Acid-catalyzed hydrolysis of 4-diazo-3-isochromanone: the effect of coplanarity on the carbon protonation of α-phenyl-α-carbonyldiazo compounds

1996 ◽  
Vol 74 (7) ◽  
pp. 1369-1372 ◽  
Author(s):  
E.A. Jefferson ◽  
A.J. Kresge ◽  
S.W. Paine
Keyword(s):  
Carbon Atom ◽  
Negative Charge ◽  
Diazo Compound ◽  
Cyclic Compound ◽  
Phenyl Group ◽  
Molecular Orbital Calculations ◽  
Am1 Calculations ◽  
Charge Delocalization ◽  
Acyclic Analog ◽  
Hydrolysis Of

Hydrolysis of the cyclic α-phenyl-α-carbonyl-diazo compound, 4-diazo-3-isochromanone, in dilute aqueous perchloric acid solutions was found to give the hydronium ion isotope effect [Formula: see text] which shows that this reaction occurs by rate-determining hydronation of the substrate on the carbon atom α to its diazo group. Comparison of the rate constant obtained, [Formula: see text] with that for the corresponding acyclic analog, methyl phenyldiazoacetate, indicates that the cyclic compound is 57 times less reactive. Semi-empirical AM1 molecular orbital calculations suggest that this difference in reactivity is caused by enforced near-coplanarity of the diazo and phenyl groups in the cyclic substrate, as opposed to a staggered arrangement of these groups in the acyclic analog; this coplanarity then enhances delocalization of negative charge from the diazo α-carbon atom into the phenyl group, which reduces the negative charge density on the α-carbon atom and slows the rate of reaction. Key words: hydrolysis, diazoalkanes, charge delocalization, AM1 calculations.

Acid-catalyzed hydrolysis of 4-diazo-isothiochroman-3-one. Comparison with the acyclic analog and the corresponding oxygen system

1997 ◽  
Vol 75 (1) ◽  
pp. 56-59 ◽  
Author(s):  
E.A. Jefferson ◽  
A.J. Kresge ◽  
S.W. Paine
Keyword(s):  
Carbon Atom ◽  
Negative Charge ◽  
Molecular Orbital Calculations ◽  
Am1 Calculations ◽  
Charge Delocalization ◽  
Rate Determining Step ◽  
Hydronium Ion ◽  
Acid Catalyzed ◽  
Group Migration ◽  
Hydrolysis Of

The acid-catalyzed hydrolysis of the cyclic diazothiolactone, 4-diazoisochroman-3-one (3) was found to occur with the hydronium-ion isotope effect, [Formula: see text] and to give the ring-contracted product, 1,3-dihydrobenzo[c]thiophene-1-carboxylic acid (4). This shows that protonation of the diazo carbon atom occurs in the rate-determining step and that the reaction also involves migration of the thio group. The hydronium-ion catalytic coefficient for this reaction, [Formula: see text], is 45 times less than that for hydrolysis of its acyclic thio ester analog, S-methyl phenyldiazothioacetate (5). Semiempirical AM1 molecular orbital calculations support the idea that this difference in reactivity is the result of increased delocalization of negative charge into the aromatic ring in the case of the cyclic substrate, which reduces the negative charge on the diazo carbon atom and makes it less susceptible to protonation. Key words: hydrolysis, diazoalkanes, charge delocalization, AM1 calculations, thio group migration.

scholarly journals Zerumbone Inhibits Helicobacter pylori Urease Activity

Molecules ◽  
2021 ◽  
Vol 26 (9) ◽  
pp. 2663
Author(s):  
Hyun Jun Woo ◽  
Ji Yeong Yang ◽  
Pyeongjae Lee ◽  
Jong-Bae Kim ◽  
Sa-Hyun Kim
Keyword(s):  
Helicobacter Pylori ◽  
Carbon Atom ◽  
Natural Compound ◽  
Urease Activity ◽  
Negative Charge ◽  
Positive Charge ◽  
Gastric Epithelium ◽  
Functional Inhibition ◽  
Electrical Gradient ◽  
H Pylori

Helicobacter pylori (H. pylori) produces urease in order to improve its settlement and growth in the human gastric epithelium. Urease inhibitors likely represent potentially powerful therapeutics for treating H. pylori; however, their instability and toxicity have proven problematic in human clinical trials. In this study, we investigate the ability of a natural compound extracted from Zingiber zerumbet Smith, zerumbone, to inhibit the urease activity of H. pylori by formation of urease dimers, trimers, or tetramers. As an oxygen atom possesses stronger electronegativity than the first carbon atom bonded to it, in the zerumbone structure, the neighboring second carbon atom shows a relatively negative charge (δ−) and the next carbon atom shows a positive charge (δ+), sequentially. Due to this electrical gradient, it is possible that H. pylori urease with its negative charges (such as thiol radicals) might bind to the β-position carbon of zerumbone. Our results show that zerumbone dimerized, trimerized, or tetramerized with both H. pylori urease A and urease B molecules, and that this formation of complex inhibited H. pylori urease activity. Although zerumbone did not affect either gene transcription or the protein expression of urease A and urease B, our study demonstrated that zerumbone could effectively dimerize with both urease molecules and caused significant functional inhibition of urease activity. In short, our findings suggest that zerumbone may be an effective H. pylori urease inhibitor that may be suitable for therapeutic use in humans.

Impact of negative charge delocalization on the properties of solid polymer electrolytes

2021 ◽  
Author(s):  
Heng Zhang ◽  
Ziyu Song ◽  
Weimin Yuan ◽  
Wenfang Feng ◽  
Jin Nie ◽  
...  
Keyword(s):  
Polymer Electrolytes ◽  
Negative Charge ◽  
Solid Polymer Electrolytes ◽  
Solid Polymer ◽  
Charge Delocalization

ChemInform Abstract: Formation of a Phosphobetaine with Negative Charge at the δ-Carbon Atom of the 1,3-Butadienyl Group by Reaction of Tributylphosphine with Vinylacetylene.

ChemInform ◽  
1987 ◽  
Vol 18 (6) ◽  
Author(s):  
G. TS. GASPARYAN ◽  
S. K. BARSEGYAN ◽  
M. ZH. OVAKIMYAN ◽  
P. V. PETROVSKII ◽  
M. G. INDZHIKYAN
Keyword(s):  
Carbon Atom ◽  
Negative Charge

Theoretical investigation on tautomerism and NLO properties of Salicylideneaniline derivatives

2021 ◽  
Author(s):  
N. Daho ◽  
N. Benhalima ◽  
F. KHELFAOUI ◽  
O. SADOUKI ◽  
M. Elkeurti ◽  
...  
Keyword(s):  
Optical Properties ◽  
Density Functional ◽  
Energy Gap ◽  
Intramolecular Proton Transfer ◽  
Basis Set ◽  
Frontier Molecular Orbital ◽  
Molecular Orbital Calculations ◽  
Visible Absorption ◽  
Charge Delocalization ◽  
Intramolecular Hydrogen

In this work, a comprehensive investigation of the salicylideneaniline derivatives is carried out using density functional theory to determine their linear and non-linear optical properties. Geometry optimizations, for gas and solvent phases, of the tautomers (enol and keto forms) are calculated using B3LYP levels with 6–31G (d,p) basis set . An intramolecular proton transfer, for 1SA-E and 2SA-E, is performed by a PES scan process at the B3LYP/6-31G (d,p) level. The optical properties are determined and show that they have extremely high nonlinear optical properties. In addition, the RDG analysis, MEP, and gap energy are calculated. The low energy gap value indicates the possibility of intramolecular charge transfer. The frontier molecular orbital calculations clearly show the inverse relationship of HOMO–LUMO gap with the first-order hyperpolarizability (β = 59.6471 × 10-30 esu), confirming that the salicylideneaniline derivatives can be used as attractive future NLO materials. Therefore, the reactive sites are predicted using MEP and the visible absorption maxima are analyzed using a theoretical UV–Vis spectrum. Natural bond orbitals are used to investigate the stability, charge delocalization, and intramolecular hydrogen bond.

176. Mechanism of substitution at a saturated carbon atom. Part XI. Hydrolysis of tert.-butyl bromide in acidic moist acetone

1940 ◽  
pp. 913 ◽  
Author(s):  
Leslie C. Bateman ◽  
Kenneth A. Cooper ◽  
Edward D. Hughes
Keyword(s):  
Carbon Atom ◽  
Butyl Bromide ◽  
Tert Butyl ◽  
Hydrolysis Of ◽  
Saturated Carbon Atom

scholarly journals NHC Core Pincer Ligands Exhibiting Two Anionic Coordinating Extremities

Molecules ◽  
2020 ◽  
Vol 25 (9) ◽  
pp. 2231 ◽  
Author(s):  
Rachid Taakili ◽  
Yves Canac
Keyword(s):  
Carbon Atom ◽  
Negative Charge ◽  
Synthetic Methods ◽  
Pincer Ligands ◽  
Chemical Behavior ◽  
Coordination Properties

The chemistry of NHC core pincer ligands of LX2 type bearing two pending arms, identical or not, whose coordinating center is anionic in nature, is here reviewed. In this family, the negative charge of the coordinating atoms can be brought either by a carbon atom via a phosphonium ylide (R3P+–CR2−) or by a heteroatom through amide (R2N−), oxide (RO−), or thio(seleno)oxide (RS−, RSe−) donor functionalities. Through selected examples, the synthetic methods, coordination properties, and applications of such tridentate systems are described. Particular emphasis is placed on the role of the donor ends in the chemical behavior of these species.

Studies in Solvolysis. Part VII. The Neutral Hydrolysis of Methyl Perchlorate

1975 ◽  
Vol 53 (20) ◽  
pp. 3106-3115 ◽  
Author(s):  
Ross Elmore Robertson ◽  
Adrianna Annesa ◽  
John Marshall William Scott
Keyword(s):  
Heat Capacity ◽  
Carbon Atom ◽  
Temperature Dependence ◽  
Thermodynamic Parameters ◽  
Isotope Effect ◽  
Perchlorate Ion ◽  
Rate Of Hydrolysis ◽  
Leaving Groups ◽  
Hydrolysis Of

The temperature dependence of the rate of hydrolysis of methyl perchlorate has been measured and the entropy (ΔS≠), enthalpy (ΔH≠), and heat capacity (ΔCp≠) of activation calculated. The measurements confirm that the perchlorate ion is superior to all other leaving groups in water. The isotope effect related to the hydrolysis of methyl-d3 perchlorate has been measured at three temperatures and shown to be inverse. The thermodynamic parameters and the isotope effect were examined with respect to the mechanism of substitution at a primary carbon atom.

scholarly journals Rate limiting P-O(5') bond cleavage of RNA fragment: ab initio molecular orbital calculations on the base-catalyzed hydrolysis of phosphate

1991 ◽  
Vol 19 (10) ◽  
pp. 2747-2753 ◽  
Author(s):  
K. Taira ◽  
T. Uchimaru ◽  
K. Tanabe ◽  
M. Uebayasi ◽  
S. Nishikawa
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Bond Cleavage ◽  
Molecular Orbital Calculations ◽  
Rate Limiting ◽  
Hydrolysis Of

scholarly journals Comparative studies of the specificities of α-chymotrypsin and subtilisin BPN′. Studies with flexible and ‘locked’ substrates

1972 ◽  
Vol 126 (3) ◽  
pp. 659-665 ◽  
Author(s):  
T. N. Pattabiraman ◽  
W. B. Lawson
Keyword(s):  
Methyl Ester ◽  
Carbon Atom ◽  
Binding Site ◽  
Comparative Studies ◽  
Detrimental Effect ◽  
Optically Active ◽  
The Other ◽  
Optical Isomers ◽  
Polar Groups ◽  
Hydrolysis Of

Subtilisin BPN′ hydrolysed N-acetyl-l-3-(2-naphthyl)-alanine methyl ester, N-acetyl-l-leucine methyl ester and N-acetyl-l-valine methyl ester, faster than α-chymotrypsin. Of eight ‘locked’ substrates tested, only methyl 5,6-benzindan-2-carboxylate was hydrolysed faster by subtilisin, whereas the other esters were better substrates for chymotrypsin. Compared with the values for chymotrypsin, the stereospecific ratios during the hydrolysis of the optically active locked substrates by subtilisin were decreased by one and two orders of magnitude for bi- and tri-cyclic substrates respectively. The polar groups adjacent to the α-carbon atom of locked substrates did not contribute significantly to the reactivity of the more active optical isomers, but had a detrimental effect on the less active antipodes during hydrolysis by both the enzymes. These studies show that the binding site of subtilisin BPN′ is longer and broader than that of α-chymotrypsin.

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