Symmetric Trans Research Articles

Carbonyl Oxide Stabilization from Trans Alkene and Terpene Ozonolysis.

The pressure dependence of carbonyl oxide (Criegee intermediate) stabilization can be measured via H2SO4 detection using chemical ionization mass spectrometry. By selectively scavenging OH radicals in a flow reactor containing an alkene, O3, and SO2, we measure an H2SO4 ratio related to the Criegee intermediate stabilization, and by performing experiments at multiple pressures, we constrain the pressure dependence of the stabilization. Here, we present results from a set of monoterpenes as well as isoprene, along with previously published results from tetramethylethylene and a sequence of symmetrical trans alkenes. We are able to reproduce the observations with a physically sensible set of parameters related to standard pressure falloff functions, providing both a consistent picture of the reaction dynamics and a method to describe the pressure stabilization following ozonolysis of all alkenes under a wide range of atmospheric conditions.

Models of molecular photocatalysts for water oxidation: Strategies for conjugating the Ru(bda) fragment (bda = 2,2′-bipyridine-6,6′-dicarboxylate) to porphyrin photosensitizers

Model dyads, in which the Ru(bda) water oxidation catalyst (WOC) is connected to a porphyrin, were prepared following two different modular strategies: i) the direct linkage approach, in which porphyrins bearing peripheral pyridyl rings are bound to the {Ru(bda)} fragment as axial ligands, and ii) the metal-containing ligand approach, in which symmetrical trans-[Ru(bda)(L)2] or unsymmetrical trans-[Ru(bda)(L)(pic)] compounds (L = bifunctional pyridyl linker), are axially bound to metalloporphyrins. Both synthetic strategies are modular and thus rather flexible in nature. As proofs of principle, the following Ru(bda) – porphyrin dyads are described: trans-[Ru(bda)(4′-MPyP)2] (2, 4′-MPyP = 5-(4′-pyridyl)-10,15,20-phenylporphyrin), and the sandwich compounds [trans-Ru(bda)(4,4′-bpy)2{Ru(CO)(TPP)}2] (5) and [trans-Ru(bda)(4,4′-bpy)2(6Zn)]2 (7), where 6Zn is the porphyrin metallacycle [trans,cis,cis-RuCl2(CO)2(Zn·4′-cisDPyP)]2 (4′-cisDPyP = 5,10-(4′-pyridyl)-15,20-(phenyl)-porphyrin.

Synthesis of Dimeric Steroid Trioxabispiroacetals Scaffolds by Gold(I)‐Catalyzed Hydroalkoxylation–Hydration of Diynediols

Five novel dimers in which the steroid cores are bridged by a 6,5,6‐trioxabispiroacetal moiety were synthesized by gold(I)‐catalyzed hydroalkoxylation–hydration of steroid diynediols. The double spiroacetalization proceeded with excellent yield and produced almost exclusively the C2 symmetrical trans diastereomer. A small amount of the cis unsymmetrical diastereomer was isolated only in one case. Density Functional Theory calculations were used to further analyze and justify the population of the diastereomers. Characterization of the obtained dimers was based on combined 1D and 2D NMR techniques. X‐ray diffraction of one of the obtained dimers corroborated the anticipated V‐shaped structure and provided additional structural insights on the crystal network. Unexpectedly, the crystalline array showed interconnected voids, resulting in channels that make this new class of steroid dimers suitable candidates for the development of applications on solid state supramolecular chemistry.

Cover Feature: Unusual C2h‐Symmetric trans‐1‐(Bis‐pyrrolidine)‐tetra‐malonate Hexa‐Adducts of C60: The Unexpected Regio‐ and Stereocontrol Mediated by Malonate–Pyrrolidine Interaction (Chem. Eur. J. 63/2017)

Cover Feature: Unusual <i>C</i>_2h‐Symmetric <i>trans‐</i>1‐(Bis‐pyrrolidine)‐tetra‐malonate Hexa‐Adducts of C₆₀: The Unexpected Regio‐ and Stereocontrol Mediated by Malonate–Pyrrolidine Interaction (Chem. Eur. J. 63/2017)

Exploring the structural and conformational properties of dioxygen dihalides (halogen = F, Cl, Br)

The structural and conformational properties of dioxygen difluoride (1), dioxygen dichloride (2), and dioxygen dibromide (3) have been investigated by means of the hybrid density functional theory (B3LYP) and the hybrid meta exchange-correlation functional (M06-2X) with the aug-cc-pVQZ, aug-cc-pVTZ, cc-pVTZ, and 6-311++G** basis sets and natural bond orbital interpretation. The results obtained showed that the rotation at the O–O bond by passing from the plane symmetrical trans-(C2h) (or cis-(C2v)) form leads to the O–F bonds breaking. The natural bond order analysis revealed that the O–O bonds in the C2h and C2v forms of compound 1 possess double bond characters and the small bond orders between the oxygen and fluorine atoms results from the strong electron delocalization between the lone pairs of the fluorine atoms (LP4F) and the antibonding orbitals of the adjacent O–O double bond (π*O–O). The lengthening and shortening of the O–F and O–O bonds, respectively, in the trans-(C2h) or cis-(C2v) forms of compound 1 can be interpreted by the decrease of the bonding interactions between the fluorine and oxygen orbitals. The profiles of the orbital amplitudes (or electron densities) of O–O and O–F bonds in the C2h and C2v forms of compound 1 revealed that there are strong electronic repulsions between the πO–O and the lone pairs of oxygen atoms with the lone pairs of fluorine atoms, leading to the dissociation of O–F bonds. It is worth noting that there are strong hyperconjugative interactions between LP2O and the antibonding orbitals of adjacent O–F bonds (σ*O–F) in the skew (C2) form of compound 1, leading to the decrease of the O–O bond length and the increase of the F–O bond length by increasing the πO-O bonding and the σ*O–F antibonding orbital occupations. The increase of the electron delocalization from LP3F to σ*O–O with the decrease of the σ*O–O–σO–O energy gap (results from the increase of the O–O bond length) justifies the similarity between the adiabatic O–O bond dissociation energies in compound 1 and HOOH. The electron delocaizations from LP2O2 to σ*O3–X (X = F (1), Cl (2), Br (3)) decrease drastically from the skew ground state (C2) forms of compound 1 to compound 2 but increase slightly from compound 2 to compound 3, causing the significant increase of the O–O bond length ongoing from compound 1 to compound 2 and the slight decrease from compound 2 to compound 3. Effectively, the conformational properties of compounds 1–3 can be interpreted with the principle of maximum softness.

Theoretic study of DNA base guanine and adenine and protein residues’ binding mode of the trans geometries of new antitumor non-classical platinum complexes containing pyridine and picoline ligand

The first and second substitution reactions of five activated trans platinum (II) compounds with DNA purine bases and protein residues are explored here. The free energy barriers relative to the first substitutions of these compounds are 19.5/22.9 kcal/mol (trans-[PtCl2(NH3)pyridine], (1), 16.5/14.6 kcal/mol (trans-[PtCl2(pyridine)2], (2), 18.3/18.0 kcal/mol (trans-[PtCl2(NH3)(2-picoline)], (3), 16.4/18.4 kcal/mol(trans-[PtCl2(NH3)(3-picoline)], (4), and 17.5/18.7 kcal/mol (trans-[PtCl2(NH3)(4-picoline)], (5), starting from trans-Pt-chloroaqua to trans-Pt-G/A monoadduct, while 22.5/24.8 kcal/mol(1), 18.5/23.9 kcal/mol(2), 24.3/24.9 kcal/mol(3), 23.3/24.3 kcal/mol(4), and 18.7/24.0 kcal/mol(5) are observed for trans-Pt-diaqua → trans-Pt-G/A monoadduct. In the second substitutions, reaction barriers for (G-Pt-G) head-to-head (HH)/head-to-tail (HT) formation are 17.6/16.3 kcal/mol(1), 17.7/14.8 kcal/mol(2),17.7/17.3 kcal/mol(3),18.9/18.0 kcal/mol(4), and 22.4/21.7 kcal/mol(5). Corresponding values for (G-Pt-A) HH/HT formation are 20.8/20.8(1), 24.9/22.9(2), 27.3/21.6(3), 27.5/24.6(4), and 28.1/25.4(5) kcal/mol in turns. The competition reactions reveal that for 1 and 4, methionine residue stabilizes the transition state (ΔGaq/ZPE = 13.1/12.7 kcal/mol) for platination more efficiently than purine bases and other protein residues, while cysteine residue owns the lower barrier height (11.1/13.4/11.8 kcal/mol) for 2, 3, and 5. The binding mechanism of trans platinum complexes containing planar amines, trans-[PtCl2(L)(L′)] (where L = L′ = pyridine; L = NH3, L′ = pyridine, or L′ = 2-picoline, 3-picoline, 4-picoline), with DNA and protein residues has been theoretically investigated. Our calculations reveal that the symmetric compound trans-[PtCl2(pyridine)2] is the most kinetically and thermodynamically preferred one not only for binding with guanine in the first substitution but also for binding with cysteine in the second substitution.

Asymmetric induction in 8π electrocyclizations. Design of a removable chiral auxiliary.

The pseudo C(2) symmetric trans diphenyl oxazoline group acts as an effective chiral auxiliary in the 8π, 6π tandem electrocyclization of a substituted tetraene 1-carboxylic acid. Assignment of absolute stereochemistry to the [4.2.0] bicyclooctadiene product supports a model in which both s-cis and s-trans conformations favor the transition states with the same helical twist. This assignment prefaces the development of analogs of SNF4435 C and D. These natural products demonstrate activity as androgen receptor antagonists and as multidrug resistance (mdr) reversal agents.

ChemInform Abstract: Synthesis of Extra Long-Chain 1-Alkanols Through PEG-Assisted Hydroboration of Internal Olefins.

The remarkable catalytic effect of polyethylene glycol (PEG-400) in the hydroboration of C30, C34, and C38 symmetrical trans - olefins leading to the synthesis of the corresponding 1-alkanols in excellent ields is reported. Conversion of olefins (1,a–c) to alcohols (2,a–c) via hydroboration with diborane in presence of PEG-400

Structure and conformational dynamics of the cyclopropanecarbaldehyde molecule in the ground (Sb0) and lowest excited (Tb1 and Sb1) electronic states

The structure and conformational dynamics of nonrigid cyclopropanecarbaldehyde (CPCA) molecule in the ground (Sb0) and lowest excited triplet (Tb1) and singlet (Sb1) electronic states were calculated using the MP2, DFT, CASSCF, CASPT2, and CCSD quantum chemical methods. According to ab initio calculations, in the Sb0 electronic state there are two symmetrical (cis and trans) conformers of the CPCA molecule. Excitation of the CPCA molecule to the ?1 and S1 electronic states causes significant structural changes: carbonyl CCHO fragment becomes nonplanar, cyclopropane fragment rotates around the C–C bond, thus changing the relative positions of the formyl and cyclopropane fragments. Using sections of the potential energy surfaces (PES) of the CPCA molecule in the Tb1 and Sb1 states, we calculated the torsion and inversion wave functions and vibrational transition energies. The results obtained suggest a strong coupling of the torsion and inversion motions in the Tb1 and Sb1 excited states.

Spectroscopic and Theoretical Studies on Symmetric Aryl Azines

Azines, which closely resemble azobenzenes, have important applications in the field of nonlinear optics. NMR and IR spectroscopic study of some symmetric aryl azines has been undertaken with the aid of ab initio theoretical calculations. All data indicated that the structure of azine and substituted azines is the symmetric trans form.

Donor−Acceptor Interactions and Electron Transfer in Cyano-Bridged Trinuclear Compounds

The NIR donor-acceptor charge transfer (DACT) bands of the series of trinuclear complexes trans-[(NC)5Fe(II/III)(mu-CN)RuIIL4(mu-NC)FeIII(CN)5](5/4-) (L= pyridine, 4-tert-butylpyridine, and 4-methoxypyridine) are analyzed in terms of a simplified molecular orbital picture that reflects the interaction between the donor and acceptor fragments. The degree of electronic coupling between the fragments is estimated by a full fit of the DACT band profiles according to a three-state model inspired in the Mulliken-Hush formalism. The information is complemented with determinations performed on the asymmetric heterotrinuclear species trans-[(NC)5CoIII(mu-CN)RuII(py)4(mu-NC)FeIII(CN)5]4-, whose preparation is reported here for the first time. The analysis of the NIR spectra of the symmetric trans-[(NC)5FeIII(mu-CN)RuIIL4(mu-NC)FeIII(CN)5]4- species reveals a low degree of mixing between the terminal acceptor fragments and the bridging moiety containing RuII, with H12 values between 1.0 x 10(3) and 1.5 x 10(3) cm-1. The reorganization energy contributions seem to be the same for the three species, even when the spectra were recorded in different media. This observation also applies for the CoIII-substituted compound. The computed potential energy surfaces (PES) of the ground state for these complexes show only one stationary point, suggesting that the FeII-RuIII-FeIII (or FeII-RuIII-CoIII) electronic isomers are not thermally accessible. One-electron reduction leads to asymmetric trans-[(NC)5FeII(mu-CN)RuIIL4(mu-NC)FeIII(CN)5]5- compounds with potentially two DACT bands involving the RuII and the FeII donor fragments. These species reveal a similar degree of electronic mixing but the PES shows three minima. We explore the role of the bridging fragment in the long-range thermally induced electron transfer between the distant iron centers. The results suggest that superexchange and hopping might become competitive paths, depending on the substituents in the bridging fragment.

SCC‐DFTB energy barriers for single and double proton transfer processes in the model molecular systems malonaldehyde and porphycene

AbstractSelf‐consistent charge–density functional tight‐binding SCC‐DFTB is a computationally efficient method applicable to large (bio)molecular systems in which (bio)chemical reactions may occur. Among these reactions are proton transfer processes. This method, along with more advanced ab initio techniques, is applied in this study to compute intramolecular barriers for single and double proton transfer processes in the model systems, malonaldehyde and porphycene, respectively. SCC‐DFTB is compared with experimental data and higher‐level ab initio calculations. For malonaldehyde, the SCC‐DFTB barrier height is 3.1 kcal/mol in vacuo and 4.2 kcal/mol in water solution. In the case of porphycene, the minimum energy pathways for double intramolecular proton transfer were determined using the conjugate peak refinement (CPR) method. Six isomers of porphycene were ordered according to energy. The only energetically allowed pathway was found to connect two symmetrical trans states via an unstable cis‐A isomer. The SCC‐DFTB barrier heights are 11.1 kcal/mol for the trans‐cis‐A process, and 7.4 kcal/mol for the reverse cis‐A‐trans one with the energy difference of 3.7 kcal/mol between the trans‐ and cis‐A states. The method provides satisfactory energy results when compared with reference ab initio and experimental data. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006

Asymmetric Induction in the Conjugate Addition of Thioacetic Acid to Methacrylamides with Chiral Auxiliaries.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Substitution and Intramolecular Rearrangement of trans‐[ReO(X)(acac2en/pn)]0/+ (X = OH2 or Cl−) to Yield Asymmetric cis‐[ReO(Y)(acac2en/pn)] Complexes with Cyanide and Thiocyanate

Asymmetric Re(V) oxo complexes of the type cis‐[ReO(Y)(acac2en/pn)] (Y = CN−, NCS−) were generated from the symmetric precursors trans‐[ReO(X)(acac2en/pn)]0/+ (X = H2O, Cl−) by reaction with cyanide and thiocyanate. The products were characterized using standard spectroscopic methods, elemental analyses and single crystal X‐ray diffraction. The crystallographic data for the structures reported are as follows: cis‐[ReO(NCS)(acac2pn)] (H20C14N3O3SRe), 1, monoclinic (P21/n), a = 8.0047(6) Å, b = 13.6118(10) Å, c = 30.597(2) Å, β = 96.571(1)°, V = 3311.9(4) Å3, Z = 8; cis‐[ReO(CN)(acac2pn)] (H20C14N3O3Re), 2, monoclinic (P21/n), a = 9.5139(12) Å, b = 14.0625(18) Å, c = 12.2343(3) Å, = 107.286(2)°, V = 1562.9(3) Å3, Z = 4; cis‐[ReO(NCS)(acac2en)] (H18C13N3O3SRe), 3, monoclinic (P21/c), a = 17.1965(19) Å, b = 12.7416(14) Å, c = 15.7270(17) Å, = 110.589(2)°, V = 3225.9(6) Å3, Z = 8. The authors would like to gratefully acknowledge financial support from DOE grants DE‐FG02‐93ER61661 (JLG) and DE‐FG2‐01ER63192 (HPE) from the Radiochemistry Education Award Program administered by the South Carolina Universities Research and Education Foundation (under U.S. Department of Energy Cooperative Agreement #DE‐FC09SR18262), Mallinckrodt Medical, Inc. (St. Louis, MO) and the National Science Foundation NSF CHE 9221835 (250 MHz NMR).

Singlet Nitric Oxide Dimer Revisited: An Unexpected High Stability Isomer

A new form of the asymmetric cis isomer of the nitric oxide dimer, a cyclic parallelogram, has been found and characterized as the second most stable conformation by ab initio computational methods. Optimum equilibrium geometries, energetics, and harmonic frequencies are computed for the cyclic structure and the more common symmetric cis and trans isomers at the levels of second-order perturbation theory (MP2) and coupled-cluster theory limited to double excitations (CCD) using the 6-311G(2d) and 6-311+G(2d) basis sets. Single-point, more highly correlated calculations are then performed at these CCD optimum geometries. In addition, second-order geometries and frequencies are computed using the larger 6-311G(3df) basis, and single-point MP2 calculations are performed at these geometries using the Aug-cc-pVTZ and Aug-cc-pVQZ basis sets. At the highest levels of theory considered, the cyclic isomer lies within 17 kJ/mol of the symmetric cis global minimum and is more stable than the often-studied symmetric trans conformation.

Jet-Cooled Multiphoton Ionization Spectroscopy of the iso-Butanal 3s←n Rydberg Transition

We report the results of a study on the vibrational structure in the (n, 3s) Rydberg state of iso-butanal, carried out via 2+1 multiphoton ionization spectroscopy in a supersonic expansion. Spectra were recorded for both the normal species, (CH3)2CHCHO, and the deuterated isotopomer, (CH3)2CDCHO. The spectra show a complicated vibrational pattern attributable to the gauche (C1) conformer which is known to be 250 cm−1 lower in energy than the more symmetric trans (Cs) conformer. The spectra are dominated by the low-frequency formyl torsion which appears in combination with the two methyl torsions (in-phase and out-of-phase) and with several skeletal modes. Vibrational assignments have been aided by ab initio calculations of the (n, 3s) Rydberg state.

Characteristic Phase Transition of [C5H5NH]SbBr4 Having a Hypervalent Bond Studied by Single Crystal X-Ray Diffraction and 2H NMR

Abstract A characteristic second-order phase transition (Ttr = 251 K) of pyridinium tetrabromoantimonate(III) having hypervalent bonds was studied by means of the single-crystal X-ray diffraction and 2H NMR. The SbBr4- anion in [C5H5NH]SbBr4 forms an infinite zigzag chain of irregular SbBr6 octahedra by sharing two edges. This SbBr4- anion has C2 symmetry on the Sb atom perpendicular to the infinite chain. Hence, each octahedron has one symmetric trans Br(2)-Sb-Br(2) bond and two asymmetric trans Br(1)-Sb···Br(2) above Ttr. However, a structural refinement on Phase II at 110 K revealed a characteristic deformation of one symmetric trans Br(2)-Sb-Br(2) bond to an asymmetric one, i.e., one Sb-Br(2) bond becomes shorter by 0.113(2) Å and the other bond located at the trans position becomes longer by 0.129(2) Å. The structural refinement and the 2H NMR on an N-deuterated analog suggest that the N-H···Br hydrogen bond stabilizes the asymmetric trans Br-Sb···Br bond.

Synthesis of a new, C 2 Symmetric α,α - Bis-(Carboxymethyl) Substituted Nitroxide

The novel, diastereomeric meso- (cis) and (±)- (trans) nitroxides 2,5-dicarboxymethyl-2,5-dimethylpyrrolidine-1-oxyl have been synthesized via a dienolate based strategy. Both optically pure enantiomers of the C 2 symmetric trans diastereomer have been obtained via resolution of the corresponding amine with dibenzoyltartaric acid.

Outer-sphere redox reactions of (N)5-macrocyclic cobalt(III) complexes. A temperature and pressure dependence kinetic study on the influence of size and geometry of different macrocycles

Outer-sphere redox reactions between [Co(N)5H2O]3+/[Co(N)5OH]2+ ((N)5=tetraazacycloamine ligand) and [Fe(CN)6]4− have been studied as a function of (N)5, temperature and pressure. The effect of the size of the (N)5 skeleton has been investigated to establish possible correlations between, on the one hand, the size, geometry and charge of the cobalt(III) complex and, on the other hand, the outer-sphere formation constant, the electron-transfer rate constant, and the thermal and baric activation parameters. The values obtained indicate that the outer-sphere formation constants are, within experimental error, the same for all the systems studied. The electron-transfer rate constants for the [Co(N)5H2O]3+ complexes increase on increasing the size of the macrocyclic ligand independently of its cis or trans geometry (from 2.3×10−4 s−1 (13-membered macrocycle) to 3.4×10−1 s−1 (16-membered macrocycle) at P=1 atm, 25°C, I=1.0 M). For the [Co(N)5OH]2+ complexes these differences are significantly smaller (from 1.1×10−3 to 20×10−3 s−1 under the same conditions). The values for the first-order rate constants for the hydroxo complexes are one or two orders of magnitude smaller, as found for simpler pentaamine systems; only for the 13-membered macrocyclic [Co(N)5OH]2+ complex is the trend inverted. The thermal and pressure activation parameters are those expected for these types of reactions and are interpreted in view of a combined effect of electrostatic and hydrogen bonding interactions. In this respect, the highly symmetrical trans 14-membered (N)5 macrocyclic systems show an important increase of 10–20 cm3 mol−1 in the value of ΔV≠ when compared with the equivalent cis systems.

Infrared Spectroscopic Characterization of Chromium Carbonyl Species Formed by Ultraviolet Photoreduction of Silica-Supported Chromium(VI) in Carbon Monoxide

The molybdenum carbonyl species formed by ultraviolet photoreduction of Mo[sup 6+]SiO[sub 2] in CO were characterized with Fourier transform infrared spectroscopy and temperature-programmed decomposition (TPDE). Mo[sup 6+]SiO[sub 2] samples containing 0.07-6.4% Mo were prepared from MoCl[sub 5], Mo[sub 2]([eta][sup 3]-C[sub 3]H[sub 5])[sub 4], and (NH[sub 4])[sub 6]Mo[sub 7]O[sub 24][center dot]4H[sub 2]O. Four molybdenum carbonyl species have been identified: mer-Mo[sup 4+](CO)[sub 3], cis-Mo[sup 4+](CO)[sub 2], linear Mo[sup 4+](CO), and Mo(CO)[sub 6]. The stoichiometry of photoreduction, decomposition, and reoxidation supports the +4 oxidation state for the mono-, di-, and tricarbonyls. The C[sub 2v] symmetry of mer-Mo(CO)[sub 3] resulted in an IR spectrum consisting of a weak (A[sub 1])[sub 1] symmetric trans C-O stretch at 2181 cm[sup [minus]1], a strong B[sub 2] antisymmetric trans C-O stretch at 2141 cm[sup [minus]1], and a strong (A[sub 1])[sub 2] cis C-O stretch at 2108 cm[sup [minus]1]. The mer-Mo(CO)[sub 3] structure successfully predicted the observed frequencies and intensities of partially substituted Mo([sup 12]C[sup 16]O)[sub x]([sup 13]C[sup 16]O)[sub 3[minus]x] and Mo([sup 12]C[sup 16]O)[sub x]([sup 13]C[sup 18]O)[sub 3[minus]x] (x = 1, 2). Mo(CO)[sub 3] was stable at 300 K with CO partial pressures above 60 Torr. At 193 K, this species was stable under vacuum. Evacuation of mer-Mo(CO)[sub 3] more » at 300 K led to CO ligand loss, resulting in the sequential formation of cis-Mo(CO)[sub 2], linear Mo(CO), and finally, CO-free Mo[sup 4+]. The tricarbonyl assignment is supported by the TPDE pattern, in which two CO ligands were released near 350 K, followed by desorption of the final CO group near 440 K. The stable species are photoformed in the sequence mer-Mo[sup 4+](CO)[sub 3], cis-Mo[sup 4+](CO)[sub 2], and Mo(CO)[sub 6]. 31 refs., 9 figs., 4 tabs. « less