Role of the supramolecular structure of the reactants in the kinetics of the liquid-phase synthesis and decomposition of explosives

Formulas relating the observed rate constant of the initial reaction step (k _ef) to the rate constants of the elementary steps (k _i ), to the monomer-association species equilibrium constants (K _i ), and to the concentrations of the reactants (A _i ) and solvent have been obtained for a number of simple kinetic models of liquid-phase explosive material synthesis and decomposition reactions involving associating reactants. The k _ef = F(k _i , K _i , and A _i ) relationship is independent of the rate law of the reaction and is governed by the association species type (autoassociation or heteroassociation species) and by the number of association species kinds. In the case of parallel reactions involving association species, as distinct from the same reactions involving unassociated reactants, concentration variations have an effect on the ratio of the rates of the parallel steps and on the product yield ratio. By varying the reaction temperature, it is possible to make the rates of the parallel steps to vary in opposite ways. When monomers, dimers, and tetramers are present in the reaction mixture, the temperature dependence of lnk _ef may have an extremum. These deduced regularities are in qualitative agreement with experimental data.     

Relation of the decay of free radicals in irradiated polyethylene to the molecular motion of the polymer and the configurations of the free radicals

Decay reactions of the free radicals produced in irradiated polyethylene (high-density and low-density materials) were examined in connection with the molecular motion of the matrix polymer. Three temperature regions, in which the free radicals decay very rapidly, at around 120, 200, and 250°K, were designated T_A, T_L, and T_B, respectively. The decay of the free radicals at these temperatures had activation energies in high-density polyethylene of 0.4 kcal/mole for T_A, 9.4 kcal/mole for T_L, and 18.4 kcal/mole for T_B. In low-density polyethylene these quantities were 0.7 kcal/mole for T_A, 23.1 kcal/mole for T_L, and 24.8 kcal/mole for T_B. Comparison of time constants for the decay reactions and for molecular motion of the matrix polymer indicate that the decay in T_A and T_B is closely related to molecular motion in the amorphous regions of the polymer. The decay of the free radicals at T_L in high-density polyethylene is due to molecular motion associated with local mode relaxation at lamellar surfaces, while that of low-density polyethylene is due to local mode relaxation in the completely amorphous region. Steric configurations of the free radicals which decay in the respective temperature regions were also investigated.     

On the structure of the diagonal conditions

Some structural features of the diagonal problem of reduced density matrix theory are investigated by considering the cone B^r introduced elsewhere. In some special cases, we discover a very tight connection between the group structure of G^r, the invariance group of B^r, and the convex structure of B^r. We also state a general theorem that relates the convex structure of B^r to the group structure of G^r.     

To the Understanding of the Structural Sensitivity of the Temperature Coefficient of Internal Pressure

The previously found empirical relationships between the temperature coefficient of internal pressure, on the one hand, and the structure and its evolution in liquids due to variations of temperature and concentration, on the other, are interpreted in terms of the peculiarities of intermolecular interactions. Analysis has revealed that the curves of the temperature dependences of internal pressure P _i(T) of associated liquids are directed upward by their concavity; they have a minimum and asymptotically tend toward P _i = 0 at T→∞. The curves P _i(T) of weakly associated liquids are directed downward by their concavity and have no extrema, but asymptotically tend to zero at T→∞.Original Russian Text Copyright © 2004 by V. N. Kartsev__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 877–882, September–October, 2004.     

Investigation of the Chemo- and Stereoselectivity of the Ketene-Claisen Rearrangement

A novel type of ketene-Claisen rearrangement in which the precursor of the rearrangement is generated in situ by reaction of optically active allyl thioethers with dichloroketene is described. A characteristic feature of this rearrangement is the excellent chemoselectivity in favor of allyl thioethers vs. allyl ethers, i.e., exclusive chirality transfer of the allylic sulfur moiety is observed with 12, 13 , and 25--27 . The cyclic, optically active allyl thioethers (+)-(R)- 4 and (?)-(S)- 4 and the open-chain allyl thioethers 11--13 rearrange with in situ generated dichloroketene to the optically active thioesters (?)-(S)- 28 , (+)-(R)- 28 , and 31-33 , respectively. A chirality-transfer of > 99% in the cyclic cases (+)-(R)- 4 and (?)-(S)- 4 , and 96--98 % in the open-chain cases 11--13 is observed. Furthermore, the dichloroketene-Claisen rearrangement is characterized by a high asymmetric 1,2-induction. The chiral allylic sulfides 25--27 give the optically active thioesters 36--38 with a 1,2-induction > 99% as determined by NMR-shift experiments.     

On the optimal mixing of the exchange energy and the electron-electron interaction part of the exchange-correlation energy

The optimal mixing coefficient C of the exchange energy E_x and the electron-electron interaction part of the exchange-correlation energy W¹_xc in the formula for the total exchange-correlation energy E_xc was expressed through the ratio of the kinetic T_c and potential W_c contributions to the correlation energy E_c. This expression can be derived from a Heavyside step function model of the dependence of W^λ_xc on the coupling parameter of the electron interaction λ. Values of T_c and W_c obtained from ab initio wave functions were used to estimate C for a number of atoms and molecules. A strong dependence of T_c, W_c, and C on the bond distance was demonstrated for the case of the H₂ molecule. T_c and C approach zero in the bond-dissociation limit; so for an electron-pair bond, the admixing of exact exchange to obtain an accurate E_xc is strongly dependent on the bond length and has to disappear for weak interaction/large bond distances. The potential of the exchange-correlation hole constructed for H₂ from an ab initio second-order density matrix was compared with its generalized gradient approximation (GGA). © 1996 John Wiley & Sons, Inc.     

Stereochemistry of the Robinson Anellation: Studies on the Mode of Formation of the Intermediate Hydroxy Ketones

The stereochemical outcome of the base-catalyzed cyclization of diketones 5 – 8 has been investigated under protic conditions (Scheme 3). The more stable trans-fused ketols are preferentially formed in kinetically controlled aldol reactions, when the incipient angular substituent R = H (6 → 10a ) or CN ( 7 → 11a , 8a → 12a ). For R = Me (as in 5 ), axial attack of the side-chain enolate double bond on the ring C?O group results in the rather selective formation of cis- 9b. It is assumed that these cyclizations are controlled by relative product stabilities (product-like transition state) and steric effects. The competition between fused (e.g. 9 ) and bridged ketol (e.g. 13 ) formation in these cyclizations is discussed. The cis-fused (‘steroid’) ketols were readily equilibrated with their trans-counterparts (9b ? 9a, 10b ? 10a, 11b ? 11a) under aprotic conditions (5 mol-% of LDA, THF, 0°), thus, allowing assessments of relative stabilities.     

Vorticity: Simplifying the analysis of the current density

The induced current density ( J ( r )) provides useful information about the electronic structure of molecules under a magnetic field ( B ). However, the analysis of its topology is cumbersome because of its vectorial nature. We show that its tropicity (direction of rotation) and its strength can be compressed in the triple product B ⋅ ∇ × J ( r ) (tp J ( r )) that is a scalar field. The topology of tp J ( r ) has clear similarities to the Laplacian of the electron density. Additionally, the topology of aromatic and antiaromatic compounds is notoriously different. The vorticity of J ( r ) is helpful to define the circulation of the current density, C, that contrary to other methods, can be easily defined for individual rings in polycyclic molecules. This allows tp J ( r ) to clearly reproduce the Clar's structure of polycyclic aromatic hydrocarbons. © 2019 Wiley Periodicals, Inc.     

Enzyme-Mediated Preparation of the Single Enantiomers of the Olfactory Active Components of the Woody Odorant Timberol®

Enantiomerically pure (3S)- 3a and - 3b , the olfactory active forms of 1-(2,2,6-trimethylcyclohexyl)hexan- 3-ol, components of the commercial woody odorant Timberol ^®, are obtained by lipase-PS-mediated enantioselective acetylation of the allylic alcohols 6 and 7 and of the saturated alcohol 3 . These materials, as mixtures of diastereoisomers, provided (3R)-configured transformation products. However, whereas in the conversion of 6 and 7 there is no diastereoselection, 3 provided the acetate of (1′S,3R,6′R)- 3c much more rapidly than that of the diastereoisomer (1′R,3R,6′S)- 3d (Scheme 3). Inversion of the configuration at C(3) of the side chain of the olfactory inactive (3R)-materials obtained as acetates in the enzymic treatment of 6 , 7 , and 3 also provided, eventually, the desired olfactory active (3S)-products.     

Effect of Cluster Deformations in the DLCA Modeling of the Sol-Gel Process

The diffusion limited cluster-cluster aggregation (DLCA) model is modified by including cluster deformations during aggregation, with a tuning flexibility parameter F. A three-dimensional computer simulation is presented, which starts from a collection of f-functional monomers randomly distributed in a cubic box with a volumic fraction c (concentration) and which uses the highly efficient bond fluctuation algorithm to describe the cluster deformations. It is shown that, for F 0, there exists a well defined threshold value of the volumic fraction below which the realization of all intra-aggregate bonding possibilities prevents the formation of a gelling network. For c > c _g , a true sol-gel transition occurs at a characteristic time t _g , after which an infinite cluster (which is self connected via the boundary conditions) appears. In contrast to DLCA, t _g does not increase as the box size increases. The transition at c _g is characterized by a divergence of the final clusters size for c<c _g and a divergence of the gel time for c>c _g . Several other numerical results are reported.     

New lipids from the soft corals of the Andaman Islands

Sphingolipids and glycolipids including previously unknown (2S,3S,4R)-1,3,4-trihydroxy-2-(2-(R)-hydroxyoctadecanoylamino)octadec-8E-ene, (2S,3R)-1,3-dihydroxy-2-octadecanoylamino-4E,8E-hexadecadiene, and (2-hydroxy-3-hexadecyloxypropyl)--L-fucopyranoside were isolated from soft corals collected on the shelf near the Andaman Islands (Indian Ocean). The structures of all compounds were established by spectroscopic methods and chemical analyses. The lipids possessed antibacterial activity against Bacillus subtilis, Bacillus pumilus, Escherichia coli, and Pseudomonas aeruginosa and antifungal activity against Aspergillus niger, Rhizopus oryzae, and Candida albicans.     

Comparison between the analysis of the asymptotic wavepacket and the associated flux for the calculation of kinetic-energy-releases function

The kinetic-energy-releases (KER) distribution function of the fragment is an important observable in the molecular dynamics. In theory, there are several different methods to calculate the KER distribution function or spectrum, which could be generally divided into two classes: One is based on the analysis of the asymptotic wavepacket (“projection method”) and the other is on the analysis of the associated flux (“flux method”). By taking the above-threshold dissociation of the HeH⁺ (v = 8) molecule as an example, we compared these two classes of methods. Based on evenly separated Fourier grid representation, the KER distribution calculated via the projection method F_Proj(E_k) is the same as the one calculated via the flux method F_Flux(E_k) . The relationship between F_Proj(E_k) and the distribution of the projection of the asymptotic wavepacket onto the energy eigenstates of the quasicontinuum, P_Proj(E_k) , and the relationship between F_Flux(E_k) and the distribution of the dissociation probability P_Flux(E_k) from the cumulation of the associated flux, are determined.     

Diazo Strategy for the Synthesis of Pyridazines: Pivotal Impact of the Configuration of the Diazo Precursor on the Process

Phosphazenes of vinyldiazocarbonyl compounds having cis stereochemistry of the functional groups on the vinyl bond readily produce pyridazines by a diaza‐Wittig process, whereas their counterparts with trans configuration remain intact under similar reaction conditions. Upon UV irradiation trans‐phosphazenes furnish pyridazines through a tandem trans‐to‐cis isomerization followed by intramolecular cyclization. At elevated temperatures trans‐(triphenyl)phosphazenes dissociate to give the initial vinyldiazo compounds, which produce pyrazoles in high yields. The first theoretical study on the mechanism of the diaza‐Wittig process by DFT calculations at the M06‐2X/6‐31G(d) level of theory suggest that for the cis‐phosphazenes a rapid tandem [2+2] cycloaddition/cycloelimination process with low energy barriers is preferred over trans isomers.     

On the representations of the rotation group

The matrices of the irreducible representations of the 3-dimensional rotation group are shown to be related to Krawtchouk's orthogonal polynomials of a discrete variable x = j – m', whose degrees are given by n = j + m. The relation follows directly from the recurrence formulas satisfied by the matrix elements and permits a concise development of the formal properties of the rotation matrices. In particular, an asymptotic relation for large j is developed that generalizes a formula first discussed for a special case by Wigner.     

Exact solutions of the rigid rotor in the electric field

We first present a new constraint condition on the confluent Heun function H_C(α, β, γ, δ, η;z) (β, γ ≥ 0, z ∈ [0, 1]) and then illustrate how to solve the rigid rotor in the electric field. We find its exact solutions unsolved previously through solving the Wronskian determinant. The present results compared with those by the perturbation methods are found to have a big difference for a large parameter a. We also present 2D and 3D probability density distributions by choosing different angular momentum quantum numbers l. We observe that the original eigenvalues with degeneracy (2 l + 1) are split into the (l + 1) state with approximate eigenvalues l(l + 1) for small a but large l.     

On the accuracy of the many-points local procedures

As until now proposed in the literature, in the local energy calculations we can distinguish “few-points” procedures, in which the number M of configurational points is strictly related to the number N of trial functions used, and statistical “many-points” procedures, in which the number M of points can be arbitrarily increased. In this paper we demonstrate that the energy errors resulting from a “many-points” calculation M points/N functions (M > N) can be connected in a simple way with the errors of the (^M_N) partial calculations N points/N functions. This suggests a possible approach for the problem of the choice of the configurational points to be introduced in the calculation, and leads to a simple interpretation of the numerical meaning of the error associated with the ordinary Ritz energy. Numerical examples on the hydrogen atom are reported.     

On the Effect of the Aglycon Structure of Three Aryl β-D-Galactosides on the Yield and the Regioselectivity of the Transglycolytic Synthesis of N-Acetyllactosamine

ABSTRACT

We examined the effect as donors of three aryl β-D-galactosides (i.e. p-nitrophenyl β-D-galactopyranoside, o-nitrophenyl β-D-galactopyranoside and phenyl β-D-galacto-pyranoside) on the regioselectivity and the yield of the synthesis of N-acetyllactosamine obtained from the transglycosylation reaction catalyzed by a crude preparation of β-D-galactosidase from Bacillus circulans at 25 °C, 37 °C and 55 °C, respectively. Using p-nitrophenyl β-D-galactopyranoside the reaction results were fully regiospecific at all the temperatures considered: the maximum molar yield (74%) was obtained at an incubation temperature of 55 °C. Using o-nitrophenyl β-D-galactopyranoside as the donor the reaction was still highly regioselective and the maximum molar yield (50%) was achieved at an incubation temperature also of 55 °C. Using phenyl β-D-galactopyranoside transglycolytic products appear only at an incubation temperature of 55 °C but at very low molar yield (about 14%) and lower regioselectivity.     

The photochemical reactions of the halogenated N-benzylanilines. Mechanism of the reactions

Several N-(2-halobenzyl)anilines and N-benzyl-2-haloanilines have been synthesized and their photochemical reactions studied. Upon irradiation, the aqueous acetonitrile solution of N-benzyl-2-chloroaniline was cyclized and reduced to give phenanthridine, 5,5′,6,6′-tetrahydro-6,6′-biphenanthridyl (THBP), N-ben-zylaniline, and bibenzyl. Similar products were produced in the photochemical reactions of other halo-genated N-benzylanilines, except iodo-substituted N-benzylanilines. No dimer (THBP) was produced from the iodo-substituted N-benzylanilines. Both singlet and triplet states are involved in the photochemical reactions of the haloarenes.     

Enumeration of the isomers of phenylenes

Summary The [h]phenylene C_6h H_2h+4 isomers are enumerated up toh=12. The numbers are compared with old and new data for C _n H₅ isomers of benzenoids, fluoranthenoids and biphenylenoids.

---

Anzahl möglicher Isomerer von Phenylenen

Zusammenfassung Die Anzahl der [h]Phenylen-Isomeren C_6h H_2h+4 wurde bish=12 ausgewertet. Die Zahlen wurden mit alten und neuen Daten für C _n H _s -Isomere von Benzenoiden, Fluoranthenoiden und Biphenyloiden verglichen.

     

Theoretical calculation of the steric effects of ortho substituents by the AM1 method

The AM1 calculation was done for ortho-substituted toluenes (o-X-C₆H₄-CH₃) and ortho-substituted tert-butylbenzenes (o-X-C₆H₄-t-Bu). The difference in the calculated heat of formation between o-X-C₆H₄-CH₃ and o-X-C₆H₄-t-Bu was used as a theoretical steric index for ortho-X. The correlation of this theoretical steric index with the empirical steric parameter sets such as our recently defined E_s(AMD) and the Taft–Kutter–Hansch (TKH) E_s was examined. In spite of the simplicity of the model system, the theoretical index was linear with the E_s(AMD) constant with a correlation coefficient of r = 0.972 for 17 substituents of various structures. Including the phenyl group, the correlation with the TKH E_s constant was r = 0.948. The theoretically calculated index was shown to serve as a measure of the ortho steric effect.