Synthesis of ring modified prostaglandins

The total syntheses of the ring modified prostaglandins 8–12, 16, 18, 20, and 22 are described.     

The coulometric titration of tetraphenylborate ion with electrogenerated silver ion and a biamperometric end-point : Application to the determination of potassium and polyethyleneglycols

Microequivalent amounts of TPB in a 40% acetone generating electrolyte were titrated with coulometrically generated silver ions. With a biamperometric endpoint, samples of 0.1–4 μeq of NaTPB were determined with a precision with 1%. The technique was applied to the determination of potassium in potassium chloride alone and in mixtures with other salts.The overall accuracy ranged from -3 to -7% for samples of 4 μeq to 1 μeq of potassium, respectively. Artificial serum samples gave somewhat discordant results, because of difficulty in removing all interfering protein. A method was developed, for the determination of 0.1–1.0 mg of PEG 600 to 4000 with excess TPB in the presence of barium ions. With reasonable care errors may be held to within 5%.     

The NMR spectra of porphyrins—14: Self-aggregation of zinc(II) meso-nitro and meso-dinitro octaethylporphyrins

Complex formation in zinc(II) meso-nitro-octa-ethylporphyrin (1) and the corresponding α,β-dinitro (2) and α, γ-dinitro (3) zinc(II) chelates has been studied using proton NMR at 220MHz. This allows complete resolution of all the distinct groups in the proton spectrum, and the large concentration dependence of the spectra of 1 and 2 can be analysed to afford the monomeric and monomer-dimer shifts for all protons in these molecules. In contrast 3 shows no concentration dependence, nor any change upon addition of pyrrolidine, which immediately dissociates the aggregates of 1 and 2. The monomeric ¹H and ¹³C shifts are reported, together with those of zinc(II) octaethylporphyrin (4), and the complete assignment given allows the substituent shifts of the meso nitro groups in the porphyrin to be obtained. Analysis of the monomer-dimer shifts in terms of the ring current model gives the detailed geometries of the dimers, which have an inter-ring separation of ca 4.5 Å and a lateral displacement from the vertical of ca 1.0 Å. The results also allow the distinction between two different molecular complexes considered previously, and fully confirm our earlier suggestions that binding is due to metal-to-porphyrin, rather than metal-to-substituent, interactions.     

Microwave spectrum and substitutional structure of CH2DF

Forty-two transitions of the microwave spectrum of CH₂DF have been observed in the region between 75 and 450 GHz. The measurement of both a-type and b-type transitions makes possible the analysis of the spectrum and the accurate calculation of the rotational constants (in MHz): = 119 675.0535 ± 0.074, = 24 043.4415 ± 0.072, ? = 22959.3732 °0.072, °j = 0.049371 ±0.00011, °_jk = 0.34268 ±0.0006, 2_k = 3,3774 ± 0.0035, δ _j = 0.002329 ± 0.000045, δ_k = 0.0687 ± 0.036. These constants, in combination with the results of earlier work on the symmetric speci r_s structure calculation based entirely on high-accuracy microwave data. The structural parameters are r_CH = 1.100 Å, r_CF = 1.383 Å, and ∠HCH = 110° 37'.     

Construction of small data bases for trace element determinations

Construction of a small data base intended as a model for personal use in the area of trace element determinations is described. A MELCOM 7000 computer is used and several types of on-line conversational retrieval systems are discussed.     

The crystal structure of bicyclo [3.3.3]undecane-1,5-diol and the conformation of bicyclo[3.3.3]undecane (manxane)

The crystal structure of bicyclo [3.3.3]undecane-1,5-diol has been determined. It is monoclinic, P2₁/c, a = 12.99(2), b = 14.16(2), c = 12.50(1)A,β = 112.42(2)°, with two independent molecules in the asymmetric unit. One of these is disordered, but the other has almost exact C_3h symmetry and its conformation and precise molecular geometry agree well with previous calculations by molecular mechanics. The molecule shows considerable angle strain, having bridge angles in the range 118–121°     

Bile pigment studies—III: Controlled oxidative degradation of 1,19(21,24h)-bilindiones (bilitrienes)

Treatment of the model 1,19(21,24$\text{H}$)-bilindione (1) with thallium(III) acetate in methanol gives the thallium(III) complex (11) which is unstable and in the presence of air and methanol is transformed into the 15,16-dimethoxy complex (12), characterised as the metal free derivative (13). When exposed to light, solutions of (12) are oxidised to afford, after work-up, the 14-formyl-1(15$\text{H}$)-tripyrrinone (4) and ethylmethylmaleimide (17). A general discussion of mechanistic implications is presented.     

Distortion of the coordination polyhedron in mononuclear copper(II) complexes. Optical absorption and electron spin resonance studies on some five-coordinate copper(II) complexes

The preparation and spectral properties are reported for a series of ten mixed-ligand copper(II) complexes of the form [Cu(A)(B)_n](X), where A is acetylacetonate anion, B represents a mono- or bidentate ligand such as morpholine, piperidine, isonicotinic acid hydrazide, 2,2′-bipyridine, 1,10-phenanthroline and X is variously NO^?₃ or ClO^?₄ anion and n = 1 or 2. The coordination of the anions and ligands has been demonstrated by infrared and electronic spectral methods. Electron spin resonance spectral data show the square-pyramidal five-coordinated arrangement around copper(II) in these complexes. Parameters such as g₆, g_⊥, A₆, A_⊥, 〈g〉 and 〈A〉 calculated from electron spin resonance data in solid and solution state at room temperature as well as frozen solution indicate the presence of the unpaired electron in the d_x2_?y2 or d_z2 orbital. These results are in good agreement with electronic and photoacoustic spectral studies.     

On the contributions of resonance,hybridization and nonbonded interactions to the structure of butadiene

A recent ab initio molecular orbital calculation on butadiene has been interpreted by Skaarup, Boggs and Skancke as indicating that the shortness of the central C-C bond is due primarily to hybridization. Resonance was considered to make a minor contribution and nonbonded interactions were judged to be unimportant. Unfortunately, this analysis failed to take into account the crucial role of geminal nonbonded interactions, and the calculations were, accordingly, not designed to discriminate between the hybridization and nonbonded models. A more direct investigation of intramolecular nonbonded interactions based on ab initio computations has been earned out on other systems, however, providing evidence that the effects of nonbonded contributions are substantial.     

The molecular structure and conformation of gaseous bis(chloromethyl)dimethyl silane as determined by electron diffraction

The molecular structure of bis(chloromethyl) dimethyl silane has been investigated in the gas phase at a nozzle temperature of 60° C. The molecules exist mainly in the GG form with the presence of 30% (+10%, ?20%) AG form. The values of the principal distances (r_a) and angles with estimated error limits of 2σ are r(C-H) = 1.093 (0.009) Å, r(C-Cl) = 1.801 (0.019) Å, r(Si-C) (the average Si-C bond) = 1.875 (0.009) Å, ∠(CSiC) = 109.5°, ∠(SiCCl) = 110.5° (0.4), ∠(CCH) = 112.5° (1.8) and φ (the gauche torsion angle relative to 0° for the anti form) = 117.4° (3.8).     

Supernucleophiles—II: Orbital interactions and nucleophilicity

The role of adjacent lone pair centers upon the nucleophilic reactivity of various amines with p-nitrophenyl acetate has been studied. The kinetics of appropriately substituted hydroxy- and methoxyamines, as well as unsubstituted analogs are presented. The effect of orbital orientation was evaluated theoretically for 1-aminoethanol using CNDO/2. The results of the theoretical study imply a small through-bond and an even smaller through-space lone pair interaction. Kinetically, rate enhancements resulting from such interactions are not observed.     

Molecular structure and conformation of 2,3-dichloro-1-propene as determined by gas-phase electron diffraction

The molecular structure and conformation of 2,3-dichloro-1-propene have been determined by gas-phase electron diffraction at nozzle temperatures of 24, 90 and 273°C. The molecules exist as a mixture of two conformers with the chlorine atoms anti (torsion angle ∠φ = 0°) or gauche (∠φ = 109°) to each other and with the anti form the more stable. The composition (mole fraction) of the vapor with uncertainties estimated at 2σ was found to be 0.55 (0.08), 0.49 (0.08) and 0.41 (0.10) at 24, 90 and 273°, respectively. These values correspond to an energy difference with estimated standard deviation ΔE° = E°_g-E°_a = 0.7 ± 0.3 kcal mol^?1 and an entropy difference ΔS° = S°_g-S°_a = 0.6 ± 0.9 cal mol^?1 K^?1. Some of the diffraction results, together with spectroscopic observations, permit the evaluation of an approximate torsional potential function of the form 2V = V₁ (1 - cos φ) + V₂ (1 - cos 2φ) + V₃ (1 - cos 3φ); the results are V₁ = 4.4 ± 0.5, V₂ = ?2.9 ± 0.5 and V₃ = 4.8 ± 0.2, all in kcal mol^?1. The results at 24°C for the distance (r_a) and angle (∠_α) parameters, with estimated uncertainties of 2σ, are: r(C_sp²-H) = 1.098(0.020)Å, r(C_sp³-H) = 1.103(0.020)Å, r(CC) = 1.334(0.009)Å, r(C-C) = 1.504(0.013)Å, r(C_sp²-Cl) = 1.752(0.021)Å, r(C_sp³-Cl) = 1.776(0.020)Å, ∠C-CC = 127.6(1.1)°, ∠C_sp³-C_sp²-Cl = 110.2(1.0), ∠C_sp²-C_sp³-Cl = 113.1(1.2)°, ∠H-C_sp³-H = 109.5° (assumed), ∠CC-H = 120.0° (assumed) and ∠φ = 108.9(3.4)°.     

Vibrational spectra and molecular configuration of hexafluoroazomethane

Twenty-one of the 24 fundamental frequencies of CF₃N=NCF₃ have been identified from the infrared and Raman spectra of the vapor and condensed states. The spectra reveal a total lack of infrared-Raman coincidence, i.e., the rule of mutual exclusion is obeyed. This evidence strongly supports the existence of hexafluoroazomethane in the trans configuration and negates the results of a recent electron diffraction study which favor the cis form.     

An ab initio MO calculation of the electronic structure and geometry of protonated methanol

Protonated methanol, CH₃ OH₂⁺, has been studied using the LCAO—MO—SCF method with a 7, 3 and 9, 5, 1 Gaussian orbital basis set on the heavy atoms and 4s on hydrogen. It is found that the ground state is non-planar around oxygen, in contrast with previous calculations, with an inversion barrier of 3 kcal mol^?1. The changes in electron distribution in the reacting systemCH₃⁺ + H₂O → CF₃OH₂⁺is also examined.     

Vapor phase infrared spectrum and coriolis coupling constants of pentacarbonyl(thiocarbonyl)chromium(0)

Several band contours have been successfully resolved in the high-resolution IR spectrum of pentacarbonyl(thiocarbonyl)chromium(0) vapor at ~312 K. However, PQR separations are only clearly discernible for the three v(CO) fundamentals (v₁,v₂ and v₁₆). The good agreement between the observed and calculated PR separations of the two a₁v(CO) modes (v₁ and v₂) verifies the C_4v prolate symmetrical top geometry of the molecule. From band shape analyses, the Coriolis coupling constants of the ev(CO) mode (v₁₆) and the e δ (CrCO) mode (v₁₇) are estimated to be —0.45 ± 0.05 and —0.80 ± 0.15, respectively.     

Vibrational spectra of ethyl iodedes

The infrared spectra of CH₃CH₂I, CD₃CH₂I, and CH₃CD₂I of the vapors and the solids at 170°C have been recorded from 4000-200 cm^?1. The Raman spectra of the liquids and vapors have also been recorded and depolarization values have been measured. Assignment of the eighteen fundamental vibrations has been based on depolarization values, band contours, group-frequency correlations, and normal coordinate calculations. A critical discussion of the CH stretching assignments in CH₃CH₂X molecules is presented.     

Some observations concerning the direct titration of nitrite with cerium(IV)

Direct titration of nitrite with cerium (IV), with ferroin as indicator, is shown to give satisfactory results if the acidity is kept between 0.033 and 0.055M at the end-point. Loss of nitrous acid owing to volatilization and decomposition is discussed. From 10 to 60 mg of sodium nitrite can be estimated with a standard deviation of 5 mug and an average error of 0.2%.     

Some observations on the interdependence of cyanide concentration and atomization efficiency in the nitrous oxide-acetylene flame

A relationship is derived between CN concentration and atomization efficiency in the C₂H₂-N₂O flame. The relationship is examined under various experimental conditions and β values are estimated for a number of elements. The possibility of complex vapour phase oxide formation by U is considered.     

The separation of mercury from gold by ion exchange

Mixtures containing large amounts of gold and small amounts of mercury (50:1) can be quantitatively separated by passing a 2N hydrochloric acid solution of the chlorides through Dowex 50 resin. Mercury behaves as a cation and is quantitatively retained. Gold behaves as an union and is not retained by the resin. The gold is obtained spcctrobcopically free from all metals. The capacity of the resin is approximately 10 nig of mercury per gram of rebin. The rcyin is freed from mercury by washing with 2N liydroclonc acid and may be used over again.