (=Al¹, SeO₃)^–. The interaction of copper with the surface oxygen atoms is strong and so is the interaction of selenium with the surface aluminium atoms, which involves a shift of the iep of alumina. For the three organic acids studied (HX), the adsorption equilibrium is:=Alⁱ–OH+HX(=Alⁱ, X)+H₂O. The interaction of the X^– group and the aluminium atoms is strong following the order: glutamic acid > benzoic acid > phenol. The uptake of selenium is uninfluenced by the presence of organic acids with carboxylic, amino-acidic and phenolic groups. The uptake of copper is highly increased by the presence of organic acids but it is not influenced by the presence of the phenolic groups. Both of these behaviours can be extrapolated to inorganic ions of the same chemical structure.     

Carbon-13 NMR studies of 1-aryl-3-phenyl-2-thioxo-4-imidazolidinones. Conformational isomerism and substituent effects

Characteristic ^13C chemical shift ranges and substituent shifts of heterocyclic ring carbon atoms have been identified for a number of 1-aryl-3-phenyl-2-thioxo-4-imidazolidinones. ¹³CNMR spectra may be used to detect slow internal rotation about the aryl C? N-1 bond in compounds with diastereomeric rotational isomers; many corresponding carbon atoms in the rotamers have distinctly different chemical shifts. The δ-effects originating from aryl ortho substituents are both electronic and steric in origin.     

Free radical addition of F-alkyl compounds to unsaturated carboxylic anhydrides and their derivatives

Many perfluoroalkyl-substituted organic compounds have been obtained through free radical addition of F-alkyl iodides to a center of unsaturation:

X, Y, and Z may include carbon chains, rings and various substituents. During the course of these synthetic studies—done over a span of several years—significant discoveries in mechanism and structure have been made.Today I wish to report some free radical additions of F-alkyl iodides to unsaturated anhydrides and their derivatives. Among the compounds recently discovered are the norbornene products 5 to 10.

Spectroscopic properties of the adducts varied with position and nature of the substituents. Somewhat surprisingly, the chemical shift of protons on the R_F side of the molecule was affected by changes in substituents on the other side of the molecule.Various reactions of the adducts were studied. Unusual stereospecificity in lactone formation and in base- induced cyclization to nortricyclene derivatives was observed. Only when the iodo group was in an endo position did these reactions occur.Analogous free radical addition of fluorinated thiols (R_FCH₂CH₂SH) to norbornene anhydrides produced a series of 5-polyfluoroalkylthionorbornane-2,3-dicarboxylic acid anhydrides(11, 12; U S Patent 3,989,725 (1976). As in previous studies the entering group took up the exo position exclusively. Reaction with acids, esters or norbornene carboxylic imides of the fluorinated thiol also gave analogous products.Because of the hydrophobic nature of the F-alkyl groups the entire range of compounds displayed pronounced surface-activity and would appear to have utility in a wide range of applications.

     

Carbon-13 NMR spectra of DDT,its analogues and related compounds

Carbon-13 NMR spectra of mono- and disubstituted aromatic compounds including DDT, its analogues, homologues, derivatives and certain model compounds have been studied. The Savitsky scheme of carbon chemical shifts in disubstituted benzenes is applicable to these compounds. The data obtained show that in mono- and disubstituted aromatic compounds containing two different substituents in the α- and β-positions of the side chain, the substituted ring carbon atom shifts follow the additivity rule and can be calculated from substituent increments. Mutual effects of substituents in the ring and in the side chains are analysed. The chlorine atoms in α-position to the phenyl ring give rise to an additive α-effect of about 25 ppm, as in perchloroalkanes. The influence of a β-chlorine atom in the side chain on the substituted carbon atom in the ring is, however, only 3 ppm as against the usual value of about 10 ppm for the β-effect in alkyl chains. Moreover, the first β-chlorine substituent has no noticeable influence on the substituted ring carbon chemical shift: the effect of 3 ppm is transferred to the para-carbon atom almost without attenuation. The ring substituted carbon atom signal shifts caused by the γ-effect of chlorine in the side chain are similar to those observed in aliphatic chains. The ortho-chlorine substituents shift the side chain α-carbon atom signal by 3.6-5.2 ppm to high field compared to para-chlorophenyl compounds. This is similar to the chlorine γ-effect in aliphatic chains.     

15N NMR studies of amino acids and their reaction products with formaldehyde

Natural abundance ¹⁵N NMR spectroscopy has been used to investigate the effect of pH on the ¹⁵N chemical shifts of lysine and of ε-hydroxymethyllysine. A computer calcualtion which fits the chemical shifts of both α-and ε-nitrogen atoms versus pH has been used to predict the pK_a values. ¹⁵N chemical shifts and some ¹J(¹⁵NH) values of some other amino acids and of their reaction products with formaldehyde are also reported.     

Effets stériques des groupes alkyle sur le déplacement chimique des hydrogènes d'un méthyle: Correlation avec les termes Es de Taft

The effect of alkyl groups (Me, Et, i-Pr, t-Bu) on the ortho methyl proton chemical shifts is shown to be linearly correlated with the Taft (E_s) scale in model compounds 1 . Experimental results can be expressed by Δδ = δ_R – δ_Me = λ′E_s in which λ′ is solvent and model dependent. The calculations of the chemical shifts according to ApSimon and Buckingham are used to show the predominant influence of steric effects on the observed substituent effect.     

Fourier-transform infrared studies of polypropylene during mechanical deformation

Quantitative Fourier-transform infrared (FTIR) measurements of frequency shifts Δν and absorbance profile asymmetry are reported for various polypropylene samples as a function of uniaxial stress σ. Generally, it was found that the frequency shift coefficient α_χ, defined by Δν = α_χσ, depended on stress rate \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, draw ratio, λ, molecular orientation f, tensile modulus E, and annealing conditions. With annealing, α_χ decreased with increasing shrinkage in the case of highly oriented isotactic PP. The α_χ values for the “helix bands” were less affected than those for the “liquid bands.” With increasing \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, generally α_χ increased to an apparent asymptotic limit. With increasing λ, f, or E, α_χ also increased from α_χ ? 0 for λ = 1 (spherulitic) to maximum values for highly oriented isotactic PP. The observed variations in α_χ can be interpreted in terms of the changes in the peak position and shape of the nonuniform molecular stress distribution. Analogous behavior with x-ray diffraction peaks obtained for polymers under stress is discussed.     

Correlation of activation energies of radical–molecule metathesis reactions with enthalpic,polar, and steric parameters

It is shown that the activation energies E oF chlorine atom abstraction by cyclohexyl radicals and hydrogen atom abstraction by Cl atoms from polychloroalkanes can be correlated with the bond dissociation energies D and the Taft polar and steric substituent constants σ* and E_s by the expression: where ΔE and ΔD represent the differences between the E and D values of a given substrate and those of a reference compound (CH₃ substituted substrate) and α, ρ, and δ are the corresponding correlation coefficients. The use of this expression allows quantitative evaluation of the relative contribution of the various factors affecting the activation energies of these reactions and estimation of related thermochemical data.     

A novel one-pot synthesis of α-keto-1,3,4-oxadiazole derivatives based on isocyanide-Nef reaction

Various α-keto-1,3,4-oxadiazole derivatives were synthesized through a sequential intermolecular dehydrochlorination/intramolecular aza-Wittig reaction of carboxylic acids and imidoyl chloride intermediates, which were generated by isocyanide-Nef reaction of acyl chlorides and (N-isocyanimine) triphenylphosphorane (1) in CH₂Cl₂ at room temperature.     

13C chemical shift subsitituent parameters for alkyllithium compounds in hydrocarbon solvents

¹³C chemical shift substituent parameters are presented for carbons α, β, γ, and δ to the lithium atom based on the chemical shifts of 14 ⁶Li-enriched alkyllithium compounds. The chemical shift of the carbon α to lithium depends on the branching of alkyl group at the α-carbon and on the aggregation state of the alkyllithium compound. Increased branching results in increased upfield shifts. This is interpreted in terms of the varying electronic nature of the alkyllithium compounds. The chemical shift of the carbon β to lithium substitution is shifted downfield approximately 5 ppm from the corresponding carbon in the parent hydrocarbon, irregardless of the alkyl group or the aggregation state of the alkyllithium compound. The chemical shift of the γ-carbon depends on the steric requirements of the alkyl group. Carbons four or more bonds from lithium have the same chemical shift as those of the parent hydrocarbon. The derived chemical shift parameters are used to assign the α-carbons of two alkyllithium compounds formed from the reaction of t-butyllithium and trimethylvinylsilane.     

A new cataluminescence sensor for carbon tetrachloride using its catalytic reduction by hydrogen on palladium/carbon surface

A new cataluminescence (CTL) sensor was developed based on the chemiluminescence (CL) emission from the catalytic hydrodechlorination of carbon tetrachloride on the surface of palladium/carbon catalyst. The factors influencing the CTL signal, such as the catalyst, carrier gas, gas flow rate, temperature and the CL wavelength, were investigated in detail. Under the optimal conditions, the linear range of the CTL intensity versus concentration of carbon tetrachloride was 4.7–235 μg/mL (R = 0.9944, n = 7), with a limit of detection of 0.7 μg/mL (σ = 3). GC/MS results suggest that the possible CTL mechanism of the reduction is the formation of CCl₃ radicals. The CCl₃ radicals combine with H free atoms or capture hydrogen atoms from H₂ molecules to form excited CHCl₃ intermediates, which decay from the excited-state to the ground giving CTL emission for the detection. It is also found that some benzene derivatives with α-H of branched-chain, such as toluene, ethylbenzene and xylenecan, can play a role of catalyst in the reaction.     

Bond dissociation energies and the Hammett correlation,Part 1: Remotely substituted aromatic compounds and vitamin E

Four hundred and seventy nine experimental values of X? Z bond dissociation energies (BDEs) of para‐, ortho‐, meta‐, and multisubstituted aromatic compounds were reproduced by the following simple equations: Here X represents a wide variety of univalent atoms or groups; Y is one or several various remote substituents; and Z represents an oxygen, nitrogen, carbon, or sulfur atom. DH⁰(X? ZC₅H₆) is a known reference/anchor point for a series of X? Z bonds. E_sr is the remote conjugation energy between the substituents and the reaction center (broken bond), and can be expressed as a Hammett‐type correlation. σ⁺(Y) is the Brown–Okamoto constant of a substituent Y or the sum of several substituent constants. The Hammett slope or reaction constant ρ is a linear function of the difference between the covalent potentials V_x(Z) and V_x(X). It has been found that and The set of equations are very powerful for the prediction of BDEs, chemical reactivity, and reaction center (or active site) in antioxidants, nutrients, pharmaceuticals, toxicants, carcinogens, and explosives. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 453–466, 2002     

An NMR study of 2-alkoxy-1,3,2-dioxaphospholanes. I—13C chemical shifts

Measurements of the ¹³C chemical shifts of 2-alkoxy-1,3,2-dioxaphospholanes have allowed the determination of the contribution of the substituent to the α-, β- and γ-carbon chemical shifts of attached alkyl groups. The preliminary assignments of the signals were made using the following information; relative intensities, variations in coupling constants J(³¹P¹³C) and the existence of linear correlations between the shifts of carbon atoms in the P-alkoxy groups and the degree of substitution of the observed carbon or of its neighbours.