Adjacent Double Bond Research Articles

Assembling phthalaldehyde and o-aminochalcones by Pd(II) catalyzed tandem reaction for synthesizing isoindoloindonole fluorophores

One-pot synthesis of isoindoloindonoles having various auxochrome, from easily available starting materials phthalaldehyde and o-aminochalcone, involving palladium(II) acetate catalysis in acetic acid is reported. A mechanism based on the formation of 2-aryl-2H-isoindol-1-ol (22) intermediate is proposed for the formation of the tetracyclic core of isoindoloindonoles. The possible intramolecular cyclization via the direct participation of the carbonyl vs the adjacent αβ-conjugated double bond was evaluated. Thus, a detailed study on how the presence of electronically different groups at the β position of chalcones affects the outcome of the cyclization reaction and the photophysical properties of the resulting isoindoloindolones is presented here. Furthermore, the core structure was determined using NMR, mass and single-crystal X-ray diffraction analysis.

Macro peroxide initiators based on autoxidized unsaturated plant oils: Block/graft copolymer conjugates for nanotechnology and biomedical applications

AbstractThe autoxidation of unsaturated fatty acids and their esters is one of the most important reactions in food and biological systems. Autoxidation is a type of reaction between air oxygen and unsaturated plant oils. This reaction starts with a hydrogen abstraction on the methylene group adjacent double bond, leaving a radical onto the carbon atom. Molecular oxygen attacks this radical leading to produce peroxide and hydroperoxide derivatives of the oligomerized unsaturated plant oils. Because peroxide groups thermally cleave to produce free radicals, hydroperoxide derivatives of unsaturated plant oil oligomers can be used in the free radical polymerization of vinyl monomers leading to the related block/graft copolymers. The obtained copolymers combined with the biodegradable natural plant oil gain superior properties such as biodegradability and softness. In this review article, the in vitro autoxidation of well‐known unsaturated plant oils‐soybean oil, linseed oil, and castor oil and some related unsaturated fatty acids‐oleic acid, linoleic acid, and ricinoleic acid was carried out under atmospheric conditions with or without exposing white light. Because the autoxidized unsaturated oil/fatty acids contain peroxide/hydroperoxide groups (they are referred to as macro peroxide initiators) that they are used in the free radical polymerization of vinyl monomers to obtain block/graft copolymers. The improved polymerization conditions, characterization, and applications of the obtained products will be discussed.

Exploring of catalytic oxygen reduction reaction activity of lattice carbons of vanadium and niobium doped nitrogen codoped carbon nanotubes by density functional theory

AbstractThe oxygen electroreduction mechanism on the V‐ and Nb‐doped nitrogen‐codoped (6,6)armchair carbon nanotube with incorporated MN4 fragment has been studied using the ωB97XD and PBE density functional theory approaches. The metal center in MN4 fragment and the adjacent NCCN double bond (C2 site) of the support have been revealed as active centers. The metal active centers turned out to be irreversibly oxidized at the first step of ORR affording stable O*, 2O*, or O*HO* adsorbates depending on the applied electrode potential U, that makes them no longer active in ORR. Therefore, the C2 site comes at the forefront in ORR catalysis. Among the metal oxidized forms M(O)N4, M(O)(O)N4, and M(O)(OH)N4CNT, the C2 site of the latter turned out to be most active for 4e dissociative ORR. For both metals the last protonation/electron transfer step, HO* + H* → H2O, is the rate‐limiting step. The alternative hydrogen peroxide formation is not only thermodynamically less favorable but also kinetically slower than the 4e dissociative ORR route on the C2 site of model M(O)(OH)N4CNT catalyst.

Observation of Discrete Valence Tautomers in Crystalline Cyclopentadienyl Radicals.

Single crystal X-ray (sc XRD) analyses of three symmetrically substituted cyclopentadienyl radicals (1, 2, 5) containing sterically demanding aryl groups showed that they crystallize as discrete valence tautomers (Jahn-Teller distortion) in the solid state with the unpaired electron either located in the b1 orbital (type I, state 2B1), resulting in a localized radical with two adjacent double bonds, or the a2 orbital (type II, state 2A2), leading to an allyl-type radical. Their properties in solution were examined by EPR spectroscopy as well as cyclovoltammetry and UV/vis spectroscopy including two additional cyclopentadienyl radicals (1-5). The electronic nature of 1-5 was further investigated by quantum chemical calculations.

A stable diazoalkene

Organic Chemistry Modern organic chemistry has produced such a large array of intricately complex products that it is easy to forget the simple motifs that have eluded bulk synthesis. One such case is the diazoalkene, an unsaturated variant of the more common diazoalkanes. Consisting of three adjacent double bonds (C=C=N=N), this fragment is of particular interest as a precursor to reactive vinylidenes. Antoni et al. report the preparation of an N-heterocycle–substituted diazoalkene by oxidation of an olefinic precursor with nitrous oxide. The compound is stable in solid and solution states under inert atmosphere and reacts cleanly with isocyanides. Nat. Chem. 13 , 587 (2021).

Bent bond / antiperiplanar hypothesis and antiaromatic, aromatic and nonaromatic molecules

Abstract The stereochemical reactivities of monocyclic unsaturated compounds having 3–5 and 7–8 membered rings and of bicyclic pentalenes and heptalene can be rationalized through the bent bond/antiperiplanar hypothesis (BBAH) orbital model at the molecular level. This new orbital model considers unsaturations as Pauling τ bonds and that electron delocalization with adjacent pyramidal radical structures (derived from resonance structures) must strictly occur in antiperiplanar fashion. The BBAH shows that, contrary to aromatic (4n+2 Huckel) and nonaromatic molecules, antiaromatic molecules (4n Huckel) have adjacent double bonds that cannot conjugate through antiperiplanar electronic delocalization.

Asymmetric Total Synthesis of Phomarol

Asymmetric Total Synthesis of Phomarol

One-Step Synthesis of Novel Renewable Vegetable Oil-Based Acrylate Prepolymers and Their Application in UV-Curable Coatings.

With the rapid development of social economy, problems such as volatile organic compound (VOC) pollution and the excessive consumption of global petroleum resources have become increasingly prominent. People are beginning to realize that these problems not only affect the ecological environment, but also hinder the development of the organic polymer material industry based on raw fossil materials. Therefore, the modification and application of bio-based materials are of theoretical and practical significance. In this study, a series of vegetable oil-based acrylate prepolymers were synthesized by one-step acrylation using palm oil, olive oil, peanut oil, rapeseed oil, corn oil, canola oil, and grapeseed oil as raw materials, and the effect of different double bond contents on the product structure and grafting rate was investigated. Furthermore, the as-prepared vegetable oil-based acrylate prepolymers, polyurethane acrylate (PUA-2665), trimethylolpropane triacrylate (TMPTA), and photoinitiator (PI-1173) were mixed thoroughly to prepare ultraviolet (UV)-curable films. The effect of different grafting numbers on the properties of these films was investigated. The results showed that as the degree of unsaturation increased, the acrylate grafting number and the cross-linking density increased, although the acrylation (grafting reaction) rate decreased. The reason was mainly because increasing the double bond content could accelerate the reaction rate, while the grafted acrylic groups had a steric hindrance effect to prevent the adjacent double bonds from participating in the reaction. Furthermore, the increase in grafting number brought about the increase in the structural functionality of prepolymers and the cross-linking density of cured films, which led to the enhancement in the thermal (glass transition temperature) and mechanical (tensile strength, Young’s modulus) properties of the cured films.

Carbon Tunneling in the Automerization of Cyclo[18]carbon.

Cyclo[18]carbon (C18 ), a recently synthesized carbon allotrope, was found to have a polyynic ground-state structure with D9h symmetry and formally alternating single and triple bonds. Yet, under less influencing experimental conditions this molecule might undergo an automerization reaction between its two degenerate geometries through a cumulenic (non-alternating, adjacent double bonds) D18h transition state. Herein, we discuss the role of quantum mechanical tunneling (QMT) in this degenerate reaction. Our computations predict that at the experimental temperature (5 K) the reaction in the gas phase is completely driven by an extremely rapid heavy atom tunneling (k=2.1×108 s-1 ). Even when approaching room temperature, the QMT rate is still an order of magnitude faster than the semi-classical one. We propose an experimental test to support our prediction, by measuring a characteristic tunneling energy splitting within the radio wave region. Additionally, we examine the role of QMT in other hypothetical C4n+2 carbon clusters.

High Molecular Weight Polyester Obtained by Polymerization of Dimethylketene Using Metallocene Initiators: A Step toward Ziegler-Natta Supporting Application in Non-Olefin Systems.

In this report, highly active metallocene initiators are used for the polymerization of a ketene monomer, dimethylketene, which typically contains two adjacent double bonds (R2 CCO). By using the methylzirconocene methyltriarylborate complex (Cp2 ZrMe+ MeB(C6 F5 )3 - ) as the activation system, associated with the possible cleavage of CC and CO bonds in ketene monomers, a structure-specific and high-molecular-weight polyester ( > 300 000 g mol-1 ) can be afforded. The resulting polyester structure, comprehensively characterized by NMR, indicates a significant reactive selectivity of the "bent-sandwich" cationic site Cp2 ZrMe+ . It reveals that the positively charged zirconium (Zr+ ) prefers to coordinate with a negatively charged oxygen (O- ) when it is already bonded to the carbon, while a negatively charged carbon (C- ) will be assigned in priority if the oxygen-zirconium bond exists. This report allows for broadening the application field of metallocene initiators in non-olefin reactions and deepening our insight into the mechanism of the living insertion/Ziegler-Natta polymerization.

Different mutual positions of double bonds in open carbon chains and corresponding information from magnetically induced current densities

AbstractMagnetically induced current densities have been extensively utilized to investigate aromaticity. However, an applied external magnetic field induces a current in all chemical bonds. The present work investigates the values and patterns of magnetically induced current densities in open hydrocarbon chains containing two or more CC double bonds, considering the three possibilities for the mutual positions of the double bonds (conjugated, isolated, and consecutive) and comparing the corresponding current patterns. The patterns for chains containing three conjugated double bonds are also compared with the patterns in the aromatic benzene ring. The study highlights different current patterns for the three categories of double‐bonds arrangements. The differences can be interpreted in terms of presence or absence of electron delocalization (present only in the case of conjugated double bonds) and, for consecutive double bonds, also in terms of the mutual perpendicularity of the π orbitals of adjacent double bonds.

Redox-Active Cobalt(II/III) Metal-Organic Framework for Selective Oxidation of Cyclohexene.

We report herein a new cobalt(II/III) mixed-valence metal-organic framework formulated as [CoIICo2III(μ3-O)(bdc)3(tpt)]·guest 1, where bdc = benzene-1,4-dicarboxylate and tpt = 2,4,6-tri(4-pyridinyl)-1,3,5-triazine, which can be used as a redox-active heterogeneous catalyst for selective oxidation of cyclohexene on the allylic position without destroying the adjacent double bond. Two oxidants were chosen to demonstrate this result. For using tert-butyl hydroperoxide, the conversion rate is 63% and only allylic oxidation products ( tert-butyl-2-cyclohexenyl-1-peroxide, 86%; 2-cyclohexen-1-one, 14%) are found, whereas if using O2 as oxidant, a total conversion of 38% is achieved and also only the allylic oxidation products (cyclohexenyl hydroperoxide, 72%; 2-cyclohexen-1-one, 20%; and cyclohex-2-en-1-ol, 8%) are found. The absence of any adduct on the double bond may be due to the unique radical chain mechanism triggered by the mixed-valent [CoIICo2III(μ3-O)] centers.

(Invited) Structural Identification of 19 Purified Isomers of Opv Acceptor Material Bis[60]PCBM

The molecular structures of 19 purified isomers of bis-phenyl-C62-butyric acid methyl ester (“bis[60]PCBM”) were identified by a combination of 13C NMR and UV-Vis absorption spectroscopy, and HPLC retention time analysis. The 13C NMR spectra indicated the symmetry of each isomer. It also showed that all 19 isomers are dicyclopropa-fullerenes (none are homo-fullerenes). This is because the fullerene bridgehead for both addends are sp 3 hybridized; resonating between 75 and 85 ppm. According to UV-Vis spectroscopy, the 19 isomers were classified into 7 groups - each corresponding to one of the 7 bond types identified by Hirsch and co-workers (trans-1, trans-2, trans-3, trans-4, e, cis-3, cis-2). All 58 nominal molecular structures of Bis[60]PCBM were accounted for by isolating the first addend as bridging fullerenes carbon 1 and 9 by default, after which the 2nd addend may to one of the 29 remaining double bonds on C60 with two orientations relative to that of the 1st addend. However, symmetry reduced this number to 36 physically distinguishable isomers. Many of these isomers have enantiomers, and hence cannot be spectroscopically distinguished; which reduces the number of effective isomers to 22. If these, 3 are not expected to form owing to steric hindrance because each of these three isomers involve the cis-1 bond whereby the bulky addends would be attached to two adjacent double bonds on the same 6-membered ring on C60. There were 7 isomers with C1 molecular point group symmetry, 4 with CS, 6 with C2, 1 with C2v and 1 with C2h symmetry. The C2h, C2v, and all 5 non-equatorial C1 molecular structures were unambiguously assigned to their respective HPLC fractions. For the other 12 isomers, the 13C NMR and UV-Vis spectra placed them in 6 groups of two same-symmetry isomers. Based on the widely spaced HPLC retention times of the two isomers within each of these 6 groups, and the empirical inverse correlation between retention time and addend spacing, each molecular structure was assigned to its corresponding HPLC fraction. The information presented will enable those who follow and produce photovoltaic devices based purified isomers to know which specific isomer is being employed in their devices, develop a deeper understanding of morphological order/disorder within the acceptor phase, and thereby draw meaningful conclusions on why some isomers perform better than others.

Analytical nuclear derivatives for the parametric two-electron reduced density matrix method

Efficient and accurate nuclear gradients are essential to performing molecular optimizations. Here for the first time we present analytical nuclear gradients for the parametric two-electron reduced-density-matrix method (p2-RDM), which uses the 2-RDM as the primary variable in calculations in lieu of the many-electron wavefunction. While numerical gradients require six energy evaluations for each atom, analytical gradients require only a single calculation for each geometry sampled. We present benchmark p2-RDM geometry optimizations that show analytical gradients reduce CPU times by as much as 80%, even for small molecules. We also use p2-RDM to evaluate the bond length alternation (BLA), or the difference in length between adjacent single and double bonds, of trans-polyacetylene (PA). We find that the BLA in the extrapolated limit to be 0.080Å, in agreement with experiment and closely mirroring the prediction of the more expensive coupled-cluster with single and double excitations with perturbative triples (CCSD(T)).

Valence Bond Theory Reveals Hidden Delocalized Diradical Character of Polyenes.

The nature of the electronic-structure of polyenes, their delocalization features, and potential diradicaloid characters constitute a fundamental problem in chemistry. To address this problem, we used valence bond self-consistent field (VBSCF) calculations and modeling of polyenes, C2nH2n+2 (n = 2-10). The theoretical treatment shows that starting with n = 5, the polyene's wave function is mainly a shifting 1,4-diradicaloid, a character that increases as the chain length increases, while the contribution of the fundamental Lewis structure with alternating double and single bonds (1) decays quite fast and becomes minor relative to the diradicaloid pack. We show how, nevertheless, it is this wave function that predicts that polyenes will still exhibit alternating short/long CC bonds like the fundamental structure 1. Furthermore, despite the decay of the VB contribution of 1, it remains the single structure with the largest weight among all the individual structures. The mixing of all the 1,4-diradicaloid structures into 1 follows perturbation theory rules, with the result that the delocalization energy due to this mixing is additive and behaves as a linear function of the number of the double bonds, ΔEdel = -6.9 × n (kcal mol-1). The VB modeling shows that while the conjugation stabilizes structure 1, this stabilization energy is energetically overridden by the Pauli repulsion between two adjacent double bonds. Nevertheless, unsubstituted polyenes remain planar; this observation is addressed. Potential manifestations of the diradicaloid nature of polyenes are discussed, and it is concluded that the diradicaloid character is clearly not a well-defined physical property as in real diradicals. Thus, we went full circle to realize that our philosophical question may not be strictly resolved. The localized/delocalized properties of polyenes seem to define a "chemical duality principle". This duality of molecular wave functions is a ubiquitous beguiling phenomenon.

Getting the chemistry right: protonation, tautomers and the importance of H atoms in biological chemistry.

There are more H atoms than any other type of atom in an X-ray crystal structure of a protein-ligand complex, but as H atoms only have one electron they diffract X-rays weakly and are `hard to see'. The positions of many H atoms can be inferred by our chemical knowledge, and such H atoms can be added with confidence in `riding positions'. For some chemical groups, however, there is more ambiguity over the possible hydrogen placements, for example hydroxyls and groups that can exist in multiple protonation states or tautomeric forms. This ambiguity is far from rare, since about 25% of drugs have more than one tautomeric form. This paper focuses on the most common, `prototropic', tautomers, which are isomers that readily interconvert by the exchange of an H atom accompanied by the switch of a single and an adjacent double bond. Hydrogen-exchange rates and different protonation states of compounds (e.g. buffers) are also briefly discussed. The difference in heavy (non-H) atom positions between two tautomers can be small, and careful refinement of all possible tautomers may single out the likely bound ligand tautomer. Experimental methods to determine H-atom positions, such as neutron crystallography, are often technically challenging. Therefore, chemical knowledge and computational approaches are frequently used in conjugation with experimental data to deduce the bound tautomer state. Proton movement is a key feature of many enzymatic reactions, so understanding the orchestration of hydrogen/proton motion is of critical importance to biological chemistry. For example, structural studies have suggested that, just as a chemist may use heat, some enzymes use directional movement to protonate specific O atoms on phosphates to catalyse phosphotransferase reactions. To inhibit `wriggly' enzymes that use movement to effect catalysis, it may be advantageous to have inhibitors that can maintain favourable contacts by adopting different tautomers as the enzyme `wriggles'.

Strongly localized approaches for delocalized systems. I. Ground state of linear polyenes

When approaching the theoretical description of the electronic structure of a molecule, instead of starting the construction of the electronic wave function from the self-consistent field single determinant, one may use a strongly localized determinant, corresponding to the Lewis picture of the molecule. Following this approach, the delocalization and the correlation effects are clearly identified and they can be treated simultaneously. This analysis, applied to the study of the ground state of π-conjugated systems, in particular to all-trans linear polyenes, shows the short-range character of the delocalization, essentially taking place between adjacent double bonds, and of the valence correlation energy, mainly coming from intra-double bond double excitations. This suggests that these systems can be described with a very limited model space, reduced to the corresponding excitations, the size of which scales linearly with the dimension of the system. Of course the effect of other excitations and of multiple excitations has to be taken into account at least in a perturbation scheme. The numerical studies on the first terms of the polyenes series show that the so-obtained energies are very close to those of the full π Complete Active Space Self-Consistent Field treatment. Moreover, one can correctly reproduce the dependence of the energy on the bond length alternation, thus showing the origin of the differences observed in these systems for the HF and CASSCF equilibrium geometries.

Unusually large scalar coupling between geminal protons in a saturated pyrimidine

AbstractAn unusually large geminal coupling has been observed in a stereochemically rigid system that permits a favorable coupling alignment between the methylene protons and an adjacent carbon‐carbon double bond. Such couplings have been found to depend on both the alignment of a line connecting the geminal hydrogens and the nodal plane of the adjacent double bond, and the orientation of lone‐pair electrons on adjacent heteroatoms. Electron withdrawal from symmetrical bonding orbitals results in more slightly positive geminal coupling constants while that from antisymmetrical bonding orbitals produces more negative coupling constants, which has been found to be very large in certain rigid systems.

Development of cooler running PCR tire tread using SBR–ENR–nano clay composite

In this investigation, the emphasis is given to the partial replacement of carbon black by an optimized level of Cloisite 15A, an organoclay in a typical styrene-butadiene rubber (SBR) based passenger car tire tread compound. The effect of epoxidized natural rubber with 50 % epoxidation (ENR 50) on the properties of organoclay-SBR composite was also studied. Curing studies shows that both ENR 50 and nanoclay decreases the scorch time and cure time due to the activation of an adjacent double bond by the presence of epoxide group in the ENR and the amine groups present in the organic modifier in the nanoclay structure. The incorporation of ENR showed better dispersion and exfoliation of nanoclay in the rubber matrix. Synergistic reinforcement effect of high abrasion furnace carbon black (HAF/N330) on the mechanical properties, dynamic mechanical properties, heat build up and abrasion resistance in the SBR–ENR–clay nanocomposites having the optimized clay level was investigated. SBR–ENR–carbon black hybrids with 25 phr N330 and 6 phr nanoclay have shown better reinforcement, significantly lower heat generation, comparable/similar rolling resistance (indicated by tan δ at 60 °C) and wet skid resistance with that of conventional SBR–carbon black (40 phr N330) loaded composites.

Lipids and Polysaccharides from Seeds of Stachys hissarica

The compositions of lipids and fatty acids and the carbohydrate complex from seeds of the endemic plant Stachys hissarica were established. Neutral lipids were dominated by fatty acids 18:2ω6 and 18:1. The principal acid in glyco- and phospholipids was 16:0. Fatty acids of neutral lipids contained trace quantities of 18:2 (5,6) laballenic acid with adjacent double bonds. The carbohydrate complex from S. hissarica seeds was studied and found to include water-soluble polysaccharides, pectinic substances, and hemicellulose. Their physicochemical properties were presented.