Stabilization Energy (stabilization + energy)

Distribution by Scientific Domains

Kinds of Stabilization Energy

  • aromatic stabilization energy


  • Selected Abstracts


    Electronic properties of tricoordinated phosphorus in hexagonal phosphininium compounds and molecular aromaticity

    JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2007
    Wei-Qi Li
    Abstract Calculations with B3LYP within quantum chemical density functional theory have been carried out for 1- H -phosphininium cation and a series of 1- R -phosphininium molecules (R = cyclopentadiene, , and , pyrroles, , and , phosphole, C5BH5 and CH2). The negative nuclear-independent chemical shift values and the positive aromatic stabilization energies confirm that they are aromatic compounds. In particular, the 1- H -phosphininium cation even exhibits stronger aromatic character than the well-known aromatic phosphinine. The aromatic substituents have strong capability to attract electrons. It is the conjugation and aromaticity that keeps the stability and conformations of the molecules investigated. Owing to the perturbation of the aromatic substituted groups, the predicted large T values and the enlarged HOMO-LUMO gap of the phosphininium cation indicate that these compounds are expected in experiment. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source]


    Ab initio and DFT studies on van der Waals trimers: The OCS · (CO2)2 complexes

    JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2002
    H. Valdés
    Abstract Ab initio calculations [MP2, MP4SDTQ, and QCISD(T)] using different basis sets [6-31G(d,p), cc-pVXZ (X = D, T, Q), and aug-cc-pVDZ] and density functional theory [B3LYP/6-31G(d,p)] calculations were carried out to study the OCS · (CO2)2 van der Waals trimer. The DFT has proved inappropriate to the study of this type of systems where the dispersion forces are expected to play a relevant role. Three minima isomers (two noncyclic and one cyclic) were located and characterized. The most stable isomer exhibits a noncyclic barrel-like structure whose bond lengths, angles, rotational constants, and dipole moment agree quite well with the corresponding experimental values of the only structure observed in recent microwave spectroscopic studies. The energetic proximity of the three isomers, with stabilization energies of 1442, 1371, and 1307 cm,1, respectively, at the CBS-MP2/cc-pVXZ (X = D, T, Q) level, strongly suggests that the two unobserved structures should also be detected as in the case of the (CO2)3 trimer where both noncyclic and cyclic isomers have been reported to exist. The many-body symmetry-adapted perturbation theory is employed to analyze the nature of the interactions leading to the formation of the different structures. The three-body contributions are small and stabilizing for the two most stable structures and almost negligible for the cyclic isomer. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 444,455, 2002; DOI 10.1002/jcc.10041 [source]


    Deprotonation and radicalization of glycine neutral structures

    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2008
    Gang Yang
    Abstract Ab initio calculations at MP2/6-311++G(d,p) theoretical level were performed to study the deprotonation and radicalization processes of 13 glycine neutral structures (A. G. Császár, J. Am. Chem. Soc. 1992; 114: 9568). The deprotonation processes to glycine neutral structures take place at the carboxylic sites instead of , -C or amido sites. Two carboxylic deprotonated structures were obtained with the deprotonation energies calculated within the range of 1413.27,1460.03,kJ,·,mol,1, which are consistent with the experimental results. However, the radicalization processes will take place at the , -C rather than carboxylic O or amido sites, agreeing with the experimental results. Seven , -C radicals were obtained with the radical stabilization energies calculated within the range of 44.87,111.78,kJ,·,mol,1. The population analyses revealed that the main conformations of the neutral or radical state are constituted by several stable structures, that is, the other structures can be excluded from the future considerations and thus save computational resources. Copyright © 2007 John Wiley & Sons, Ltd. [source]


    Adsorption of pyridine, ,-picoline and isonicotinonitrile on Ag colloidal particles studied by surface-enhanced Raman scattering spectroscopy

    JOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2005
    Tomoe Osaki
    Abstract The surface-enhanced Raman scattering (SERS) spectra of pyridine and related compounds, ,-picoline and isonicotinonitrile, in Ag colloids were studied. Electron diffraction measurement indicated that the Ag colloidal particles are composed of Ag crystals. Models for the molecules adsorbed on Ag particles were proposed and the optimized geometries of the models were determined through calculations of the stabilization energies due to adsorption made for the models with Gaussian 98 using the Hartree,Fock theory with the 3,21G basis set. The normal vibrations of the molecules adsorbed on Ag particles were calculated using the optimized models and assignments of the vibrational bands of the SERS spectra were made. On the basis of the results obtained, it was concluded that (1) pyridine and related compounds are adsorbed on Ag particles through NAg bonds and (2) the N atoms of the molecules are bound to the pointed ends of the surface of Ag particles on adsorption. Copyright © 2004 John Wiley & Sons, Ltd. [source]


    A CSOV study of the difference between HF and DFT intermolecular interaction energy values: The importance of the charge transfer contribution

    JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2005
    Jean-Philip Piquemal
    Abstract Intermolecular interaction energy decompositions using the Constrained Space Orbital Variation (CSOV) method are carried out at the Hartree,Fock level on the one hand and using DFT with usual GGA functionals on the other for a number of model complexes to analyze the role of electron correlation in the intermolecular stabilization energy. In addition to the overall stabilization, the results provide information on the variation, with respect to the computational level, of the different contributions to the interaction energy. The complexes studied are the water linear dimer, the N -methylformamide dimer, the nucleic acid base pairs, the benzene,methane and benzene-N2 van der Waals complexes, [Cu+ -(ImH)3]2, where "ImH" stands for the Imidazole ligand, and ImH-Zn++. The variation of the frozen core energy (the sum of the intermolecular electrostatic energy and the Pauli repulsion energy) calculated from the unperturbed orbitals of the interacting entities indicates that the intramolecular correlation contributions can be stabilizing as well as destabilizing, and that general trends can be derived from the results obtained using usual density functionals. The most important difference between the values obtained from HF and DFT computations concerns the charge transfer contribution, which, in most cases, undergoes the largest increase. The physical meaning of these results is discussed. The present work gives reference calculations that might be used to parametrize new correlated molecular mechanics potentials. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1052,1062, 2005 [source]


    DommiMOE: An implementation of ligand field molecular mechanics in the molecular operating environment

    JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2005
    Robert J. Deeth
    The ligand field molecular mechanics (LFMM) model, which incorporates the ligand field stabilization energy (LFSE) directly into the potential energy expression of molecular mechanics (MM), has been implemented in the "chemically aware" molecular operating environment (MOE) software package. The new program, christened DommiMOE, is derived from our original in-house code that has been linked to MOE via its applications programming interface and a number of other routines written in MOE's native scientific vector language (SVL). DommiMOE automates the assignment of atom types and their associated parameters and popular force fields available in MOE such as MMFF94, AMBER, and CHARMM can be easily extended to provide a transition metal simulation capability. Some of the unique features of the LFMM are illustrated using MMFF94 and some simple [MCl4]2, and [Ni(NH3)n]2+ species. These studies also demonstrate how density functional theory calculations, especially on experimentally inaccessible systems, provide important data for designing improved LFMM parameters. DommiMOE treats Jahn,Teller distortions automatically, and can compute the relative energies of different spin states for Ni(II) complexes using a single set of LFMM parameters. © 2004 Wiley Periodicals, Inc. J Comput Chem 26: 123,130, 2005 [source]


    Relationship between substituent effect and aromaticity , Part III: naphthalene as a transmitting moiety for substituent effect

    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2007
    Tadeusz M. Krygowski
    Abstract Molecular geometry of 10 isomeric nitronaphtholate ions (excluding peri - and ortho -type substituted systems), 1- and 2-naphtholate ions, 1- and 2-nitronaphthalene, meta - and para -nitrophenolate, phenolate, and nitrobenzene were optimized at B3LYP/6-311G** level of approximation. Substituent effect stabilization energy (SESE), geometry-based aromaticity index HOMA, magnetism-based indices NICS, NICS(1), NICS(1)zz, and parameters characterizing Bond Critical Points (BCP) (,, ,2,, ellipticity, ion/cov) of the Bader AIM theory were used to characterize transmitting properties for substituent effect through the naphthalene moiety. It results from our study that the studied systems could be clearly divided into two groups, (i) a para -type group, where the intramolecular charge transfer between the , -electron donating and , -electron accepting substituents can be described by canonical forms with charge separation (as in the case of para -nitrophenolate) and (ii) a meta -type group, where this transfer requires using canonical forms with double charge separation (as in the case of meta -nitrophenolate). Copyright © 2007 John Wiley & Sons, Ltd. [source]


    NMR spectroscopic characterization of inclusion complexes comprising cyclodextrins and gallated catechins in aqueous solution: cavity size dependency

    MAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2009
    Takashi Ishizu
    Abstract The structure of inclusion complexes of ,-cyclodextrin (,-CD), (,)-gallocatechin gallate (GCg), and (,)-epigallocatechin gallate (EGCg) in D2O was investigated using several NMR techniques. GCg formed a 1:1 inclusion complex with ,-CD in which the A and C rings of GCg were inserted deep at the head of the A ring into the ,-CD cavity from the wide secondary hydroxyl group side. In the 1:1 inclusion complex with GCg and ,-CD, the GCg moiety maintained a conformation in which the B and B, rings of GCg took both pseudoequatorial positions with respect to the C ring. The structure of the inclusion complex of GCg and ,-CD obtained from NMR experiments supported well that determined from PM6 semiempirical SCF MO calculations. However, 1H NMR experiments suggested that EGCg did not form any inclusion complex with ,-CD in D2O. The marked difference between GCg and EGCg in inclusion behavior toward ,-CD may be explained in terms of the stabilization energy calculated with the PM6 method. Copyright © 2008 John Wiley & Sons, Ltd. [source]


    Demonstration of "Möbius" Aromaticity in Planar Metallacycles

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2010
    Michael Mauksch Dr.
    Abstract Möbius aromaticity, predicted by Edgar Heilbronner in 1964, is a stabilizing effect exhibited by 4,n electron fully conjugated cyclic molecules (or transition states) with an odd number of orbital phase inversions. Although it has previously been suggested that this effect might also apply to planar metallacycles in which a transition metal employs a d orbital in ,-type binding mode, only very few examples of stable twisted molecules composed of main group elements are known. We report herein, the first computationally confirmed 4,n,, aromatic planar metallacyclic examples and their building principles. Aromatic stabilization energy (ASE) of a 8,, metalla-cycloheptatriene [Fe(CH)6H2], with four doubly occupied , orbitals and a HOMA value of +0.80 (cf. benzene=+1.0), an NICS(0) value of ,8.5 (benzene=,9.8, NICS=nucleus independent chemical shift), and with one phase inversion, is +27.5,kcal,mol,1 (about two-thirds of the value for benzene). In contrast, an unknown non-Möbius 1,4-dimetallabenzene [Fe2(CH)4H4], also with 8,, electrons, and without phase inversions, has an ASE of ,4.1,kcal,mol,1 and a NICS(0)=+15.6, indicative of antiaromaticity. Aromaticity of the proposed Möbius aromatic metallacycles is confirmed by using magnetic (NICS(0), NICS(1)zz, ,1H) and geometric (HOMA) aromaticity criteria, planarity, and near equalized CC bond lengths, bonding analysis (Wiberg bond indices, NBO, and NLMO analysis). The role of wave function boundary conditions (periodic vs. antiperiodic) in chemistry is further stressed, being equivalent to Zimmerman's concept of nodal parity for Möbius/Hückel systems. [source]


    Is Cyclopropane Really the ,-Aromatic Paradigm?

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 38 2009
    Wei Wu Prof.
    Abstract Dewar proposed the ,-aromaticity concept to explain the seemingly anomalous energetic and magnetic behavior of cyclopropane in 1979. While a detailed, but indirect energetic evaluation in 1986 raised doubts,"There is no need to involve ,,-aromaticity',",other analyses, also indirect, resulted in wide-ranging estimates of the ,-aromatic stabilization energy. Moreover, the aromatic character of "in-plane", "double", and cyclically delocalized ,-electron systems now seems well established in many types of molecules. Nevertheless, the most recent analysis of the magnetic properties of cyclopropane (S. Pelloni, P. Lazzeretti, R. Zanasi, J. Phys. Chem. A2007, 111, 8163,8169) challenged the existence of an induced ,-ring current, and provided alternative explanations for the abnormal magnetic behavior. Likewise, the present study, which evaluates the ,-aromatic stabilization of cyclopropane directly for the first time, fails to find evidence for a significant energetic effect. According to ab initio valence bond (VB) computations at the VBSCF/cc-PVTZ level, the ,-aromatic stabilization energy of cyclopropane is, at most, 3.5,kcal,mol,1 relative to propane, and is close to zero when n -butane is used as reference. Trisilacyclopropane also has very little ,-aromatic stabilization, compared to Si3H8 (6.3,kcal,mol,1) and Si4H10 (4.2,kcal,mol,1). Alternative interpretations of the energetic behavior of cyclopropane (and of cyclobutane, as well as their silicon counterparts) are supported. [source]


    ,,, Energy Separation in Homodesmotic Reactions

    CHEMPHYSCHEM, Issue 12 2005
    Georg Hohlneicher Dr.
    Abstract A well-established quantity for specifying the aromaticity or antiaromaticity of cyclic conjugated molecules is the so-called aromatic stabilization energy (ASE), which can be derived,either experimentally or theoretically,from appropriate homodesmotic reactions. To gain further insight into the origin of aromaticity, several schemes have been devised to partition ASE into nuclear and electronic as well as , and , contributions, some of which have resulted in contradictory statements about the driving force of aromatic stabilization. Currently, these contradictions have not been resolved and have resulted in a confusing distinction between two different types of aromaticity: extrinsic and intrinsic aromaticity. By investigating different homodesmotic reactions we show that, in contrast to ASE itself, the individual contributions that enter the ASE can strongly depend on the type of reaction. Caution is therefore advised if conclusions or physical interpretations are derived from the individual components. The contradictions result from the fact that some reactions suffer from an imbalance in the number of interaction terms at the two sides of the reaction equation. The concept of isointeractional reactions is introduced and results in the elimination of the imbalance. For these reactions, the contradictions disappear and the distinction between intrinsic and extrinsic aromaticity becomes unnecessary. As far as the ,,, partitioning is concerned, several schemes proposed in the literature are compared. Contradictory results are obtained depending on the partitioning scheme and reaction used. In this context, it is demonstrated that for the partitioning of the electron,electron interaction, the scheme introduced by Jug and Köster is the one that is most theoretically grounded. [source]


    The Origin of Aromaticity: Important Role of the Sigma Framework in Benzene

    CHEMPHYSCHEM, Issue 9 2004
    Borislav Kova
    Abstract The physical nature of aromaticity is addressed at a high ab initio level. It is conclusively shown that the extrinsic aromatic stabilization energy of benzene E(ease)B, estimated relative to its linear polyene counterpart(s), is very well-reproduced at the Hartree,Fock (HF) level. This is a consequence of the fact that the contributions arising from the zero-point vibrational energy (ZPVE) and electron correlation are rather small. More specifically, they yield together 2.0 kcal,mol,1to the destabilization of benzene. A careful scrutiny of the HF energies by virial theorem shows further that the kinetic energies of the , and , electrons E(T) and E(T) are strictly additive in the gauge linear zig-zag polyenes, which also holds for their sum Et(T)HF. This finding has the important corollary that E(ease)Bis little dependent on the choice of the homodesmic reactions involving zig-zag polyenes. A detailed physical analysis of the ,- and ,-electron contributions to extrinsic aromaticity requires explicit introduction of the potential energy terms Vne, Vee, and Vnn, which signify Coulomb interactions between the electrons and the nuclei. The Veeterm involves repulsive interaction V between the , and , electrons, which cannot be unequivocally resolved into , and , contributions. The same holds for the Vnnenergy, which implicitly depends on the electron density distribution via the Born,Oppenheimer (BO) potential energy surface. Several possibilities for partitioning V and Vnnterms into , and , components are examined. It is argued that the stockholder principle is the most realistic, which strongly indicates that E(ease)Bis a result of favorable , -framework interactions. In contrast, the ,-electron framework prefers the open-chain linear polyenes. [source]