A catalogue of growth transformations of fullerene polyhedra

Carbon insertion or extrusion mechanisms transforming one fullerene to another are presented as patch replacements on the fullerene surface. A systematic catalogue is constructed for the topologically distinct local insertion/extrusion transformations of fullerenes, classified by patch boundary and pentagon content. All pairs of patches with the same boundary but different numbers of atoms, i.e., growth patches, containing up to five pentagons, with an upper limit for the boundary length that depends on the number of pentagons, are listed. New transformations and infinite series of transformations are identified.     

New isomerization operations for fullerene graphs

The problem of topological isomerization operations for fullerenes is considered. Two basic classes of isomerization transformations admissible for fullerene graphs are proposed: rotation and mirror reflection of a chosen part of fullerene graph. Pyracylene and generalized Stone-Wales rearrangements are only the specific cases of extended isomerization operations for the fullerene graphs.     

Kost-Sagitullin Rearrangement and Other Isomerization Recyclizations of Pyrimidines. (Review)

Data on the isomerization recyclizations of pyrimidines, particularly the Kost-Sagitullin and other transformations accompanied by substitution of an endocyclic atom in pyrimidine by an extracyclic nitrogen or carbon atom (N-N, N-C, or C-C recyclizations), are summarized and analyzed. Data from research on the Kost-Sagitullin and certain other isomerization transformations of pyrimidines at the Institute of Organic Chemistry, National Academy of Sciences of the Republic of Armenia, in recent years are presented. In memory of Aleksei Nikolaevich Kost — a distinguished scientist, a warmhearted person, and a teacher. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1445–1480, October, 2005.     

Homolytic liquid-phase reactions of 1,3-dioxacyclanes (review)

The literature data on the liquid-phase homolytic isomerization, addition, substitution, and oxidation reactions of 1,3-dioxacyclanes are examined. The problems involved in the formation, stabilities, kinetics, and mechanisms of the transformations of free radicals in a series of cyclic acetals are discussed. Possibilities for the application of the homolytic transformations of 1,3-dioxacyclanes in organic synthesis are demonstrated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1011–1025, August, 1977.     

Numbers of faces in disordered patches

It has been shown that the boundary structure of patches with all faces of the same size k, all interior vertices of the same degree m and all boundary vertices of degree at most m determines the number of faces of the patch (Brinkmann et al., Graphs and discovery, 2005; Guo et al., Discrete Appl Math 118(3):209–222, 2002). In case of at least two defective faces, that is faces with degree k′ ≠ k, it is well known that this is not the case. The most famous example for this is the Endo–Kroto C ₂-insertion (Endo and Kroto, J Phys Chem 96:6941–6944, 1992). Patches with alimited amount of disorder are especially interesting for the case k = 6, m = 3 and k′ = 5. This case corresponds to polycyclic hydrocarbons with a limited number of pentagons and to subgraphs of fullerenes. The last open question was the case of exactly one defective face or vertex. In this paper we generalize the results of Brinkmann et al. (2005) and Guo et al. (2002) and in some cases corresponding to Euclidean lattices also deal with patches that have vertices of degree larger than m on the boundary, have sequences of degrees on the boundary that are identical only modulo m and have vertex and face degrees in the interior that are multiples of m, resp. k. Furthermore we prove that in case of at most one defective face with a degree that is not a multiple of k the number of faces of a patch is determined by the boundary. This result implies that fullerenes cannot grow by replacing patches of a restricted size.     

Photochemistry of quaternary salts of aromatic heterocycles and some of their mesoionic derivatives (Review)

The photochemical methods far the synthesis of quaternary salts of aromatic heterocycles, their photochemical reduction reactions, photoreactions with water, some photochemical transformations that proceed without a change in the charged heterocycle, and photoreactions involving valence isomerization and fragmentation of the mesoionic derivatives are examined.     

Strain Release of Fused Pentagons in Fullerene Cages by Chemical Functionalization

According to the isolated pentagon rule (IPR), for stable fullerenes, the 12 pentagons should be isolated from one another by hexagons, otherwise the fused pentagons will result in an increase in the local steric strain of the fullerene cage. However, the successful isolation of more than 100 endohedral and exohedral fullerenes containing fused pentagons over the past 20 years has shown that strain release of fused pentagons in fullerene cages is feasible. Herein, we present a general overview on fused‐pentagon‐containing (i.e. non‐IPR) fullerenes through an exhaustive review of all the types of fused‐pentagon‐containing fullerenes reported to date. We clarify how the strain of fused pentagons can be released in different manners, and provide an in‐depth understanding of the role of fused pentagons in the stability, electronic properties, and chemical reactivity of fullerene cages.     

Regioselective ring opening and isomerization reactions of 3,4-epoxyesters catalyzed by boron trifluoride

Efficient ring opening of 3,4-epoxyesters with alcohols to produce 4-alkoxy-3-hydroxyesters and their isomerization into 4-ketoesters using boron trifluoride as the catalyst are presented. Both transformations are simple and efficient methods for the synthesis of the above named synthetically useful compounds.     

Thermal isomerization of 5-methoxy-3-arylisoxazoles to methyl 3-aryl-2H-azirine-2-carboxylates

The thermal isomerization of 5-methoxy-3-arylisoxazoles to methyl 3-aryl-2H-azirine-2-carboxylates was subjected to a kinetic study. A correlation between the isomerization rate constants and the ⁺ constants of the substituents in the aromatic ring is observed. The enthalpies of formation of a number of isoxazoles and 2H-azirines were calculated. The effect of the nature of the substituents on the mutual isomerization of isoxazoles and azirines is discussed. The results make it possible to refute the approved and previously proposed diradical mechanism for the isomeric transformations and are in agreement with a nitrene mechanism for the formation of azirines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1053–1056, August, 1978.     

The facile preparation of alkenyl metathesis synthons

We report synthetic methodology allowing the preparation of any length alkenyl halide from inexpensive starting reagents. Standard organic transformations were used to prepare straight chain α-olefin halides in excellent overall yields with no detectable olefin isomerization and full recovery of any unreacted starting material. Reported transformations can be used for the selective incorporation of pure α-olefin metathesis sites in highly functionalized molecules.     

Enolization in the radiolysis of acetone

Radiolytic transformations in acetone proceed with the direct participation of its enol tautomer and its derivatives formed as a result of isomerization of excited molecules and ions, as well as chemical reactions catalyzed by acidic products of radiolysis.     

Pentaheptite modifications of the graphite sheet

Pentaheptites (three-coordinate tilings of the plane by pentagons and heptagons only) are classified under the chemically motivated restriction that all pentagons occur in isolated pairs and all heptagons have three heptagonal neighbors. They span a continuum between the two lattices exemplified by the boron nets in ThMoB4 (cmm) and YCrB4 (pgg), in analogy with the crossover from cubic-close-packed to hexagonal-close-packed packings in 3D. Symmetries realizable for these pentaheptite layers are three strip groups (periodic in one dimension), p1a1, p112, and p111, and five Fedorov groups (periodic in two dimensions), cmm, pgg, pg, p2, and p1. All can be constructed by simultaneous rotation of the central bonds of pyrene tilings of the graphite sheet. The unique lattice of cmm symmetry corresponds to the previously proposed pentaheptite carbon metal. Analogous pentagon-heptagon tilings on other surfaces including the torus, Klein bottle, and cylinder, face-regular tilings of pentagons and b-gons, and a full characterization of tilings involving isolated pairs and/or triples of pentagons are presented. The Kelvin paradigm of a continuum of structures arising from propagation of two original motifs has many potential applications in 2D and 3D.     

The photoreaction mechanism in the bacterial blue light receptor BLUF according to metadynamics modeling

The mechanism of chemical transformations in the blue light photoreceptor domains (BLUF) implies the isomerization of the glutamine side chain. The Helmholtz energy profiles for the side-chain isomerization of the tautomeric form of glutamine in the BLUF domain of the bacterial protein AppA were calculated using metadynamics and the potentials that were obtained using quantum mechanics-molecular mechanics approximation (QM/MM).     

Computed structures of two known Yb@C74 isomers

Six isomers of Yb@C74 are considered, namely one cage with isolated pentagons, three isomers with a pentagon-pentagon junction, two structures with one pentagon-pentagon pair, and one heptagon. The computations based on the Gibbs energy point out the endohedral derived from the only C74 cage with the isolated pentagons and from a cage with one pentagon-pentagon junction as the major and minor observed isomer, respectively. Temperatures giving the best agreement with the experimental production ratio are evaluated.     

Hydrous Pyrolysis of Methylphenanthrenes – Degradation and Isomerization

A simulation of the chemical transformations of methylphenanthrenes in sediment was performed using hydrous pyrolysis technique. The results indicate that isomerization is not the primary cause of the change in the MPI₁ index. Rather, the degradation reaction of methylphenanthrenes to phenanthrene is one of the most likely causes reversing the trend of the MPI₁ index with increasing the heating temperature. An unusual isomerization between 2‐methylphenanthrene and 9‐methylphenanthrene was also observed during the course of heating experiments. A plausible mechanism involving [1,5]‐methyl shift was proposed for this isomerization reaction.     

Table of periodic properties of fullerenes based on structural parameters

The periodic table (PT) of the elements suggests that hydrogen could be the origin of everything else. The construction principle is an evolutionary process that is formally similar to those of Darwin and Oparin. The Kekulé structure count and permanence of the adjacency matrix of fullerenes are related to structural parameters involving the presence of contiguous pentagons p, q and r. Let p be the number of edges common to two pentagons, q the number of vertices common to three pentagons, and r the number of pairs of nonadjacent pentagon edges shared between two other pentagons. Principal component analysis (PCA) of the structural parameters and cluster analysis (CA) of the fullerenes permit classifying them and agree. A PT of the fullerenes is built based on the structural parameters, PCA and CA. The periodic law does not have the rank of the laws of physics. (1) The properties of the fullerenes are not repeated; only, and perhaps, their chemical character. (2) The order relationships are repeated, although with exceptions. The proposed statement is the following: The relationships that any fullerene p has with its neighbor p + 1 are approximately repeated for each period.     

Reference-Quality Free Energy Barriers in Catalysis from Machine Learning Thermodynamic Perturbation Theory

For the first time, we report calculations of the free energies of activation of cracking and isomerization reactions of alkenes that combine several different electronic structure methods with molecular dynamics simulations. We demonstrate that the use of a high level of theory (here Random Phase Approximation—RPA) is necessary to bridge the gap between experimental and computed values. These transformations, catalyzed by zeolites and proceeding via cationic intermediates and transition states, are building blocks of many chemical transformations for valorization of long chain paraffins originating, e.g., from plastic waste, vegetable oils, Fischer–Tropsch waxes or crude oils. Compared with the free energy barriers computed at the PBE+D2 production level of theory via constrained ab initio molecular dynamics, the barriers computed at the RPA level by the application of Machine Learning thermodynamic Perturbation Theory (MLPT) show a significant decrease for isomerization reaction and an increase of a similar magnitude for cracking, yielding an unprecedented agreement with the results obtained by experiments and kinetic modeling.     

Stereoselective Synthesis of Vinylboronates by Rh‐Catalyzed Borylation of Stereoisomeric Mixtures

The stereoselective preparation of vinylboronates via rhodium‐catalyzed borylation of E/Z mixtures of vinyl actetates is described, and this method was also extended to synthesis of vinyldiboronates. These transformations feature high functional group compatibility and mild reaction conditions. Control experiments support a mechanism that involved a Rh‐catalyzed borylation‐isomerization sequence. The isomerization of (Z)‐vinylboronates to (E)‐isomers was also demonstrated.     

Transformations of p-menthadienes under the action of potassium tert-butanolate in dimethyl sulfoxide

The products of the transformation of α- and γ-terpinenes, terpinolene, (+)-transisolimonene, and (+)-limonene under the action of potassium tert-butanolate in dimethyl sulfoxide contained — in addition to the α- and γ-terpinenes, isoterpinolene, p-mentha-3,8-diene and p-cymene found previously — terpinolene, α- and β-phellandrenes, p-mentha-2,4-diene (in a total amount of 1–3%), and polymers. Under these conditions, limonene is racemized. The primary products of the isomerization reaction have been identified. A supplementary scheme for the isomerization transformations of p-menthadienes is presented.