Solution properties of poly(dialkyl-cyclohexyl) itaconates

Di(methyl-), di(ethyl-) and di(propylcyclohexyl) esters of itaconic acid were polymerized radically in bulk. The products were characterized in solution, then fractionated and the limiting viscosity number/molecular weight relations established for toluene at 25°. From extrapolations to θ-conditions, a set of σ-values from 2.75 to about 2.90 was obtained and compared with published results for poly(dicyclohexyl itaconate) [1], the first member of this polymer homologous series. The non-uniform change of unperturbed dimensions and other thermodynamic parameters are discussed in terms of chemical composition and constitution of the monomer residues.     

High-resolution IR spectrum of fluoroform: a close resonance

A very close triple resonance is observed in the Q-branch region of the C-H stretching fundamental transition in CF₃H. The vibrational perturbations are analysed in terms of the rotational structure and of the vibrational zero-order spectrum of totally symmetric states. The relationship to time-dependent intramolecular processes is discussed.     

Vicinal phenyl group shift in the lead tetraacetate and related oxidations of 5,5,5-triphenyl-1-pentanol

In the lead tetraacetate and heavy metal-bromine oxidations of 5,5,5-triphenyl-1-pentanol 1d, the major cyclization product obtained was the rearranged 2,2,3-triphenyltetrahydro-2H-pyran 11d, resulting from homolytic and heterolytic 1,2-phenyl group shift (the latter only in the lead tetraacetate reaction) in the respective intermediate species with electron deficient δ-carbon 4d and 6d.     

A convenient synthesis of 1α- and 1β-hydroxycholesterol

An efficient procedure for the preparation of 1α-hydroxycholesterol 3-acetate 4 is described, which starts from cholesterol and involves as key steps transannular cyclization of the ten-membered ring ontaining (E)-3β-acetoxy-5,10-seco-1(10)-cholesten-5-one 1 to the oxetane derivative 1α,5-epoxy-5α-cholestan-3β-ol acetate 3, and opening of the four-membered ether ring in the latter compound. 1β-Hydroxycholesterol diacetate 9 was obtained by oxidation of 4 to the 1-oxo derivative 8, followed by metal hydride reduction and acetylation.     

Stereochemistry of cyclic ether formation—II : Intramolecular cyclisation of secondary aliphatic alcohols to tetrahydrofuran-type ethers

The mechanism and stereochemistry of δ-C atom functionalisation in the reactions of secondary straight-chain aliphatic alcohols with lead tetraacetate, ceric ammonium nitrate, and heavy metal (Pb⁴⁺, Hg²⁺, Ag⁺) salts (AcO)^?1, O^2?, CO₃^2?-halogen (I₂, Br₂, Cl₂) combinations are discussed. By demonstrating the intermediacy of 5-bromo-2-hexanol, it was confirmed that the dark silver oxidebromine induced cyclisation of 2-hexanol (and alcohols in general) involves (as the other hypohalite reactions) intramolecular 1,5-hydrogen abstraction by alkoxy radicals and formation of δ-bromohydrins. A novel and simple procedure for obtaining tetrahydrofurans from alcohols by way of the hypochlorite reaction, using silver or mercuric salts and chlorine, is described.     

Circular dichroism of some cyclopropane ring containing 1,3-cyclo-5,10-seco-steroidal ketones

Circular dichroism of the rearranged keto steroids 3 and 4, containing a condensed three and nine-membered ring system, shows that the conformation of the nine-membered ring is the same in solution as in the crystal; reduction of the kto group does not change this situation. CD also indicates that epimerization at C(5) in the pair $\text{7}\text{8}$ and the pair $\text{11}\text{12}$ leaves the cyclononanone ring conformation unchanged.     

Structure-reactivity relationship in the solvolysis of 5,10-secosteroidal 5-p-nitrobenzoates1

The solvolysis of (Z)- and (E)-3β-acyloxy-5,10-seco-1(10)-cholesten-5β-ol p-nitrobenzoates 4 and 5 has been investigated and compared with the solvolytic reactivity of the epimeric (Z)- and (E)-5α-p-nitrobenzoates 1 and 2, as well as of the reference compound, i.e. the 1,10-saturated 5α-p-nitrobenzoate. Kinetic data and product analysis revealed that the relative spatial orientation of the 1(10)-olefinic double bond and the chiral center at C(5) in the 10-membered ring, which these secosteroidal 5-p-nitrobenzoates can adopt in the transition state, is the main factor which determines their solvolytic behaviour, so that the esters 1,2 and 5 solvolyse with transannular double bond participation, while such an interaction is not present in the case of the (Z)-5β-ester 4.     

Synthesis,structure and reactions of seco-steroids containing a medium-sized ring—IX : Reactions of Δ1(10)-unsaturated 5-oxo-5,10-seco-steroids with hydroxylamine and n-methylhydroxylamine

When treated with hydroxylamine or N-methylhydroxylamine, in the presence of proton donor catalysts, trans-Δ¹⁽¹⁰⁾-unsaturated 5-oxo-5,10-seco-steroids, such as 3 (but not the corresponding diastereomeric cis-compounds), are converted stereospecifically and in good yield to isoxazolidine derivatives (e.g. 4 and 13), resulting from transannular 1,3-dipolar addition of the intermediately formed oximes and nitrones to the trans-double bond in the cyclodecene ring moiety of the seco-steroid system. Reactions are described and physical evidence is presented which establish the constitution and configuration of the isoxazolidine-containing cycloaddition products, and the mechanistic and steric course of this transannular ring closure process is discussed.     

Dielectric properties of poly(4-methylphenylisocyanate) and poly(4-methoxyphenylisocyanate) in solution

In the range 200 Hz-2 MHz, the dielectric behaviour of two polyarylisocyanates depends on the solvent. In certain solvents, such as toluene, there is only one high frequency absorption for poly(4-methylphenylisocyanate) and it is independent of molecular weight. Its character corresponds to chains having a low kinetic flexibility. In other solvents, this polymer, as well as poly(4-methoxyphenylisocyanate), shows two regions of dielectric absorption. The low frequency relaxation is molecular weight dependent: a polarization due to solvent polymer interactions occurs along the main chain. Despite its solvent-dependence, the total dipole moment of these polyarylisocyanates which behave like coils is much lower than that of polyalkylisocyanates, which are known to be rod-like.     

A study of lanthanide p-toluene sulphonic acid complexes in solution

Lanthanide p-toluene sulphonic acid (ptsa) complexes were prepared for La, Pr, Nd, Sm, Eu, Dy, Ho, Er and Yb, and found to exist as Ln(ptsa)₃. Conductivity studies of La(ptsa)₃ in DMSO and DMF suggest 1:2 and, possibly, 1:1 electrolyte behaviour in these solvents, respectively. NMR lanthanide-induced chemical shifts (LIS) for aromatic protons in (ptsa)^? and methyl protons in DMSO, were measured for all complexes as a function of the [Ln³⁺[DMSO] in a medium consisting of CCl₄, DMSO, and CH₃CN. Analysis of the LIS data suggests a change in (ptsa)^? coordination round Ln₃₊ across the lanthanide series.     

Synthesis and solution properties of comblike poly(mono-n-alkyl itaconates). I. Poly(monodecyl itaconate)

The monoester of itaconic acid with n-decyl alcohol was prepared and polymerized. The polymer was fractionated and characterized by viscometry, size-exclusion chromatography (SEC) and light scattering. Some of the common semiempirical relations for flexible and rigid polymers were used in order to obtain the unperturbed dimensions and the conformational parameters. Thermodynamic and dimensional parameters were determined and calculated. The results are compared with those reported previously for similar compounds.     

Non-aqueous redox determination of ascorbic acid with copper (II)

Hydrated copper (II) perchlorate (in acetonitrile) has been used for the direct visual and potentiometric determination of ascorbic acid in acetic acid-acetonitrile media. Diphenylamine and diphenylbenzidine are suitable indicators. A bright platinum wire is used as indicator electrode and a modified calomel or an antimony electrode as reference electrode for the potentiometric titration. Ascorbic acid is oxidized to dehydroascorbic acid. The proposed method is simple, accurate and reliable. The reverse titration also works well.     

Synthesis and solution properties of poly(2-methylproline)

The resolution of 2-methylproline and the assignment of absolute configuration to the stereoisomer has been carried out. The L-enantiomer was obtained from the fractional crystallization of the quinine salt of (?)-N-carbobenzoxy-2-methylproline and the D-enantiomer from the collected filtrates. The (?)-2-methylproline was assigned the L-configuration by means of the Clough-Lutz-Jirgensons method. Polymers were obtained in bulk from the N-carboxyanhydrides. Although polymers obtained from different solvents exhibited different solubility properties, subsequent spectral studies indicated that this effect was not due to a large conformational change as in the polyproline case. Spectral evidence suggests that poly(2-methylproline) (P2MP) exists as a polyproline type II helix.     

Synthesis and solution properties of poly(ditoluyl itaconates)

The three o-, m- and p- isomers of ditoluyl itaconate were obtained by esterification of cresols and itaconic acid in the presence of diphosphorous pentoxide, and then polymerized in bulk with AlBN as initiator. The polymers were investigated in dilute solution, including $\text{M}{}_{\mathrm{W}}$ determination and precipitation fractionations, and the results compared with those for poly(diphenyl itaconate). The presence and position of -CH, in the aromatic ring influence the initial rates of polymerization, polymer solubilities in organic solvents and $\text{[η]/}\text{M}{}_{\mathrm{W}}$ relations. Unperturbed dimensions, obtained by extrapolating to τ-conditions, vary slightly with the -CH, group position, due to steric and probably other effects.     

Mass spectrometric evolved gas analysis (MSEGA) study of the thermal decomposition of poly(1,2-acenaphthenediylidene) and poly(1,2-acenaphthylenylene) in vacuo

A mass spectrometric study of the thermal decompositions in vacuo of two polyene polymers, poly(1,2-acenaphthenediylidene)-I and poly(1,2-acenaphthylenylene)-II, was performed in order to establish the differences between their structures. Evolution of repeating units from a chain depropagation process of both polymers was observed. Annealing of the polymers prior to decomposition changed the temperature at which maxima were observed on the MSEGA ion current temperature profiles. These profiles of both polymers after annealing became more similar in shape and temperature location. These changes in MSEGA behaviour as a result of annealing can be attributed to an equalisation of the single and double bonds in the structure of the polymers. The kinetic study of the thermal decomposition of non-annealed polymers showed that the decomposition reaction for polymer I is isokinetic, i.e. of the same kinetic mechanism, when the fraction of sample decomposed “α” is in the range 0.4–0.7 with values of 127.8 ± 3.6 kJ mol^?1 for the activation energy and 2.6 ± 2.2 × l0⁷ s^?1 for the A factor. Polymer II did not show clearcut isokinetic behaviour, the activation energy increasing from 99.4 kJ mol^?1 at α = 0.4–113.5 kJ mol^?1 at α = 0.7. This change is attributed to the structure of the polymer altering during the course of the decomposition. The differences in the thermal properties lead to the conclusion that there is a bond alternation in the polyene chains of both polymers.     

Isotopic effects of carbon and nitrogen in low-temperature photochemical reactions

Isotopic effects of carbon and nitrogen in the low-temperature photodecomposition of benzoyl peroxide and diazoaminobenzene have been observed and discussed in terms of preferential electronic energy transfer to species containing lighter isotopes.     

Resolution enhancement of a.c. polarographic peaks by deconvolution using the fast fourier transform

A method for resolution enhancement of a.c. polarograms (voltammograms) is presented. The method is based on deconvolution using fast Fourier transforms. Overlapped a.c. polarograms are mathematically narrowed and sharpened, retaining the peak position and linear proportionality of the sharpened peak height with concentration. The advantages and limitations of the method are demonstrated on simulated and experimental a.c. polarograms. The same approach is applicable to related techniques such as. differential pulse and square-wave polarography.     

Synthesis and properties of alkyldicyclopentadienyl-vanadium(III) compounds

The compounds Cp₂VR (R = CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁, CH₂C(CH₃)₃ or CH₂Si(CH₃)₃) have been prepared from Cp₂ VCl and RMgX in n-pentane. The air-sensitive compounds are stable at room temperature, but decompose between 65 and 138°C. The thermal stability decreases in the order R = CH₃ CH₂Si(CH₃)₃ > C₂H₅ > CH₂C(CH₃)₃ > n-C₅H₁₁ > n-C₄H₉ > n-C₃H₇. Compounds with R = i-C₃H₇ or t-C₄H₉ could not be obtained.     

Kinetics of thermal dehydration of some bis-(4-aminosalicylato)-diaquo complexes of transition metal ions

The kinetics of thermal dehydration of bis-(4-aminosalicylato)-diaquo complexes of VO(II), Cu(II), Ni(II), Co(II), Fe(II) and Mn(II), were studied. The activation energies and other kinetic parameters have been evaluated. The observed kinetic parameters indicate a first-order reaction. The activation energy of the thermal dehydration decreases in the order: VO(II) > Cu(II) > Co(II) > Ni(II) > Fe(II) > Mn(II), which is also the order for the covalency in the MO bonds.