Carbon Atoms C3 Research Articles

Photochemical Deracemization of 3-Substituted Oxindoles.

Racemic 3-substituted oxindoles were successfully converted into enantiomerically pure or enriched material (up to 99 % ee) upon irradiation at λ=366 nm in the presence of a chiral benzophenone catalyst (10 mol %). The photochemical deracemization process allows predictable editing of the stereogenic center at carbon atom C3. Light energy compensates for the associated loss of entropy and enables the decoupling of potentially reversible reactions, i.e. a hydrogen atom transfer to (photochemical) and from (thermal) the carbonyl group of the catalyst. The major enantiomer is continuously enriched in several catalytic cycles. The obtained oxindoles were shown to be valuable intermediates for further transformations, which proceeded with complete retention at the stereogenic center.

Photochemical Deracemization of 3‐Substituted Oxindoles

AbstractRacemic 3‐substituted oxindoles were successfully converted into enantiomerically pure or enriched material (up to 99 % ee) upon irradiation at λ=366 nm in the presence of a chiral benzophenone catalyst (10 mol %). The photochemical deracemization process allows predictable editing of the stereogenic center at carbon atom C3. Light energy compensates for the associated loss of entropy and enables the decoupling of potentially reversible reactions, i.e. a hydrogen atom transfer to (photochemical) and from (thermal) the carbonyl group of the catalyst. The major enantiomer is continuously enriched in several catalytic cycles. The obtained oxindoles were shown to be valuable intermediates for further transformations, which proceeded with complete retention at the stereogenic center.

Photochemical Ring Contraction of 5,5-Dialkylcyclopent-2-enones and in situ Trapping by Primary Amines.

If substituted in the 5,5-position, cyclopent-2-enones undergo a smooth photochemical rearrangement to ketenes. A concomitant cyclopropane formation occurs due to a 1,3-shift of the C5 carbon atom from the carbonyl carbon atom (C1) to carbon atom C3. In this study, the cyclopropyl-substituted ketene intermediates were trapped in situ by primary amines providing an efficient entry into 2,2-disubstituted cyclopropaneacetic amides (24 examples, 49-95% yield). A remarkable feature of the reaction is the fact that the photochemical rearrangement can occur from either the first excited singlet (S1) or the respective triplet state (T1). In line with experimental results (triplet quenching, sensitization), XMS-CASPT2 calculations support the existence of efficient reaction pathways to the intermediate ketene both on the singlet and on the triplet hypersurface.

Energy profile analysis, spectroscopic investigations (FT–IR, FT–Raman and FT–NMR), electronic properties, structure‒activity aspects and DFT studies of (1,3‒benzodioxol‒5‒yl)acetic acid

Abstract The interaction of electromagnetic interaction by comprehensive theoretical and experimental FT‒IR, FT‒Raman and FT‒NMR spectroscopic studies of (1,3‒benzodioxol‒5‒yl)acetic acid (BDA) have been carried out. DFT/B3LYP method with 6‒311++G** and cc‒pVTZ basis sets have been used to determine the molecular properties of BDA. Five different conformers I, II, III, IV and V of BDA has been determined by potential energy profile. The most stable BDA molecule adopts a non‒planar (puckered) conformation I. The total energy, heat capacity, entropy, vibrational energy and zero point energy calculated by B3LYP/cc‒pVTZ basis sets are 106.34 kcal mol‒1, 40.22 kcal mol‒1 K‒1, 103.44 kcal mol‒1, 104.56 kcal mol‒1 and 99.72 kcal mol‒1, respectively. The total electron density of the BDA molecule spread between + 5.53e ×10‒2 and ‒5.531e ×10‒2. The electrostatic potential are lie in the range ± 1.123e ×10‒2. In BDA molecule n(O12) → π* C11‒O13 interaction is strongly stablised by 42.5 kcal mol‒1. The carbon atoms C3 and C4 are highly deshielded due to –I effect of highly electronegative oxygen. The symmetrical O‒C‒O vibration is blue shifted by 20 and 24 cm‒1 in FT‒IR and FT‒Raman spectra, respectively, when compared to methylenedioxy benzene. The reactivity order for the electrophilic attack is C9 > C10 > C11 while the reactivity order for the nucleophilic attack is C10 > C9 > C3.

Experimental and computational evidence for hydrogen bonding interaction between 2′-deoxyadenosine conjugate adduct and amino-terminated organic film on Si(001)

A simple method for immobilization of malonaldehyde-acetaldehyde conjugate adduct with DNA base onto an amino-terminated surface of silicon from water solution is proposed. The Si(001) surface which contains OH groups was modified with 3-aminopropyltrimethoxysilane (APTMS) to serve as a linker between the silica surface and the organic adduct. The 2′-deoxyadenosine adduct was adsorbed on the APTMS/Si surface from acetonitrile/water solution. This nucleoside derivative is stable under laboratory conditions and emits a natural fluorescence, allowing for its adsorption on the APTMS/Si surface to be easily verified by fluorescence microscopy, non-contact atomic force microscopy and attenuated total reflectance Fourier transform infrared spectroscopy. The degree of surface coverage by the adduct was evaluated by X-ray photoelectron spectroscopy (XPS). Analysis of the XPS spectra revealed bands at 400.2eV and 533.1eV which are characteristic of a hydrogen bonded –NH2 and –OH group. This observation implies that the free electron donating –NH2 groups from the APTMS layer makes hydrogen bonds with the fluorescent adduct and immobilize it on the surface. The wetting angle of the APTMS/Si surface before and after adsorption of the nucleoside derivative does not differ significantly, which points to the involvement of an – OH group from 2′-deoxyadenosine to be involved in hydrogen bonding. These experimental results were further supported using quantum chemical calculations to demonstrate that the 2′deoxyadenosine adduct makes hydrogen bonds with the APTMS molecule. Furthermore, this hydrogen bond involves the –NH2 group from APTMS and –OH group at carbon atoms C3 and C6 from the deoxyribose ring of 2′deoxyadenosine.

Crystal structure of head-to-head dimers of cholic and deoxycholic acid derivatives with different symmetric bridges

The crystal structure of three head-to-head dimers (having two cholic acid or deoxycholic acid units) linked at carbon atoms C3 by aromatic or alkyl bridges is studied. An internal coordinates system is necessary for describing the relative orientation in the space of the two bile acid residues. Five angles (three torsion and two common ones) are necessary for defining the relative position of both steroid residues in space. Carbon atoms C3 (which always carries a α-hydroxy group in natural bile acids), and C10 and C13 (which always carry β-methyl groups) of each steroid residue are suitable for this purpose. Furthermore, the distance between each C3 carbon atoms of both steroid residues will allow one to locate the steroids in space. The three dimers selected provide a large range of values for these angles. The packing, hydrogen bond network, and location of guest in the three crystals are discussed.

Reaction of an “Invisible” Frustrated N/B Lewis Pair with Dihydrogen

D-(+)-Camphor forms the enamine 2 with piperidine. Compound 2 adds HB(C(6)F(5))(2) at the enamine carbon atom C3 to form a Lewis acid/Lewis base adduct (exo-/endo-isomers of 3). Exposure of 3 to dihydrogen (2.5 bar, room temperature) leads to heterolytic splitting of H(2) to form the H(+)/H(-) addition products (4, two diastereoisomers) of the "invisible" frustrated Lewis pairs (5, two diastereoisomers) that were apparently generated in situ by enamine hydroboration under equilibrium conditions.

Density functional study of the corrosion inhibition properties of 1,2,4-triazole and its amino derivatives

The electronic parameters of plain 1,2,4-triazole and three isomeric forms of amino-1,2,4-triazole have been studied at the B3LYP/6-31G(d,p) level of theory. Their inhibitory effectiveness was investigated by means of chemical reactivity parameters and reactive centers were analyzed on the basis of Fukui indices. The solvent effect on the studied parameters was found to be insignificant. 3-amino-1,2,4-triazole (3-ATA) with preferred corrosion inhibition performance possesses two electrophilic and two nucleophilic attack centers, implying multicenter adsorption of the molecule on a metal surface. Its interaction with the Cu atom is dominated by the electron donation from the Cu atom to the carbon atom C3 and the back-donation from the amino atom N6.

Determination of the g Tensors for the Dominant Stable Radicals in X-Irradiated β-d-Fructose Single Crystals

In spite of recent successful identifications of radicals produced after X-ray irradiation at 10 and 77 K in beta-D-fructose, the structure of the two stable radicals dominating the electron paramagnetic resonance (EPR) spectrum after room temperature irradiation is still unclear. Based on the agreement between proton hyperfine (HF) tensors obtained in electron nuclear double resonance (ENDOR) experiments and the results of single molecule density functional calculations, a model for these radicals, involving OH abstraction at the C2 ring position, had previously been proposed, but this assignment could not be confirmed when the radical was embedded in a crystal environment. In this paper, we therefore provide additional experimental information for these radicals. First, their g tensors are determined from angular dependent ENDOR-induced EPR experiments. The relatively large anisotropy of these tensors is indicative of delocalization of the unpaired electron onto a neighboring oxygen atom. Second, EPR spectra of fructose powders, selectively enriched in (13)C on various ring positions, are presented, demonstrating that the HF interaction with the carbon atom C3 is larger than with the C2. Combining the g tensor, proton and (13)C HF data, we conclude that the structure of the stable radicals differs strongly from that of intact molecules and that further advanced quantum chemical modeling will be required to fully identify them.

High-Precision Catalysts: Regioselective Hydroformylation of Internal Alkenes by Encapsulated Rhodium Complexes

We report the formation of high-precision catalysts using encapsulated rhodium complexes. In the current example, the encapsulated rhodium catalyst shows unprecedented high selectivity in the rhodium-catalyzed hydroformylation of internal alkenes, forming predominantly one of the branched aldehydes. This catalyst system is the first example that is able to discriminate between carbon atoms C3 and C4 in trans-3-octene.

Preparation of Trifluorophosphaneruthenium(II) Complexes from η3:η3-Cyclooctadienediylruthenium(IV) Compounds as Precursors

The dinuclear cyclooctadienediylruthenium(IV) compound [{RuCl2(η3:η3-C10H16)}2] (1) reacts with PCy3 in 2-propanol under an H2 atmosphere to give the hydrido(dihydrogen) complex [RuHCl(H2)(PCy3)2] (2) in nearly quantitative yield. Treatment of 1 with PCy3, PiPr3 or PiPr2Ph under argon affords the mononuclear products [RuCl2(η3:η3-C10H16)(PR3)] (3−5) by chloride-bridge cleavage. The corresponding compound 6 with PF3 as phosphane ligand reacts with PCy3 by nucleophilic attack of PCy3 at the carbon atom C3 of the dienediyl chain to give the zwitterionic η2:η3-alkene(allyl)ruthenium(II) complex [RuCl2{η2:η3-CH2=C(Me)−CH(PCy3)(CH2)2CHC(Me)CH2}(PF3)] (7) the crystal and molecular structures of which have been determined. The reaction of 7 with excess PCy3 in the presence of H2 affords the five-coordinate hydrido compound [RuHCl(PF3)(PCy3)2] (8), which upon treatment with acetylene gives the vinyl derivative [RuCl(CH=CH2)(PF3)(PCy3)2] (9). The related cationic carbene complex [RuCl(=CHCH3)(PF3)(PCy3)2]BF4 (10) is obtained by protonation of 9 with HBF4 in ether. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Rotational band contour analysis in the Ã1A′-[Xtilde]1A′ electronic systems of substituted naphthalenes

The 00 0 bands of the A 1 A′-[Xtilde] 1 A′ systems of 1-fluoro, 1-hydroxy and 1-aminonaphthalene have been investigated by rotational band contour analysis. The 00 0 bands in 1-fluoro and 1-hydroxynaphthalene are 70 per cent type A and 30 per cent type B, and 75 per cent type A and 25 per cent type B hybrids respectively: the electronic transition moment vector has been rotated by about 15° towards the carbon atom C3 by the F and OH substituents compared to naphthalene (in which, in the A-[Xtilde] system, it is along the long in-plane axis). In 1-aminonaphthalene it seems likely that the 00 0 band is predominantly type A, but it could not be observed with sufficient intensity to be able to obtain the excited state rotational constants with any certainty.

Steric influences in radical reactions. Part II. The abstraction of benzylic hydrogen atoms from 1-phenylphthalan, 1,3-diphenylphthalan, and 2-formyl-2′-methylbiphenyl by t-butoxy radicals

Hydrogen-abstraction from 1-phenylphthalan by t-butoxy radicals at 120° liberates both of the radicals in which the free electron is at either of the benzylic carbon atoms C3 and C1, as evidenced by isolation of products resulting from rearrangement of the former radical and from dimerisation of the latter. Abstraction occurs from the methyl group of o-benzoyltoluene to give a radical which dimerises at 30°, but at 125° cyclises, to give ultimately anthraquinone and dianthrone. 1,3-Diphenylphthalan gives mainly 1,2-dibenzoylbenzene, the same product as when the phthalan is heated alone.Abstraction from 2-formyl-2′-methylbiphenyl, at both 30 and 120°, occurs mainly at the aldehyde group; the benzoyl radical so formed then cyclises to 4-methylfluorenone in 60–67% yield. The intramolecular acylation of the radical is believed to be facilitated by steric effects.