Time-resolved fluorescence depolarization studies of rotational relaxation in viscous media

Rotational relaxation times (τ_roi) were measured for xanthene dyes in several n-alcohols, ethylene glycol and glycerol by following the fluorescence depolarization using a single photon counting technique. Additional studies were made of the fluidity of the hydrocarbon micellar interior using pyrene derivatives as fluorescent probes. While the correlation between τ_roi and viscosity for the smaller n-alcohols is good, as anticipated by the models of Stokes—Einstein—Debye and later Perrin, a saturation in this correlation is observed in more viscous systems in accordance with recent molecular dynamics calculations. The influence of molecular structure on both viscosity and rotational relaxation times is also discussed. Pyrene, 1-pyrene suphonic acid and 1-pyrene butyeric acid exhibit rapid reorientation τ_roi ? 10^?9 s, in glycerol and micellar systems.     

Rapid computer simulation of ESR spectra. Conventional ESR of axially symmetric 14N-nitroxide spin labels

A computer algorithm is presented for the simulation of the effect of molecular tumbling on ESR spectra, and is applied to simulation of the conventional ESR signal (the absorption signal detected at the first harmonic of the modulation frequency and in-phase with the modulation frequency, in the limit of low microwave and modulation power) of axially symmetric ¹⁴N-nitroxide spin labels. The algorithm is extremely fast and is economical in terms of computer memory requirements.     

Dicyclopentadienyl-η1-cyclooctatrienyltitanium and dicyclopentadienyl-η3-cyclooctatrienylniobium

Dicyclopentadienyl-η¹-cyclooctatrienyltitanium and -η³-cyclooctatrienylniobium are prepared from (C₅H₅)₂MCl₂ (M = Ti, Nb) and two equivalent amounts of i-PrMgCl in the presence of an excess of cyclooctatetraene. For the preparation of (C₅H₅)₂NbC₈H₉ the presence of NaBH₄ is also necessary. The products obtained are characterized by IR, mass and ¹H NMR spectroscopy. Reactions with HCl, thermal decomposition reactions, magnetic measurements and elemental analyses were performed to establish the structures.     

Reaction of carboxamide with Cu2Oisonitrile complex; formation of a new chelated copper(I) complex

Reaction of carboxamides with Cu₂O in the presence of t-butyl isocyanide gave new chelated copper(I) complexes, which probably are formed by the insertion of t-butyl isocyanide into the coppernitrogen bond of copper(I) amide isonitrile complexes, which were initially produced from the carboxamides and Cu₂Ot-butyl isocyanide complex. The same chelated copper(I) complexes were prepared more readily by the reaction of the corresponding N-trimethylsilyl-carboxamides with Cu₂Ot-butyl isocyanide complex. Reactions of the copper(I) complexes thus obtained with alkylating agents, such as alkyl halides, alkyl tosylates and triethyloxonium tetrafluoroborate, also were described.     

Attempts to prepare alkylidene zirconium complexes by α-hydrogen atom abstraction

We prepared several new neopentyl halide complexes of zirconium in order to test whether they could be induced to lose neopentane and give neopentylidene complexes by adding phosphorus or nitrogen donor ligands. ZrNp₂X₂ (X  Cl or Br) can be prepared in ether and isolated as a dietherate (an oil). It reacts with L (L  PMe₃, PMe₂Ph, NEt₃, $\text{1}\text{2}$ DMPE, $\text{1}\text{2}$ TMEDA) to give ZrNp₂X₂L₂. ZrNp₃Cl can be prepared by adding MgNp₂ to ZrNp₂Cl₂(ether)₂ and isolated by sublimation in 25% yield. On adding PMe₃ or TMEDA, it disproportionates to ZrNp₄ and ZrNp₂Cl₂L₂. ZrCp″NpCl₂ (Cp″ = η⁵-C₅Me₅), ZrCp″Np₂Cl, and ZrCp″Np₃ were prepared by adding MgNp₂ to ZrCp″Cl₃. Only the last is a solid, only the first forms an adduct, ZrCp″NpCl₂(PMe₃). None of the complexes decomposed to tractable products in the presence of L. Photolysis of ZrNp₂Cl₂(PMe₃)₂ yielded [Zr(PMe₃)₂Cl₃]₂ by an apparently complex reaction initiated by homolytic ZrNp bond fission.     

Side chain modified sterols as probes into insect molting hormone metabolism. I: synthesis of monofluorophytosterols

25- and 26-monofluorophytosterols were synthesized from stigmasterol as potential arthropod-activated competitive inhibitors of side chain hydroxylations occuring in ecdysone biogenesis.     

Sesquiterpenes from termite soldiers. Structure of amiteol,a new 5β, 7β, 10β-eudesmane from amitermesexcellens

The defense secretions of termite soldiers in the genera $\text{Amitermes}$, $\text{Noditermes}$, and $\text{Prorhinotermes}$ contain sesqueterpene hydrocarbons, alcohols and ethers. Three new eudesmanes possessing the hitherto unknown 5β, 7β, 10β configuration were identified from $\text{Amitermes}$$\text{excellens}$.     

Preparation and properties of the formamidino complexes [M(π-C5H5){HC(NR)2}(CO)2] (M = molybdenum or tungsten; R = aryl or alkyl)

The preparation and properties of the complexes [M(π-C₅H₅){HC(NR)₂}CO)₂] (M = Mo, W; R = aryl or alkyl) are reported. The complex [Mo(π-C₅H₅){HC(N-p-tolyl)₂}(CO)₂] could be prepared by (a) reaction of MoCp(CO)₃Cl with M′{HC(N-p-tolyl)₂} (M′ = K, Ag or Cu); (b) irradiation of MoCp(CO)₃Cl with HC(HN-p-tolyl)N-p-tolyl); and (c) reaction of [MoCp(CO)₃]₂ with M′{HC(N-p-tolyl)₂} (M′ = Ag or Cu). The several routes to this complex give indications of the mechanisms of formation. The structure of these complexes and the bonding nature of the metal with the formamidino group is discussed on basis of the ¹H and ¹³C NMR and IR spectra.Reaction of N,N′-dimethyl formamidine with MCp(CO)₃Cl gave the complex [M(π-C₅H₅){HC(NMe)N(CO)Me}(CO)₂], containing a carbonyl inserted between the metal and the formamidino group. Irradiation of this carbamoyl complex caused decarbonylation, yielding the complex [M(π-C₅H₅){HC(NMe)₂}CO)₂].     

Polynuclear isocyanide complexes of rhenium

The arylation of carbonylgold chloride with diarylzinc compounds yields either triarylgoldzinc or diarylgoldzinc chlorides, depending on the reactant ratio and the nature of the aryl group. The same reactions with diphenylcadmium and diphenylmercury yield exclusively diphenylgoldcadmium chloride and diphenylgoldmercury chloride, respectively. The reactions of the products with N,N,N′,N′-tetramethylethylenediamine and triphenylphosphine were studied.Phenylgold has been obtained as a very unstable solid from diphenylgoldzinc chloride and diphenylgoldmercury chloride.     

Interpretation of the vibrational spectra of methylglyoxal and biacetyl in their first singlet excited electronic states

Laser-induced fluorescence spectra for the first allowed electronic transition (22125 cm^?1) of methylglyoxal (CH₃COCHO) and its perdeutero analog (CD₃COCDO) in a supersonic nozzle beam are quantitatively represented assuming that the potential function governing the CH₃(CD₃) rotation is changed during the transition. In the excited state the potential function is ternary (V₁ = 95 (1 + cos 3θ)cm^?1) as in the fundamental state (V₀ = 134.5 (1 - cos 3θ)cm^?1), but the minima are shifted by an angle of π/3. The spectrum of biacetyl (CH₃COCH₃CO) can be reproduced assuming two uncoupled methyl groups undergoing similar conformational changes during the electronic transition (the estimated potential function is V₁ = 117.5 (1 + cos 3θ) cm^?1 for each methyl group), in perfect agreement with the most recent assignment of the 0-0 transition. These results are consistent with ab initio calculations for the fundamental and first excited singlet states.     

Directed 2-azonia-[3,3]-sigmatropic rearrangements. a convenient preparation of substituted 1-azaspiro[4,5]decanes

3-Acetylpyrrolidines are prepared from 5-methyl-5-vinyloxazolidines in a reaction which involves a directed 2-azonia-[3,3]-sigmatropic rearrangement.     

The He-I photoelectron spectra of uranocene and thorocene

The bonding in unranocene and thorocene is discussed in the light of their photoelectron spectra and ionization of 5f electrons is identified.     

On the vibrational spectra of liquid HCl

We report quantitative measurements of the infrared spectra intensities and of the Raman cross section for liquid HCl. The local field effect and the induced dipole moment account for the observed intensity enhancement. Our calculation is based on the reaction field approach. On the other hand, we show that the local field effect and the dipolar term in the intermolecular interaction energy are not sufficient to explain the frequency shift. We also show that the first overtone is mainly due to simultaneous transitions of two molecules from the ν = 0 to the ν = 1 levels and our calculations give the right order of magnitude of its intensity. Finally, we can reproduce the lineshape of the first overtone by a dissipative coupling which is derived from Redfield's theory of relaxation.     

The effects of sample preparation,pyrolysis and pyrolyzate transfer conditions on pyrolysis mass spectra

Two different biopolymers, bovine serum albumin and glycogen, were examined by pyrolysis-mass spectrometry under various experimental conditions. The parameters tested include the method of cleaning the pyrolysis wire, the choice of the sample solvent, the sample size, the temperature-time profile and the temperature of the mass spectrometric inlet system.In order to determine quantitatively the effects of changes in experimental conditions on reproducibility of the spectra, the differences observed between the pyrolysis mass spectra represented as numerical dissimilarity values.It is concluded that the long-term differences observed are only partly explained by fluctuations in the conditions studied. However, it appears feasible to define a set of standard conditions with respect to the production of the pyrolyzate which should afford a reasonable degree of interlaboratory reproducibility.     

The vibrational spectrum of (maleic anhydride)iron tetracarbonyl

On the basis of solid-phase IR and Raman spectra, with some solution data for the IR, a reasonably complete vibrational assignment has been made for the modes of maleic anhydride in (maleic anhydride)iron tetracarbonyl. Shifts in v(C=C) and δ(CH) are consistent with a strong interaction with the metal, but relatively little coupling between the modes. More restricted assignments were made for modes associated with the (maleic anhydride)iron and Fe(CO)₄ fragments.     

Raman and infrared spectra of lanthanum molybdate

The infrared and Raman spectra of gel-grown lanthanum molybdate were recorded. Group theoretical analysis was carried out and a vibrational assignment proposed based on C_2h symmetry. Factor group and site effects are discussed.