The origins of cycloaddition selectivities and chirality controls in particular and challenging photochemical reactions were examined. The profiles of the energies and stereochemical changes of the photoreactions were characterized by molecular simulations using dynamic molecular orbital methods. The photoreactions possess particular factors which are not explained by the frontier molecular orbital (FMO) theory. Particular photoreactions are examined by following the addition selectivities and two chiral controls by use of chiral hosts. (1) Species-(singlet or triplet), peri-, site-, regio-, and stereo-selectivities in the [2 + 2]cycloadditions and [4 + 4]cycloadditions of 2-pyridone (1). (2) Inversion of regioselectivity (hh/ht ratio) by the linkage-length in intramolecular [2 + 2]cycloadditions of α,β-unsaturated furanones 7 and by the alkene ring-size in intermolecular [2 + 2]cycloadditions of cycloalkenecarboxylates 11–13 with 2-cyclohexenone (10). (3) The occurrence of the hydrogen-shift reaction in the [2 + 2]photocycloaddition system between 4-hydoxycoumarin (17) and 3,4-dihydro-2H-pyran (18o). (4) Chiral control of selective [4π]-electrocyclic isomerizations of 1 to photopyridone 20 by hydrogen-bonding of chiral amide hosts 21. The singlet excited state, 1* was inferred to be enantiomeric conformers, 1*(+) and 1*(−), and the complex 1·(l)-21 proceeds to 1*(+)·(l)-21, followed by quenching to (R)-20. (5) Sensational chiral isomerization of (Z)-cyclooctene (28Z) to chiral (E)-cyclooctene (29E) by chiral benzenepolycarboxylates (30). 28Z was inferred to accompany asymmetric 28Z and the diastereomeric exciplexes Ex1 (28Z·30*) and proceeds with chiral isomerization via the one-sided rotation to Ex2 (29E*·30), followed by quenching to chiral 29E. The molecular simulations for the photoreactions by MOPAC-PM5, (PM3 for hydrogen-bonding), UCIS (for singlets), and UB3LYP (for triplets) are found to be successful and show that the origin of the photoreaction selectivities is essentially determined by the first step (TS1) energies and the stereochemistries are dependent on the excited species presented in the Concluding Remarks. We also propose some applications of the molecular simulations.
Origins of challenging enantiodifferentiating isomerizations and inversions of cycloaddition regioselectivity at several photoreactions were elucidated by molecular simulation. The energy and stereochemical properties depending on the excited species and on the TS1 are revealing of hydrogen-bondings and the attractive parts.
A procedure to prepare macroporous silica gels from an acid-catalyzed tetraethoxysilane (TEOS)–water binary system was developed, and the macroscopic morphology formation was examined at a range of conditions under controlled reaction temperature. This procedure involves two-step mixing of TEOS and water containing pH control agents. The gel morphology is significantly influenced by the solution composition in each mixing step, even if the overall solution composition is unchanged. The macroscopic morphology is formed by phase separation between hydrophobic silica oligomers modified by unhydrolyzed ethoxy groups and hydrophilic solvent mixture consisting of water and ethanol generated from TEOS. The morphology can be described as an aggregation of macroscopic particles, which are most likely formed by the spinodal decomposition and subsequent fragmentation of the silica-rich phase occurring at the solvent-rich side of a miscibility gap. The resultant macroporous gels are dried in a relatively short time to obtain crack-free monolithic silica xerogels, which are useful as silica glass precursors.
Dependence of macroscopic gel morphology on solution composition and preparation conditions is examined for a phase separating mixture of tetraethoxysilane and water, a simple gelling system attractive for preparation of monolithic silica xerogels.
DFT-B3LYP and CASSCF calculations have been performed using a 6-31G* basis set to study photocycloaddition reactions of biradicals, generated by irradiation of 6-amino-2-(3-thienoyl)-1,4-benzoquinone, with ethylene. The calculated parameters of biradicals and transition states have also been compared with ground state parameters to completely elucidate the reaction mechanism of [2 + 2] and [3 + 2] photocycloaddition reactions. Preference for a particular cycloaddition pathway is ascertained by the relative stability between initially formed triplet biradical and another triplet biradical formed by hydrogen shift.
Neutron diffraction measurements were carried out on aqueous alkaline 2 mol % glycine heavy water solutions absorbing CO2. 14N/15N isotopic substitution was applied to obtain information on the molecular structure of glycine carbamate formed in the solution and the hydration structure around the nitrogen atom of the carbamate molecule. The least-squares fitting analysis of the higher-Q region of the observed first-order difference function Δ′N(Q) between 14N- and 15N-enriched sample solutions revealed that the intramolecular distances within the carbamate molecule, r(N–CC) = 1.58(1) Å and r(CC–OC) = 1.25(1) Å, where CC and OC denote the carbamate carbon and oxygen atoms, respectively. It was shown that on the average 2.1(2) D2O molecules were hydrogen-bonded to the amino-hydrogen atoms of the carbamate molecule with the intermolecular distances of r(N···OW) = 2.86(3) Å and r(N···DW) = 3.18(5) Å (OW: water oxygen, DW: water deuterium atoms), respectively.
Polarized Raman spectra for concentrated aqueous KX solutions (X: Cl, Br, NO3, and SCN) were measured in the frequency range of 30 ≤ ≤ 1000 cm−1 in order to find the totally symmetric stretching vibrational mode of hydrated K+. The observed polarized peak intensities of the intermolecular vibrational mode at = 160–180 cm−1 in the isotropic spectra for KCl and KBr solutions exhibit systematic increase with increasing solute content. Polarized components at = 166 and 167 cm−1 were observed in the isotropic spectra for 5 mol % KNO3 and 7 mol % KSCN solutions, respectively. The position of these polarized peaks were found to shift to lower frequency by 7–15 cm−1 in D2O solutions, which is consistent with the expected value of the H/D isotopic shift calculated for the totally symmetric vibrational mode of the hydrated K+, K+(H2O)6.
Mononuclear [Fe(H2L2-Et-5-Me)2]2+ and dinuclear [Fe2(H2L2-Et-5-Me)3]4+ complexes, where H2L2-Et-5-Me denotes 2-ethyl-5-methylimidazole-4-carbaldehyde azine, were prepared and isolated as the perchlorate salts, and their structures and magnetic properties were studied. In the mononuclear complex, the ligand acts as an unsymmetrical tridentate ligand with two imidazole nitrogen atoms and one azine nitrogen atom. The complex was in the HS state above 50 K. In the dinuclear complex, each ligand acts as a dinucleating ligand employing four nitrogen atoms to form a triple helicate structure. Two types of crystals, plates and blocks, were isolated for the dinuclear complex. The plate crystals exhibited a sharp spin transition, [LS–HS] ↔ [HS–HS], with no [LS–LS] state being observed. The block crystals remained in the [HS–HS] state above 50 K.
197Au Mössbauer spectra have been measured on a series of homovalent and heterovalent dinuclear gold complexes containing the 2-C6F4PPh2 ligand. The correlation plot indicates that the electron densities of the 6s and 6p orbitals of the gold atoms in these complexes are less than those of their protio and 6-methyl analogs, reflecting the electron-withdrawing property of the fluorine substituents.
The nickel-catalyzed electroreductive coupling of a benzylic chloride with an acyl donor reagent in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate has been studied in the preparative scale to obtain aryl propan-2-ones in galvanostatic mode. Poor solubility of metallic salts prevents the use of the sacrificial anode process in an undivided cell. Moderate chemical yields are obtained within a divided cell configuration using an anionic membrane as a separator, which shows the compatibility of ionic liquids with this kind of electrochemical device. Aryl propan-2-ones were prepared with chemical yield up to 65%. Cyclic voltammetry and UV–vis spectroscopy confirm that the mechanism is the same in the ionic liquid and in a classical molecular solvent such as DMF. Nevertheless, degradation of the imidazolium cation induced by redox catalysis involving the bipyridine ligand has been observed, which explains the low faradaic yields.
The reaction of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with compounds possessing two vicinal chlorine atoms activated toward nucleophilic substitution has been studied. All derivatives bearing a 2,3-dichloropyrazine moiety react with DBU leading to fluorescent dyes. Among others, only 2,3-dichloro-1,4-naphthoquinone reacts giving the expected pentacyclic product albeit in a very low yield and accompanied by the product of hydrolysis. Spectroscopic properties of the synthesized compounds were studied. The dye formed from 5,6-dichloro-2,3-dicyanopyrazine exhibits a very high Stokes shift and strong dependence of the fluorescence quantum yield on solvent polarity.
A novel method for the synthesis of chiral hydroisoquinolines by asymmetric Diels–Alder reaction of nitrogen-containing dienophiles and suitably protected aminosiloxybutadienes has been developed. The product could be a key intermediate for synthesis of manzamine alkaloids.
The stereocenter in the intermediate alcohol (86% ee), created by enantioselective oxazaborolidinone-promoted aldol reaction, was transferred to the stereocenter in the cyclohexanone ring, necessary for (S)-ketamine, via allyl cyanate-to-isocyanate rearrangement. The second asymmetric synthesis of (S)-ketamine has been achieved (87% ee).
All-cis poly(p-phenylenevinylene)s (PPVs) prepared by Suzuki–Miyaura-type polycondensation of (Z,Z)-1,4-bis(2-bromoethenyl)benzene with 2,5-dioctyloxybenzene-1,4-diboronic acid undergo photo-induced insolubilization in thin films, along with cis-to-trans isomerization of vinylene linkages to give all-trans PPVs. This phenomenon has been investigated using all-cis and all-trans PPVs with a range of molecular weights and terminal structures. The amounts of PPVs remaining on quartz substrates, after UV-irradiation on spin-coated films, followed by rinsing twice with CHCl3, are dependent on the geometries of vinylene linkages, molecular weights, and terminal structures of the starting PPVs. It has been found that the all-cis configuration is of particular importance for insolubilization. The insolubilized films exhibit charge-carrier mobility (μFET) up to 1.6 × 10−4 cm2 V−1 s−1.
The biomass carbon ratios of various chemical products were studied. The biomass carbon ratios of chemicals such as polymers, their monomers, starches, cellulose, calcium carbonate, charcoal, ethanol, and polymer blends were estimated by the ratios of 14C to 12C measured by accelerator mass spectrometry (AMS) based on ASTM D 6866. Preparations of the gaseous and liquid samples for the AMS measurements are described, and the pretreatment for carbonate is also explained. Repeatability and accuracy of the biomass carbon ratio evaluation by AMS are discussed. It was found that a new correction factor is necessary for cellulose other than 0.93, which is regulated as the correction factor for present modern carbon newer than 1950 in ASTM D 6866. The developed sample preparations of gaseous materials and carbonate were confirmed to be applicable for the AMS measurement of the biomass carbon ratio. The repeatability and accuracy of the biomass carbon ratio evaluation by AMS were confirmed for ethanol derived from biomass (bioethanol), a polymer blend of biomass-based poly(lactic acid) (PLA), and petroleum-based poly(butylene succinate) (PBS). Standard deviations of the bioethanol and the blend of PLA and PBS are 0.36 and 0.84%, respectively. The biomass carbon ratio evaluation by AMS has been proposed for the International Standard (ISO).