Search results for "Base"

Strong donor–acceptor couplings in a special pair-antenna model

2010

A special pair model composed of two cofacial zinc porphyrins (acceptor) linked to a free base (donor) acts as an energy transfer dyad. Despite the absence of conjugation, ππ*/charge transfer excited states and ultrafast energy transfer (∼5 ps) are noted.

Excitation of Nucleobases from a Computational Perspective I: Reaction Paths

2013

The main intrinsic photochemical events in nucleobases can be described on theoretical grounds within the realm of non-adiabatic computational photochemistry. From a static standpoint, the photochemical reaction path approach (PRPA), through the computation of the respective minimum energy path (MEP), can be regarded as the most suitable strategy in order to explore the electronically excited isolated nucleobases. Unfortunately, the PRPA does not appear widely in the studies reported in the last decade. The main ultrafast decay observed experimentally for the gas-phase excited nucleobases is related to the computed barrierless MEPs from the bright excited state connecting the initial Franck…

Understanding the mechanism of the Povarov reaction. A DFT study

2014

The molecular mechanism of the Povarov reaction in acetonitrile has been studied at the MPWB1K/6-311G** level of theory. This reaction follows a domino process that comprises two sequential reactions: (i) a Lewis acid catalysed aza-Diels–Alder (A-DA) reaction between a N-aryl imine and a nucleophilic ethylene yielding a formal [4 + 2] cycloadduct; (ii) a stepwise 1,3-hydrogen shift at this intermediate affording the final tetrahydroquinoline. At this computational level, the Lewis acid catalysed A-DA reaction presents a two-step mechanism as a consequence of the large stabilisation of the corresponding zwitterionic intermediate. Our study allows establishing that the N-aryl substituent has …

A molecular electron density theory (MEDT) study of the role of halogens (X2= F2, Cl2, Br2and I2) on the aza-Michael-addition reactions

2020

Using the Molecular Electron Density Theory (MEDT), a set of uncatalyzed and X2 molecule-catalyzed (X2 = F2, Cl2, Br2, or I2) aza Michael addition reactions (aza-MARs) between pyrrolidine (PYR) and methyl acrylate (MA) have been studied in the gas phase and in dichloromethane (DCM) medium from the kinetics and molecular mechanism aspects. Analysis of the conceptual DFT reactivity indices indicates that the coordination of the X2 molecules to the oxygen of the MA's carbonyl group increases both the softness and the electrophilic character of MA, thus explaining the catalytic role of the X2 molecules. The nucleophilic attack of the nitrogen of PYR on the MA's β conjugated carbon is the rate-d…

Mono- and Tripodal Porphyrins: Investigation on the Influence of the Number of Pyrene Anchors in Carbon Nanotube and Graphene Hybrids.

2020

A series of molecular precursors, containing one (1 and 3) or three (2 and 4) pyrene anchors, covalently linked to porphyrins (free base or Zn), were prepared and characterized. All of them enable ...

Malonic acid: A multi-modal bridging ligand for new architectures and properties on molecule-based magnets

2003

Abstract In this work, we show how the design of one-, two- and three-dimensional materials can strongly benefit from the use of crystal engineering techniques, which can give rise to structures of different shapes, and how these differences can give rise to different properties. We will focus on the networks constructed by assembling malonate ligands and metal centres. The idea of using malonate (dianion of propanedioic acid, H 2 mal) is that they can give rise to different coordination modes with the metal ions bind. Extended magnetic networks of dimensionalities 1 (1D), 2 (2D) and 3 (3D) can be chemically constructed from malonato-bridged metallic complexes. These coordination polymers b…

Layered Molecule-Based Magnets Formed by Decamethylmetallocenium Cations and Two-Dimensional Bimetallic Complexes [MIIRuIII(ox)3]−(MII=;Mn, Fe, Co, C…

2001

Abstract A new series of hybrid organometallic-inorganic layered magnets with formula [Z III Cp * 2 ] [M II Ru III (ox) 3 ] ( Z III =Co and Fe; M II =Mn, Fe, Co, Cu, and Zn; ox=oxalate: Cp * =pentamethylcyclopentadienyl) has been prepared. All of these compounds are isostructural to the previously reported [ Z III Cp * 2 ] [ M II M III (ox) 3 ] ( M III =Cr, Fe) series and crystallize in the monoclinic space group C 2/ m , as found by powder X-ray diffraction analysis. They are novel examples of magnetic materials formed by bimetallic oxalate-based extended layers separated by layers of organometallic cations. The magnetic properties of all these compounds have been investigated (ac and dc m…

Molecule-Based Magnets Formed by Bimetallic Three-Dimensional Oxalate Networks and Chiral Tris(bipyridyl) Complex Cations. The Series [ZII(bpy)3][ClO…

2000

The synthesis, structure, and physical properties of the series of molecular magnets formulated as [ZII(bpy)3][ClO4][MIICrIII(ox)3] (ZII = Ru, Fe, Co, and Ni; MII = Mn, Fe, Co, Ni, Cu, and Zn; ox = oxalate dianion) are presented. All the compounds are isostructural to the [Ru(bpy)3][ClO4][MnCr(ox)3] member whose structure (cubic space group P4(1)32 with a = 15.506(2) A, Z = 4) consists of a three-dimensional bimetallic network formed by alternating MII and CrIII ions connected by oxalate anions. The identical chirality (lambda in the solved crystal) of all the metallic centers determines the 3D chiral structure adopted by these compounds. The anionic 3D sublattice leaves some holes where th…

Cyclizations via Frustrated Lewis Pairs: Lewis Acid Induced Intramolecular Additions of Amines to Olefins and Alkynes

2010

ChemInform Abstract: Intramolecular Michael Reaction of tert-Butylsulfinyl Ketimines: Asymmetric Synthesis of 3-Substituted Indanones.

2012

The reaction proceeds in the presence of the Ruppert—Prakash reagent (Tms-CF3) with either TBAT or TBAF as a base.