Chelating properties of n,n,n,n-tetrakis-(phosphonomethyl)-1,2-cyclohexanediamine

The octasodium salt of N,N,N',N'-tetrakis-(phosphonomethyl)-1,2-cyclohoxanediamine, Na₈-CDTMP, can be prepared in 45% yield from chloromethylphosphonic acid and 1,2-cyclohexanediamine. The titration curve resulting from the titration of the acid, CDTMP, with sodium hydroxide at 25° and μ = 0.1 was used to estimate the eight pK values for the free acid. The stability constants of metal chelatles of CDTMP were measured at 25° and μ = 0.1 potentiometrically.     

A Theoretical Study of LiHe+ n , NaHe+ n , and MgHe+ n Complexes, with n=1, 2, 3, 4

The LiHe⁺ _n , the NaHe⁺ _n , and the MgHe⁺ _n complexes with n=1, 2, 3, 4 were studied using ab initio calculations with the MP2/6-311+G(3df, 3pd) method. The complexes are found to be stable. For the n=1 complexes, previous results were available and the calculations performed are in good agreement with those results. This lends credibility to the results obtained for the complexes with higher n.     

Dianion metallation reactions of n,n-dimethylvanillylamine and n,n-dimethylisovanillylamine

The utility of dianion chemistry in the synthesis of polyfunctional aromatics is demonstrated by the direct lithiation of the vanillylamine 1 and by the metal-halogen exchange reaction of the bromo isovanillylamines 9 and 10.     

Activation cross-sections for some (n, 2n), (n,p) and (n, γ)-reactions

The average fission neutron cross-sections of the reactions²³³U(n, 2n)²³²U,⁶⁰Ni(n, p)⁶⁰Co and²⁷Al(n, p)²⁷Mg and the resonance integrals of the (n, γ)-reactions of the nuclides¹⁸¹Ta,¹⁷⁶Lu,¹⁷⁵Lu,⁶⁴Ni,⁵⁹Co and²⁶Mg have been determined by the activation method following the well-known conventions. The results verify some of the existing values and present data for hitherto unknown or poorly known reactions.     

Local aromaticity of [n]acenes, [n]phenacenes, and [n]helicenes (n = 1-9)

The local aromaticity of the six-membered rings in three series of benzenoid compounds, namely, the [n]acenes, [n]phenacenes, and [n]helicenes for n = 1-9, has been assessed by means of three probes of local aromaticity based on structural, magnetic, and electron delocalization properties. For [n]acenes our analysis shows that the more reactive inner rings are more aromatic than the outer rings. For [n]phenacenes, all indicators of aromaticity show that the external rings are the most aromatic. From the external to the central ring, the local aromaticity varies in a damped alternate way. The trends for the [n]helicene series are the same as those found for [n]phenacenes. Despite the departure from planarity in [n]helicenes, only a very slight loss of aromaticity is detected in [n]helicenes as compared to the corresponding [n]phenacenes. Finally, because of magnetic couplings between superimposed six-membered rings in the higher members of the [n]helicenes series, we have demonstrated that the NICS indicator of aromaticity artificially increases the local aromaticity of their most external rings.     

(2n,n) potential and sticky-sphere fluids

The authors investigate the behavior of a model fluid for which the interaction energy between molecules at a separation r is of the form 4epsilon[(sigma/r)2n-(sigma/r)n], where epsilon and sigma are constants and n is a large integer. The particular properties they study are the pressure p, the mean square force F2, the elastic shear modulus at infinite frequency Ginfinity, the bulk modulus at infinite frequency Kinfinity, and the potential energy per molecule u. They show that if n is sufficiently large it is possible to derive the properties of the system in terms of two parameters, the values of the cavity function and of its derivative at the position r=sigma. As an example they examine in detail the cases with n=144 and n=72 for three different temperatures and they test the theory by comparison with a computer simulation of the system. They use the simulated pressure and the average mean square force to determine the two parameters and use these values to evaluate other properties; it is found that the theory produces results which agree with computer simulation to within approximately 3%. It is also shown that the model, when the parameter n is large, is equivalent to Baxter's sticky-sphere model with the strength of the adhesion determined by the value of n and the temperature. They use Baxter's solution of the Percus-Yevick equations for the sticky-sphere model to determine the cavity function and from that the values of the same properties. In this second approach there are no free parameters to determine from simulation; all properties are completely determined by the theory. The results obtained agree with computer simulation only to within approximately 6%. This suggests that for this model one needs a better approximation to the cavity function than that provided by the Percus-Yevick solution. Nevertheless, the model looks promising for the study of (typically small) colloidal liquids where the range of attraction is short but finite when compared to its diameter, in contrast to Baxter's sticky-sphere limit where the attractive interaction range is taken to be infinitely narrow. The continuous function approach developed here enables important physical properties such as the infinite shear modulus to be computed, which are finite in experimental systems but are undefined in the sticky-sphere model.     

Gram-Scale Synthesis of the 1,1,n,n-Tetramethyl[n](2,11)teropyrenophanes

A gram-scale synthesis of a series of 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes (n=7–9) has been accomplished as well as the first synthesis of the next higher homologue 1,1,10,10-tetramethyl[10](2,11)teropyrenophane. The scale-up of the original small-scale synthesis required the development of several heavily modified synthetic methods, including a chlorination/Friedel–Crafts alkylation protocol and an iodination/Wurtz coupling protocol, which were performed on 25–30 g and 30–60 g scales, respectively. Two separate sets of conditions for the key teropyrene-forming cyclodehydrogenation reaction at the end of the synthetic pathway were developed, an acid-promoted one for the two less strained congeners and an acid-free method for the two more strained homologues.     

Systematic study of (Na n )2 dimer transient state in Na n +Na n collisions (n=8, 9, 19, and 20)

From distance dependent tight-binding molecular dynamics simulations, we systematically study the Na _n +Na _n collision dynamics around the first two closed shells (n=8 and 20). We investigate the stability of sodium cluster dimers (Na _n )₂, for many events with random relative orientation at finite temperature, various impact parameters and incident energies. We find that (Na₈)₂, (Na₉)₂, (Na₁₉)₂ and (Na₂₀)₂ can exist during about 3000 fs in central collisions while they can exist up to about ten thousands fs in peripheral collisions with larger impact parameters in fusion mechanism at c.o.m energy per atomE _cm/n=0.025 eV. We observe that the lower the incident energy, the longer the lifetime of the cluster dimers in both central and peripheral collisions. There is no apparent difference in the dynamical stability of (Na₈)₂ and (Na₉)₂, (Na₁₉)₂ and (Na₂₀)₂ although (Na₈)₂ and (Na₂₀)₂ are respectively slightly colder than (Na₉)₂ and (Na₁₉)₂ for the same incident energy per atom and the same impact parameter.     

Syntheses, structures, spectroscopic properties, and pi-dimeric interactions of [n.n]quinquethiophenophanes

A cyclophane-type of dimeric quinquethiophenes (4a-e) with the bridge chains consecutively varying from two to six methylenes has been synthesized and studied as ideal pi-dimer models. The double-decker structures of these compounds are verified by upfield shifts for the proton NMR signals of the inside thiophenes, as compared to those of monomeric dimethylquinquethiophene (3). The electronic absorption and emission spectra of 4a-e are perturbed by through-space pi-electronic interactions involving exciton-exciton coupling between the two overlapped quinquethiophenes, which become marked with shortening of the bridged alkylene chains. One-electron oxidation of 4a-e with FeCl(3) in dichloromethane results in the appearance of specific polaronic bands in the near-infrared region of the electronic absorption spectra, due to the generation of a radical cation species (polaron) on one of the quinquethiophenes, which electronically interacts with the remaining neutral species. Two-electron oxidation of 4a-e introduces spectral changes, revealing that the resulting two quinquethiophene radical cations readily form an intramolecular pi-dimer, thanks to their close stacking, in contrast to the difficult formation of an intermolecular pi-dimer from 3. The pi-dimeric spectra of 4b-e are comprised of two strong absorption bands, similar to that of 3, the low-energy band of which is considerably red-shifted by an effective pi-dimeric interaction depending on the lengths of the bridged alkylene chains. Quite different is the spectrum of 4a with three absorption bands inherent in pi-dimer, presumably because the two short bridging chains of 4a force the pi-dimer to take a constrained, strongly interactive structure.     

Electron impact ionization of silver clusters Ag n,n≦36

Electron impact ionization of gas phase silver clusters Ag _n ,n≦36 has been achieved in the threshold region. The vertical ionization potentials in this region clearly demonstrate the evidence of shell effects as well as a distinct even-odd oscillation up ton?20. Their general size dependence is somewhat different from that of the alkali metal clusters due to the presence of thed-electrons.     

Molybd?n, Wolfram

Ohne Zusammenfassung     

Epithermal neutron activation analysis using (n,n′) reaction

The (n, n′) reaction with the epithermal and fast neutrons of a nuclear reactor has been studied for activation analysis of Sr, Cd, In, Ba, Hf, Os, Au, Hg and Pb. For some elements (In, Os, Au, Hg and Pb) the use of a cadmium sheet reduced the activity by less than a factor of two, while the interferences from the most abundant elements have been reduced by more than two orders of magnitude.     

Determination of the103Rh/n, 2n/102Rh and103Rh/n, 2n/102mRh reaction cross-section,averaged over a fission spectrum

The instrumental determination of the¹⁰³Rh/n, 2n/¹⁰²Rh and¹⁰³Rh/n, 2n/^102mRh reaction cross-sections was carried out averaged over a fission spectrum. The experimental procedure is described and the results are discussed, in comparison with previous published data.     

LaC4^n（n=—2,—1,0,＋1,＋2）分子簇的结构与稳定性

本文用密度泛函方法研究了ＬａＣ４ｎ（ｎ＝－２,－１,０,＋１,＋２）分子簇的结构与稳定性。振动频率分析表明,在所提出的九个构型中,当ｎ＝－２,０,＋１,＋２时,稀土位于碳环上最稳定,而当ｎ＝－１时,尽管稀土位于碳环上能量最低,但没有找到稳定的构型,我们的结果还指出,稀土元素是分子簇中对外部环境最敏感的部位,即最具有反应活性     

Fast non-destructive determination of silicon in coal by means of /n,n′ γ/ and /n, γ/ processes

The possibilities were evaluated of nondestructive determination of silicon content in large-scale samples of coal /about 20–50 kg/, based on the spectrometry of prompt -radiation from processes /n, n /, E=1779 keV and /n, /, E=3539 keV and 4935 keV. The neutron sources were either²⁴¹Am–Be or²⁵²Cf located additionally in D₂O moderator. A Ge/Li/ detector was used for -radiation detection. In exposure times of up to 2 h, the detection limits of 1.3% and 0.9% and accuracies of silicon determination of 0.66% and 0.40% have been achieved in case of /n, / and /n, n / processes, respectively.