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Exploring the Role of Serial Dependence in Visual Time Perception
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"Exploring the Role of Serial Dependence in Visual Time Perception"
Jessica Bertolasi, Davide Esposito, Anna Vitale, Monica Gori
https://doi.org/10.1167/jov.25.8.
RESONANCE-ASSISTED HYDROGEN-BONDING .3. FORMATION OF INTERMOLECULAR HYDROGEN-BONDED CHAINS IN CRYSTALS OF BETA-DIKETONE ENOLS AND ITS RELEVANCE TO MOLECULAR ASSOCIATION
No full textThe beta-diketone enol (or enolone) HO-C=C-C=O fragment produced by enolization of beta-diketones is known to form strong intramolecular O-H...O hydrogen bonds where the decrease of the O...O contact distance (up to 2.40 angstrom) is correlated with the increased pi-delocalization of the O-C=C-C=O heteroconjugated system, the phenomenon has been interpreted by the resonance-assisted hydrogen-bonding (RAHB) model [Gilli, Bellucci, Ferretti & Bertolasi (1989). J. Am. Chem. Soc. 111. 1023-1028; Bertolasi, Gilli, Ferretti & Gilli (1991). J. Am. Chem. Soc. 113, 4917-4925]. When the intramolecular hydrogen bond is forbidden for steric reasons, molecules crystallize by forming hydrogen-bonded infinite chains of pi-delocalized enolone fragments (resonant beta-chains), i.e. they are hybrids of the canonical forms -OH...O=C-C=C-OH...O=C- =+OH...-O-C=C-C=+OH...-O-C=. The occurrence of beta-chains in 14 crystals of enolone (2-en-3-ol-1-one) and eight of enediolone (2-en-2,3-diol-1-one) derivatives has been studied. The beta-chains were found to have the following properties: (i) O...O distances depend on the enediolone substituents and range from 2.69 angstrom in beta-ketoesters to 2.46 angstrom in beta-diketones; (iii) calculated hydrogen-bond energies are in the range 20-66 kJ mol-1; (iii) a strict intercorrelation between hydrogen-bond strengthening and pi-system delocalization is observed, in complete agreement with the RAHB model proposed previously. Beta-Chain morphologies are analyzed with the aim of determining crystal-engineering rules for the production of solid materials where systems of polar beta-chains can induce ferroelectric and second harmonic generation properties. The RAHB concept is generalized to other heteroconjugated systems such as carboxylic acids, amides, enamines (RN=CR-NHR) and enaminones (O=CR-CR=CR-NHR), and its possible relevance in biological processes such as base coupling in DNA and folding of proteins is briefly discussed
Evidence for Intramolecular N-H...O Resonance-Asssisted Hydrogen Bonding in Beta-Enaminones and Related Heterodienes. A Combined Crystal-Structures, IR and NMR Spectroscopic, and Quantum-Mechanical Investigation
No full textThe resonance-assisted hydrogen bond (RAHB) is a model of synergistic interplay between pi -delocalization and hydrogen-bond (H-bond) strengthening originally introduced (Gilli, G.; Bellucci, F.; Ferretti, V.; Bertolasi, V. J. Am. Chem. Sec. 1989, 111, 1023; Bertolasi, V.; Gilli, P.; Ferretti, V.1 Gilli, G. J. Aln. Chem. Sec. 1991, 113, 4917) for explaining the abnormally strong intramolecular O-H...O bonds formed by the ...O=C-C=C-OH... beta -enolone fragment I which are typical of B-diketone enols. The applicability of this model to the intramolecular N-H...O hydrogen bonds formed by a number of heteroconjugated systems (...O=C-C=C-NH..., beta -enaminones II; O=C-C=N-NH..., ketohydrazones III; and ...O=N-C=C-NH..., nitrosoenamines IV) is investigated. The X-ray crystal structures of five molecules which close a six-membered ring by an intramolecular N-H...O bond through the resonant ...O=X-C=X-NH... (X = C, N) fragments II-IV are compared to those of two other molecules closing the same ring through the nonresonant ...O=C-C-C-NH... beta -aminone moiety V. Experimental findings are complemented by a CSD (Cambridge Structural Database) search of all compounds forming intramolecular N-H...O bonds through the molecular fragments II-V and by a comprehensive analysis of the IR v(NH) stretching frequencies and H-1 NMR delta (NH) chemical shifts available for compounds of these classes of known crystal structure. It is shown that all the descriptors of H-bond strength [d(N...O) shorthening, decrease of v(NH), increase of delta (NH), and increase of pi -delocalization within the heteroconjugated fragment] are mutually intercorrelated according to RAHB rules, which can then account for the strength of heteronuclear N-H...O bonds in II-IV as well as for that of the homonuclear O-H...O bonds in I. Heteronuclear N-H...O bonds appear, however, to have distinctive features. In particular, their strength turns out to be partially hampered by the proton affinity difference (BPA) between the N and O atoms, so that very strong H-bonds (2.65 greater than or equal to d(N...O) greater than or equal to 2.48 Angstrom, 3200 greater than or equal to v(NH) greater than or equal to 2340 cm(-1), 13 less than or equal to delta (NH) less than or equal to 18 ppm) can occur only when the pi -delocalization of the heterodienic moiety is associated with proper electron-attracting substituents which are able to decrease this Delta PA by increasing the NH acidity. Moreover, at variance with strong O-H...O RAHBs, whose protons are mostly found in nearly symmetrical positions, even the strongest N-H...O RAHBs are highly dissymmetric, despite the very similar changes undergone by both IR and H-1 NMR spectra in O-H...O and N-H...O H-bonded systems. Specificities of heteronuclear H-bonds are shown to be interpretable by the electrostatic-covalent H-bond model (ECHBM) which was previously developed for the homonuclear case (Gilli, P.; Bertolasi, V.; Ferretti, V.; Gilli, C. J. Am. Chem. Sec. 1994, 116, 909). The conclusions drawn are corroborated by extended DFT quantum-mechanical calculations at the B3LYP/6-31+G(d,p)B3LYP/6-31+G(d,p) level of theory and by full geometry optimization carried out on 27 variously substituted heterodienes II-IV and nonresonant beta -aminones v. calculations allow the estimation of H-bond energies that are found to be approximately 2.75 kcal mol(-1) for nonresonant V and 5.22, 6.12, and 7.03 kcal mol(-1) for unsubstituted resonant II, III, and IV, respectively
Out-of-plane deformation pathways of the R(X=)C-NR2 fragment present in amides, thioamides, amidines, enamines, and anilines. A concerted study making use of structural data, molecular mechanics, and ab initio calculations
No full textThe R(X=)C-NR(1)R(2) (R(1), R(2) = alkyl groups) fragment is present in many classes of molecules and assumes, usually, a planar conformation owing to the C-N partial double-bond character. It can undergo,however, a cis-trans isomerization process by rotation around the C-N bond and concomitant nitrogen pyramidalization. In a previous paper (Gilli, G.; Bertolasi, V.; Bellucci, F.; Ferretti, V. J. Am. Chem. Sec. 1986, 108, 2420) the isomerization pathway was mapped by the use of some 90 crystal structures containing the fragment of interest, and a semiempirical potential giving the total energy of the fragment during its deformation was proposed. In the present work the previous sample of crystal structures is updated to the current state of the crystallographic databases; the observed geometries are compared with the out-of-plane deformation energy maps obtained by ab initio SCF calculations at the 4-31G level for sample molecules (thioformamide, formamide, formamidine, vinylamine, and aniline) representative of the five chemical classes investigated. It is shown that the originally proposed potential is validated by this analysis and that the values of the energetic barriers involved in the reaction, evaluated from the ab initio energy maps, are in good agreement with the available experimental data. It is found, moreover, that there is a specific class of compounds (o- and p-nitroanilines and polyconjugated enamines and amidines) which deviate from the general behavior. The crystal structures of two of these compounds are reported, and possible reasons for the discrepancies discussed
Evidence for Resonance-Assisted Hydrogen Bonding. 2.1Intercorrelation between Crystal Structure and Spectroscopic Parameters in Eight Intramolecularly Hydrogen Bonded 1,3-Diary 1–1,3-propanedione Enols
No full textCrystal structure analysis of eight 1,3-diaryl-1,3-propanedione enols has been accomplished with the aim of investigating in more detail the intramolecular hydrogen bond formed by the H-C=C-C=O fragment characterizing beta-diketone enols; structural data were correlated with spectroscopic parameters, that is IR nu(OH) stretching frequencies and H-1 NMR chemical shifts of the enolic proton. Present experimental data show that this hydrogen bond is characterized by the following interrelated features: (i) very short O- -O distances (2.432-2.554 angstrom); (ii) strong delocalization in the heteroconjugated fragment; (iii) lengthening of the O-H bond (to 1.20 angstrom); (iv) lowering of the nu(OH) frequencies (2566-2675 cm-1) and downfield shift of the enolic proton resonance (15.3-17.0 ppm). The data can bc interpreted by (and are in support of) the RAHB (resonance assisted hydrogen bond) model previously suggested (Gilli, G.; Bellucci, F.; Ferretti, V.; Bertolasi, V. J. Am. Chem. Soc. 1989, 111, 1023) for explaining the unusual features the hydrogen bond displays in these compounds. It is shown that the model is able to interpret fine structural details such as the general weakening of the intramolecular hydrogen bond caused by electron-donating 1,3-substituents or additional hydrogen bonds accepted by the carbonyl and the preference displayed by the proton for dwelling on the carbonyl oxygen having the smaller negative charge induced both by the nature of 1,3-substituents or by intermolecular hydrogen bonds or short contacts
Novel Olefin Metathesis Ruthenium Catalysts Bearing Backbone- Substituted Unsymmetrical NHC Ligands
No full textStable Ru-based catalysts containing unsym-
metrical N-heterocyclic carbene (NHC) ligands with phenyl
substituents on the backbone in syn and anti stereochemical
relationships have been easily prepared and fully characterized.
Preliminary investigation revealed that, depending on the
backbone configuration, the new Ru complexes displayed
different catalytic behaviors in representative olefin metathesis
reactions
INTRAMOLECULAR N-H...O=C HYDROGEN-BONDING ASSISTED BY RESONANCE - INTERCORRELATION BETWEEN STRUCTURAL AND SPECTROSCOPIC DATA FOR 6 BETA-DIKETO-ARYLHYDRAZONES DERIVED FROM BENZOYLACETONE OR ACETYLACETONE
No full textCrystal structure determinations of six beta-diketo-arylhydrazones have been accomplished with the aim of a detailed investigation of the nature of the intramolecular hydrogen bond formed by the HN-N=C-C=O fragment in these compounds. The N...O hydrogen bond distances are found to be correlated with the values of the spectroscopic parameters, i.e. IR nu(NH) stretching frequencies, H-1 NMR chemical shifts, lambda(max) of the UV absorption of the charge-transfer (CT) band from the hydrazone to the carbonyl group, and the Hammett constants, sigma(X), of the substituent X on the N-phenyl group. Experiments show that the hydrogen bond is characterized by the following interrelated features: ((i) very short N...O distances (2.551-2.600 angstrom); (ii) strong delocalization in the keto-hydrazone fragment; (iii) lowering of the nu(NH) frequencies (3002-3117 cm-1); (iv) H-1 NMR downfield shift of the proton resonance (14.53-14.93 ppm); and (v) UV lambda(max)(CT) in the range 370-406 nm. These findings are interpreted in terms of the RAHB (Resonance-Assisted Hydrogen Bonding) model [Gilli G., Bellucci F., Ferretti V., Bertolasi V., J. Am. Chem. Soc., 1989, 111, 1023]. We show that the magnitude of the strong hydrogen bond is essentially determined by the degree of pi-delocalization within the keto-hydrazone heteroconjugated system and modulated by all others factors that can affect the degree of pi-conjugation, including inductive effects and non-bonded intermolecular interactions
Software per analizzare le interazioni di gruppo: Cyram NetMiner e Ucinet
No full textPresentazione, esplorazione e confronto tra due strumenti software utili per Social Network Analysis (l’analizzi di interazioni all’interno di comunità virtuali): Cyram NetMinere e Ucinet
STRUCTURE AND CRYSTAL PACKING OF THE ORGANIC SALT 2-(DIMETHYLAMINO)-5-METHYL-1,3-THIAZOLIUM 1,1,2,3,3-PENTACYANOPROPENIDE, C6H11N2S+.C8N5-
No full text--
Tautomerism in bis(oxazolines): an experimental and theoretical study of proton transfer in 1,1-bis(4,4-dimethyl-1,3-oxazolin-2-yl)-ethane
No full textThe serendipitous isolation of an unusual protonated bis(oxazoline) prompted us to discuss the role of H+
on the kinetics and thermodynamics of the equilibrium between its ketimine and enamine forms. X-ray
diffraction analysis revealed that the protonated bis(oxazoline) is in the Z-enamine form, the unipositive
charge is counterbalanced by [(FeCl3)2O]2- and [FeCl4]- anions. DFT calculation at the BP86/TZVP level
showed that relative stability of enamine tautomer versus ketimine tautomer increases with the proton-
ation of the nitrogen atom of the oxazolidine ring. At the same time, the barrier energy of tautomerism
decreases
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