Cross-conjugated biradicals: Kinetics and kinetic isotope effects in the thermal isomerizations of cis- and trans-2,3-dimethylemethylnecyclopropane,cis- and trans-3,4-dimethyl-1,2-dimethylenecyclobutane,and of 1,2,8,9-decatetraene

cis- and trans - 2,3 - Dimethylenemethylenecyclopropane ($\text{C}$ and $\text{T}$) interconvert at 160.0° with a small normal kinetic isotope effect (KIE) when the exo-methylene is deuterated, but the 1,3-shift products, 2-methylethylidenecyclopropane, show a large normal KIE, 1.35 and 1.31, when formed from $\text{C}$ and $\text{T}$, respectively. This data can be interpreted in terms of either parallel reactions or a common trimethylenemethane diradical intermediate formed with a normal KIE of 1.11 and closing to 1,3-shift product with a normal KIE of 1.29 due to the effect of deuterium in the required 90° rotation of the exo-methylene carbon.The kinetics of the thermal 1,3- and 3,3-shifts of cis- and rans-3,4-dimethyl-1,2-dimethylenecyclobutane ($\text{CB}$ and $\text{TB}$) were determined in a flow reactor. The first order rate constants are log k_CB (sec^?1) = 13.7 ? 42,200/2.3 RT and log k_TB (sec^?1) = 13.6 ? 41,900/2.3 RT (E_a in kcal/m) which compare favorably to that from the parent hydrocarbon. 1,2-dimethylenecyclobutane, after reasonable correction for dimethyl substitution.Rearrangement of $\text{TB}$ and its bis(dideuteriomethylene) derivative at 230.0° revealed a normal KIE of 1.08. This KIE could be interpreted in terms of either a methylene rotational isotope effect in a concerted reaction or formation of a bisallyl diradical with the expected normal rotational IE on closure to the 1,3-shift product of 1.12 with no IE in the ring opening when the result is corrected for return of the biradical to starting material.The kinetics of intramolecular 2 + 2 cycloaddition of 1,2,8,9-decatetraene were determined in a flow reactor. The first order rate constant is log k(sec^?1) = 9.4 ? 30,800/2.3 RT (E_a in kcal/m). These energetics are compared with those of other 2 + 2 cycloadditions. The major product is 3,4-dimethylenecyclooctene ($\text{DC}$) which is also found from the minor product, cis-7,8-dimethylenebicvyclo[4.2.0]octane ($\text{CO}$), at higher temperatures. The trans isomer, $\text{TO}$, also gives $\text{DC}$ at about the same rate as $\text{CO}$.     

Gradient expansion of the atomic kinetic energy functional

It is demonstrated that the ground-state atomic kinetic energy functional T[?], where ? is the electron density, can be computed to surprising accuracy from the truncated gradient expansion: T[?] = + T₂[?] + T₄[?], with T_o[?] = $\text{3}\text{10}$(3π²)$\text{2}\text{3}$ ∫ ?$\text{5}\text{3}$ d_τ, T₂ [?] = $\text{1}\text{72}$ ∫ (??)²?^?1 d_τ, and T₄ [?] given by the formula of Hodges. Calculations of T₀, T₂ and T₄ are reported for He with ? both the Hartree—Fock and a very accurate density, and for Ne, Ar and Kr with ? the Hartree—Fock density. For Kr, T₀ + T₂ + T₄ is within 0.3% of the exact Hartree—Fock T, with T₂/T₀ = 0.05, T₄/T₂ = 0.17.     

Dissolution of Ca3(AsO4)2 · 2H2O in the system CaOAs2O5H2O at 35, 40, 45 and 50°C and the related thermodynamic data

Calcium arsenate dihydrate is precipitated at pH 7.0 and its dissolution in aqueous solutions at temperatures of 35, 40, 45 and 50°C and a pH of between 3.0 and 8.0 is investigated. The thermodynamic parameters ΔG⁰, ΔS⁰ and ΔH⁰ for the process are evaluated. Temperature dependence of solubility is obtained by the equations ?log K_TCA = $\text{9078.138}\text{T}$ ? 34.0468 + 0.0821421 T     

2-Formylation of 3-arylindoles

The preparation of $\text{N}$-substituted-3-(4-fluorophenyl)indoles R = H, CH₃, $\text{i}$-Pr) and their direct formylation at the 2-position by Vilsmeier-Haack or Friedel-Crafts methodologies is described.     

Ritter-reaction on steroids: Ring expansion of steroid oxethans into dihydrooxazines

The 3β-acetoxy-16β,17β-epoxymethyleneandrost-5-ene ($\text{1}$) transforms into the dihydrooxazine condensed to the sterane skeleton ($\text{4}$$\text{a}$,$\text{b}$,$\text{c}$,$\text{e}$,$\text{g}$,$\text{i}$) in a ring-expansion reaction with alkyl and aryl nitriles in the presence of HBF₄— diethyletherate The 3β-acetoxy-16α, 17α-epoxymethyleneandrost-5-ene ($\text{9}$) undergoes a Wagner-Meerwein rearrangement under similar conditions.     

Thermal decomposition studies. Part XII. Kinetics of dehydration of calcium oxalate monohydrate. Multiple correlation with heating rate and sample mass

The kinetic parameters (energy of activation, E, and pre-exponential factor, A) from non-isothermal TG data have been correlated, for the first time, with simultaneous variations of both the procedural factors (heating rate and sample mass) by multiple regression analysis. The unique equation based on the mechanism of the reaction as well as three general mechanism-non-invoking integral equations were used to calculate E and A from the TG data for the dehydration of CaC₂O₄ · H₂O. The kinetic parameters calculated using all four equations showed a systematic trend and the results can be expressed as E(or log A) = $\text{constant}\text{heating rate}$ + $\text{constant}\text{mass}$ + constant     

Investigations on the influence of charge density on the mutual deactivation of polyion-macroradicals—II

Bimolecular rate constants (2 k_R) of the reaction R· + R· in aqueous solution were measured using the pulse radiolysis technique. R· designates radicals produced by H atom abstraction from polyvinyl alcohol partially acetalyzed with glyoxylic acid. Due to the expansion of the coils, 2 k_R increases with X_i the content of ionized base units in mole %. Above a critical value x_i (crit), 2 k_R decreases due to intermolecular repulsion. x_i(crit) decreases with increasing chain length $\text{n}{}_{\mathrm{<mtext>n</mtext>}}$ [x_i (crit) ≈ 0·5 mole % at $\text{n}{}_{\mathrm{<mtext>n</mtext>}}\text{= 3000}$ and x_i (crit) ≈ 1·5 mole % at $\text{n}{}_{\mathrm{n}}\text{= 270}$]. In the presence of NaClO₄, the following salt effects were observed: for x_i >x_i (crit), 2 k_R is increased because the intermolecular repulsion is partially depressed by screening. Below x_i (crit), 2 k_R is decreased since the coil expansion is diminished. At very low values of x_i where the coil expansion due to intramolecular repulsion is negligible, no salt effect was detectable.     

On the sign of the dipole moment derivatives in CH3X (X = F, Cl, Br, I)

It is shown in this paper that the principal methods for reducing the indeterminacy of the sign of (δ M/δ$\text{O}$_i) (isotropic invariance of M, quantum mechanical calculations, determination of (δM/δ$\text{O}$_i) via high resolution data or the Stark effect) lead, in the case of CH₃X (X = F, Cl, Br, I) molecules, to contradictory conclusions. The discrepancies are illustrated and discussed. It is also pointed out that either a revision of the previous results or a calculation of electro-optical parameters on a set of chemically similar molecules including CH₃X could possibly lead to a unique determination of the sign.     

Neutron activation analysis of high-purity selenium : Determination of phosphorus,sulfur and chlorine

Chlorine was determined in selenium by irradiation of 2-g samples for 37 min at a flux of 8·10¹⁰ n/cm²/sec. Chlorine was volatilised from hot concentrated nitric acid and precipitated as silver chloride. The isotope ³⁸Cl (T_{$\text{1}\text{2}$}=37.3 min) was counted by γ-spectrometry. Sulfur and phosphorus were determined by irradiating 50-mg samples with and without cadmium shielding for 4 days at a thermal flux of 6·10¹² n/cm²/sec and a fast flux of 4·10¹¹ n/cm²/sec. The matrix activities were separated by distillation from sulfuric acid-hydrobromic acid at 200–220°. The isotope ³²P (T_{$\text{1}\text{2}$}=14.3 d) was then precipitated, together with phosphate carrier, as ammonium phosphomolybdate, and counted with a G.M. tube. Amounts of 0.4–1 p.p.m. chlorine, 65–520 p.p.b. phosphorus and 1.5–4.6 p.p.m. sulfur were found in high-purity selenium samples.     

A method for obtaining potential parameters for helium from T1 measurements

The temperature dependence of T₁ for ³He gas in the range 0–4°K is calculated for a Lennard-Jones (12,6) potential. The relaxation of the nuclear spins is assumed to be due to a dipolar interaction between the nuclei. A minimum value in the relaxation time, T_1,min, is found to occur at a temperature denoted by T_min. By repeating the calculation for different pairs of values of the potential parameters ? and σ, we have found that for a density of 10^?2 g/cm³,σ²T_min = 13.0?1.12 × 10³ ?σ², T_1,min/σ²(T_min)^{$\text{1}\text{2}$} = 17.4?6.56 × 10² ?σ², with ?, σ, T_min and T_1,min in eV, Å, °K and minutes, respectively. From measurements of T_min and T_1,min, ? and σ can be determined.     

Autoxidation of cyclic olefins in perfluorinated organic solvents

It is well known that several perfluorinated organic compounds (particularly alcanes and cyclic ethers perfluor$\text{i}$nated) have specific properties like solvents of biatomic gas and oxygen.Since these perfluorinated compounds have also suff$\text{i}$cient capabilities as solvents of several alifatic hydr$\text{o}$carbons and pratically none as solvents of their oxidation products (alcohols, ketones; peroxides, acids, water, etc.), these solvents seem ideal for the studying of oxidation reactions in liquid phase.The kinetics of autoxidation, with O₂ for temperatures between 15°C and 60°C, of cyclohexene and methyl cyclohexenes, have been studied in fluorinated solvents (various mixtures of 3,n-perfluoro-propyl-perfluoro-tetrahydrofuran, and 3,n-perfluoro-buthyl-perfluoro-tetrahydropyran) with formula C₈F₁₆O. This study includes the determination of the kinetic parameters both during the induction phase and during the stationary phase.The above mentioned oxidations we have studied in anal$\text{o}$gous conditions in other solvents (carbon tetrachloride, benzene chloride, etc.). The highest rates observed and the larger selectivity of the fluorinated solvents have been pointed out.     

Emission spectra of supersonically cooled chloroacetylene cations

The ā²Π_Ω → X?²Π_Ω, Ω = $\text{3}\text{2}$, $\text{1}\text{2}$ emission spectra of rotationally cooled chloro- and deuterochloro-acetylene cations have been obtained by electron-impact ionisation of a seeded helium supersonic free jet. The resultant spectral improvements lead to the identification of the spin-orbit components and isotope splittings and to a vibrational assignment of the prominent bands. The vibrational frequencies could be determined to within ±1 cm^?1 for many of the fundamentals for the cations in the X?²Π_Ω and ā²Π_Ω electronic states.     

Studies on amino acids and peptides-III. 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide,LR, as a new racemization free coupling reagent in peptide synthesis

The easily accessible 2,4-bis (4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide, $\text{LR}$, has been reacted with salts of N-protected amino acids $\text{1}$ (Z-Gly-OH, Boc-Gly-OH, Boc-S-Ser(Bzl)-OH, Boc-S-Tyr(Bzl)-OH, Z-S-Arg(Z₂)-OH, and Z-S-Pro-OH), at room temperature in CH₂Cl₂ to give the intermediates $\text{2}$, mixed anhydrides. When $\text{2}$ is treated with two moles of a base and one mole of the salt of an amino acid ester $\text{3}$ (TosOH·H-Gly-OBzl, HCl·H-Gly-OBzl, HCl·H-Gly-OEt, and HCl·H-S-Phe-OtBu) at 0°C, the expected peptide $\text{4}$ is isolated in high yields. LR is also found to be a useful reagent in a fragment coupling between Z-Gly-S-Ala-OH and TosOH·H-S-Leu-OBzl). This tripeptide was tested by means of HPLC (deprotection and amino acid analysis according to Izumiya was not necessary), and no epimerization (<0.7 %) was observed.     

Substituent effects in the reaction of phenols with polyacrylonitrile radicals

Substituent effects in the reactivities of phenols towards polyacrylonitrile radicals have been studied in terms of Swain and Luptons' field (F_k) and resonance (R_k) components of the substituent parameters and the unique positional weighting factors (f_j and r_j) proposed by Williams and Norrington, with the aid of the following equation:

$\text{P}{}_{\mathrm{i}}\text{= x}{}_{\mathrm{i}}\text{?}{}_{\mathrm{i}}\text{F}{}_{\mathrm{k}}\text{+ ß}{}_{\mathrm{i}}\text{r}{}_{\mathrm{j}}\text{K}{}_{\mathrm{i}}\text{+ e}{}_{\mathrm{i}}\text{+}\text{P}\text{i}\text{o}$

P_i′s are the rate parameters, P_i⁰ being that for a standard reference compound. Two types of rate parameters have been employed—one, suggested by Simonyi, Tüdös and Pospisil (β) and another, suggested by us, (K), which is obtained from a plot of [Monomer]/(rate of polymerisation) vs [Phenol]. The correlations have been found to be quite satisfactory with both β and K. An attempt has been made to ascertain the nature of the transition state from the reaction parameters α_i and β_i; a dipolar transition state is suggested. The anomalous kinetic behaviour of hydroxy phenols has been discussed.     

Non-condon effects on radiationless triplet decay in benzene and naphthalene

Model calculations that avoid the Condon approximation are reported for T₁$\text{}\text{?}$ar S₀ intersystem crossing in normal and perdeuterated benzene and naphthalene. In both benzenes and in naphthalene-d₈, skeletal bending vibrations coupling T₁ to T₂ are found to be more efficient as accepting modes than CH-stretching vibrations.     

The polarization dependence of two-photon absorption rates for randomly oriented molecules

The method and results are presented for the analysis of the two-photon absorption experiment for randomly oriented molecules (in a single-beam regime) that can be easily extended to higher-order processes without any assumption regarding the nature of the initial state. Some known results were recovered and some new ones presented. The ratio of the averaged transition rate for circularly polarized light to the one for linearly polarized light, Ω, can be obtained from the following rules: (a) for any transition involving two states of the same symmetry (on any point group), Ω < 1: (b) exceptions to rule (a) are found in T, T_h, T_d, O and O_h groups for which A ? A transitions give Ω = 0 and E ? E gives Ω = $\text{24}\text{31}$: and (c) for any transition involving two states of different symmetry, Ω = $\text{3}\text{2}$. The results of these predictions are in excellent agreement with the available experimental data.     

X-ray study of Hg2Cl2Br2 and HgCl2HgBr2 reactions in solid state

The reactions (I) Hg₂Cl₂(s) + Br₂(g) and (II) HgCl₂(s) + HgBr₂(s) have been investigated by an X-ray method. Both the reactions yield two forms of the mixed halide HgClBr, designated as α-HgClBr and β-HgClBr. The cell parameters of the two are as follows:α-HgClBr: $\text{a = 6.196}\text{A}\text{?}$, $\text{b = 13.12}\text{A}\text{?}$, $\text{c = 4.37}\text{A}\text{?}$, z = 4, ? = 5.91 g/cm³. The powder pattern and cell parameters are similar to that of HgCl₂. Therefore it is probable that the chlorine atoms, in the linear halogenHghalogen molecules of HgCl₂ structure have been replaced by bromines, and since the radius of the bromine atom is larger than that of chlorine, the lattice is larger in this case.β-HgClBr: $\text{a = 6.78}\text{A}\text{?}$, $\text{b = 13.175}\text{A}\text{?}$, $\text{c = 4.17}\text{A}\text{?}$, z = 4, ? = 5.40. These parameters are the same as those reported in the literature for β-Hg(ClBr)₂, and its X-ray powder pattern is similar to HgCl₂. Therefore this phase also has linear halogenHghalogen molecules but the distribution of Cl and Br atoms is perhaps random.Heating the products (I) and (II) up to the melting point increases the amount of α phase and decreases the β phase, whereas crystallization increases the β phase. DTA study has supported the X-ray findings.