Showing papers on "Intramolecular force published in 1982"
TL;DR: In this article, ultrarapid (i.e., sub-picosecond) temporal evolution occurs by highly nonstatistical intramolecular rate processes in benzene and related polyatomic molecules.
Abstract: Ultrasensitive dye laser photoacoustic spectra have been obtained for CH and CD stretch overtone excitations of gas phase benzene (C6H6, C6D6, C6HD5), toluene, and fluorobenzenes (C6H5F, C6HF5) in the visible and near infrared spectral regions. Interpretations of the spectral observables (band positions, intensities, and widths) clarify the nature and dynamics of highly vibrationally excited states in benzene and related polyatomic molecules: (1) the states we initially prepare by direct one‐photon absorption involve highly localized and selective excitations of CH (CD) bond mode sites; (2) these localized excitations cause dynamical symmetry lowering of the molecular systems; and (3) ultrarapid (i.e., subpicosecond) temporal evolution occurs by highly nonstatistical intramolecular rate processes. Analyses of the energy and state dependence of overtone bandwidths support a mechanistic picture in which sequential state‐to‐state decays are the preferred dynamical pathways for intramolecular vibrational energy redistribution.
291 citations
TL;DR: In this paper, an asymmetric double minimum potential with an energy difference ΔG = 1.0 kJ/mol and an activation energy of Ea = 4.8 kj/mol between the two tautomeric forms is found.
Abstract: Direct evidence for dynamic intramolecular double proton exchange in carboxylic acid dimers in the solid is obtained from NMR measurements. For the p‐toluic acid dimer, an asymmetric double minimum potential with an energy difference ΔG = 1.0 kJ/mol and an activation energy of Ea = 4.8 kJ/mol between the two tautomeric forms is found. The equilibrium position of the carboxylic proton pair at low temperature is derived from the corresponding dipolar coupling tensor. The importance of double proton tunneling at low temperature is discussed.
204 citations
TL;DR: An extension of the nomenclature for classifying ring closures to include intramolecular reactions of enolate anions is described, and the rules governing such cyclizations are enumerated as discussed by the authors.
201 citations
190 citations
TL;DR: On DDQ under anhydrous conditions, hydroxy groups located at α or β position to methoxybenzyl ether groups were readily protected by the intramolecular oxidative formation of acid-sensitive methoxy benzylidene acetals, which were further oxidized to alkali-sensitive hydroxy esters in the presence of H 2 O as mentioned in this paper.
161 citations
TL;DR: In this article, a detailed analysis of the magnetic resonance (n.m.r.) properties of sucrose, using both D 2 O and dimethyl sulfoxide-d 6 as solvents, based on measurements of coupling constants, chemical shifts, T 1 relaxation times, and nuclear Overhauser enhancements.
157 citations
TL;DR: The crystal structure of bovine pancreatic ribonuclease-A has been refined by restrained least-squares analysis employing X-ray diffractometer data to 1.45/k resolution.
Abstract: The crystal structure of bovine pancreatic ribonuclease-A has been refined by restrained least-squares analysis employing X-ray diffractometer data to 1.45/k resolution. The current R factor for 19 238 reflections is 0.26 and 0.24 for 17 427 reflections with I(hkl) > 0. The r.m.s, deviation from ideality of bond lengths is 0.01A. Corrections, mostly of minor character, to previous models of the secondary structure have been made and a quantitative analysis of intramolecular hydrogen bonds is given. A total of 79 solvent molecules have been clearly identified in the first coordination sphere around the enzyme molecule and included in the least-squares analysis. A sulphate anion occurs in the active site and has also been refined as part of the structure. Further new features of the structure to emerge are: alternative sites for the His-119 side group with occupancies, refined in the analysis, of 0.80 and 0.20 respectively; a solvent molecule hydrogen bonded to the N-terminal amino group; and extensive disorder of the side chains in the region of residues 35-39. The r.m.s, deviation in atomic position between the current model and the starting model is 1-1 ./~ including some shifts of 7-8/k where major rebuilding of side groups was necessary.
151 citations
150 citations
147 citations
TL;DR: The oxidation-reduction potentials involved in the transfer are such that the process may be important in the mode of action of enzymes such as high-potential copper proteins and peroxidases, and perhaps also in the Mode of Action of other proteins if the environment is suitable.
139 citations
TL;DR: In this paper, the authors investigated the role of the solvent in intramolecular charge transfer processes, and in particular, the origin of the well-known dual fluorescence phenomena of pdimethylamino benzonitrile (DMABM) in mixed polar/nonpolar solutions.
Abstract: To probe the role of the solvent in intramolecular charge transfer processes, and in particular, the origin of the well‐known dual fluorescence phenomena of p‐dimethylamino benzonitrile (DMABM), picosecond laser studies in mixed polar/nonpolar solutions were undertaken. The anomalous long wavelength emission is attributed to a complex formed between excited DMABN and butanol with a rate constant of (9.7±1.5)×108 M−1 s−1. The dominant stabilization of the twisted intramolecular charge transfer state is therefore concluded to be due to a short range specific interaction with a polar solvent molecule. A secondary solvent effect arises from a further stabilization of the complex by long range polarization interactions with solvent molecules. Evidence on the existence of ground state complexes between DMABN and butanol are also presented. Excitation of these ground state complexes leads to the rapid formation of the excited state complexes in 30 ps, which we have interpreted to be the time required for the com...
TL;DR: In this paper, a hetero Diels-Alder route to 5,6-dihydro-γ-pyridones is described, where the imino linkage is exploited.
TL;DR: The protein structure is given in terms of symmetry or asymmetry in the polypeptide folding, Fe-S cluster ligation, charge distribution, and hydration by the water structure, and the intramolecular (hydrogen-bonding) and intermolecular interactions are summarized.
TL;DR: In this paper, a realistic molecular model was constructed and analyzed for intramolecular vibrational relaxation of CH overtones in benzene, and calculated overtone lineshapes were in good agreement with experiment.
Journal Article•
TL;DR: In this article, the dominant part of the neutral-to-ionic transition in a tetrathiafulvalene-p-chloranil (TTFCA) single crystal over the temperature range from 2 K to room temperature was investigated and it was shown that the transition occurs in a temperature range of about 30 K in width.
TL;DR: In this paper, the authors measured the rate constants kHHH, kHHD, kHDD, kDHD and kDDD for symmetric double proton-transfer reactions.
Abstract: Double proton-transfer reactions are characterized by three primary kinetic H/D isotope effects (k.i.e.) involving a set of rate constants kHH, kHD, kDH and kDD. We have succeeded in measuring such sets for well defined symmetrical double proton-transfer reactions where kHD=kDH for the intramolecular hydrogen migration in meso-tetraphenylporphine (TPP) and for the intermolecular 1 : 1 proton exchange between acetic acid and methanol dissolved in tetrahydrofuran. In this system we also detected a triple proton transfer involving one methanol and two acetic acid molecules. Rate constants kHHH, kHHD, kHDD and kDDD of this reaction are reported. Additionally, we also observed an intramolecular double proton-transfer reaction in 2,5-dianilino-benzoquinone- 1,4-dianil (azophenine, AP) for which we have measured the HH/HD k.i.e. For the determination of rate constants dynamic n.m.r. spectroscopy was used.The predictions of the fractionation-factor theory, transition-state theory and different proton-tunnelling theories on the HH/HD/DH/DD k.i.e. of symmetrical double proton-transfer reactions are discussed with special emphasis on the rule of the geometric mean and compared with the experiments. The kinetic and the i.r. results for TPP and AP are well reproduced by the vibrational model of tunnelling as proposed previously by us. TPP is, therefore, the first proton-transfer system with NH-stretching levels not broadened by hydrogen-bond effects. The k.i.e. of the intermolecular proton exchange in the system acetic acid + methanol + tetrahydrofuran are consistent with tunnelling from the OH-stretching ground states. The energy of activation is associated with the enthalpy of formation of the cyclic complex in which the exchange takes place and the excited intermolecular vibrational states within this complex. The tunnelling theories are modified in order to take this enthalpy into account.
TL;DR: In this article, the dynamics of a collection of seven Morse or harmonic oscillators were investigated to model a molecule in which two halves are separated by a heavy atom, and the results were related to a recent experiment on intramolecular dynamics and suggest an extension of the anharmonic local mode concept to groups.
TL;DR: In this article, the first synthesis of a metal complex containing the (12)ane-P/sub 3/ triphosphine macrocycle was reported, which is an example of a reaction which takes advantage of a kinetic template effect.
Abstract: This communication reports the first synthesis of a metal complex containing the (12)ane-P/sub 3/ triphosphine macrocycle (HPCH/sub 2/CH/sub 2/CH/sub 2/)/sub 3/. This reaction is an example of a reaction which takes advantage of a kinetic template effect. The reaction exemplifies the kinetic template effect since uncoordinated allylphosphine when treated with AIBN yields entirely different products. The reaction is clean, resulting in only slight molybdenum carbonyl complex degradation and no evidence for intramolecular ring closure to form coordinated phosphabutane rings or intermolecular P-H bond addition. The reaction is highly regiospecific; no Morkovnikov addition product has been detected. Studies of the generality of this metal-templated cyclization approach, derivatization of the hydridomacrocycles complexes, and displacement of the macrocyclic phosphine from the metal are in progress currently.