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Topic: Deprotonation


In the News (Sun 26 May 19)

  
  Deprotonation - Wikipedia, the free encyclopedia
Deprotonation is a chemistry term that refers to the removal of a proton (hydrogen ion H
Where the proton is not particularly acidic, and as such, the molecule does not give up its proton easily, a base stronger than the commonly known hydroxides are required.
Hydrides are one of the many types of powerful deprotonating agents.
en.wikipedia.org /wiki/Deprotonation   (254 words)

  
 .: Research - Richard Research Group :.
Deprotonation of α-carbonyl carbon gives a delocalized "carbanion" where the negative charge lies mainly at the enolate oxygen that is derived from the neutral carbonyl oxygen at the substrate.
The deprotonation of the α-CH and α-CH OD groups of hydroxyacetone and the α-CH groups of acetone in the presence of acetate buffer and zinc chloride in D
provides 6.3 and 4.4 kcal/mol stabilizations, respectively, of the transition states for deprotonation of the α-CH OD and α-CH groups of hydroxyacetone by acetate anion (Scheme 2), and a smaller 3.3 kcal/mol stabilization of the transition state for deprotonation of the α-CH group of acetone.
www.acsu.buffalo.edu /~jrichard/r_hydride_tx.html   (558 words)

  
 Post Test: Protonation/Deprotonation Problems   (Site not responding. Last check: 2007-11-01)
The student was able to protonate and deprotonate functional groups and to indicate the correct charges, but was not able to decided which group was acidic and which was basic.
In this case, the student was able to protonate and deprotonate the correct groups and indicate the correct charges.
This was another example of where the student was able to protonate, deprotonate, and represent the correct charges, but was not able to decided where to protonate nd where to deprotonate.
www.umich.edu /~csie/undergraduate/jason/posttest/studentwork/PD   (152 words)

  
 Two Groups Control Light-Induced Schiff Base Deprotonation and the Proton Affinity of Asp85 in the Arg82His Mutant of ...
molecules in response to the deprotonation of the proton release
the pigment in response to the deprotonation of the proton release
The complex extracellular domain regulates the deprotonation and reprotonation of the retinal Schiff base during the bacteriorhodopsin photocycle.
www.biophysj.org /cgi/content/full/77/5/2750   (7015 words)

  
 C. Gatti, A. Ponti, A. Gamba and G. Pagani, J. Am. Chem. Soc., 114, 8634-8644 (1992)   (Site not responding. Last check: 2007-11-01)
The downfield shift of deprotonated nitrogens results from the dominance of the decrease in shielding in the molecular plane over the concurrent increase (or near constancy) of the out-of-plane shielding.
The charge density rearrangements occurring upon deprotonation are rationalized in terms of the relevant RHF/6-31G+ charge density topologies, within the framework of the quantum theory of atoms in molecules.
The a density made available upon deprotonation at nitrogen is to a great extent transferred to the whole molecular a framework.
www.istm.cnr.it /~ponti/JACS92.html   (327 words)

  
 Department of Chemistry: Seminar
Carbon deprotonation is the first step in chemical and biochemical syntheses of new carbon-carbon bonds, so that an understanding of the mechanism for this simple process has broad general relevance to Chemistry and Biology.
There is a good correlation between the rate constant for deprotonation of neutral a-carbonyl carbon by hydroxide ion and the pKa of the carbon acid.
The systematic deviations observed for the rate constants for deprotonation of nitriles, N-protonated derivatives of a-amino acids, and acetate anion from this linear relationship provide interesting insight onto the factors which control the kinetic barrier for proton transfer at carbon.
www.chemistry.mcmaster.ca /seminars/0001/chem.20010308.html   (182 words)

  
 JCE 1996 (73) 254 [Mar] The Effect of Solvent and Micelles on the Rate of Excited-State Deprotonation
In aqueous solution, the rate of excited-state deprotonation of the acid form of the ion is much faster than fluorescence and nonradiative decay.
In solvents with high ethanol content, the rate of excited-state deprotonation is much slower than that in aqueous solution and emission occurs mainly from the acid form of the ion.
In such solvents, HPTS exhibits a violet emission with a lambda max at 455 nm which is characteristic of the acid form of the ion.
jchemed.chem.wisc.edu /Journal/issues/1996/Mar/abs254.html   (396 words)

  
 Forming Enolates Under Non-Basic Conditions
The standard method of enolate generation is deprotonation of a carbon alpha to an electron-withdrawing group, where the electron-withdrawing group is anything from a carbonyl to a nitrile.
Deprotonation to form an enolate ion is done with a variety of bases, from hydroxide ion to hydride to lithium diisopropyl amide (LDA).
The acidity of the hydrogen in the alpha position is low (pKa range from 18-24, depending upon what is attached to the R position, as shown in Figure 1), so the hydrogen is moderately labile.
www.ux1.eiu.edu /~mdruane/RI2005a.html   (787 words)

  
 Deprotonation and Metal Chelation Studies of Sulphonated Morin   (Site not responding. Last check: 2007-11-01)
Sulphonation was performed to increase the water solubility of 1.
Analysis of potentiometric titration data resulted in the determination of four pKa's for the deprotonation of hydroxy groups in agreement with earlier reports.
Theoretical calculations were employed to predict the sequence for the deprotonations.
acs.confex.com /acs/56serm/techprogram/P12796.HTM   (187 words)

  
 Carbanions
Organic chemists are interested in generating nucleophilic carbon because the formation of carbon-carbon bonds lies at the heart of organic synthesis, and the vast majority of carbon-carbon bond forming reactions involve the coupling of a nucleophilic carbon with an electrophilic carbon.
Hence it is possible to deprotonate the methyl group using bases such as sodium amide or n-butyllithium.
Since alkanes are the weakest acids, it is not possible to generate their conjugate bases by deprotonation.
www.usm.maine.edu /~newton/Chy251_253/Lectures/Carbanions/Carbanions.html   (1330 words)

  
 Untitled Document   (Site not responding. Last check: 2007-11-01)
Small peptides ions consisting of a comparable number of amino acid residues but varying in composition and sequence were allowed to undergo gas-phase deprotonation reactions.
Rate constants were determined for the deprotonation reactions of the peptide ions with a series of reference compounds of known gas-phase basicities ranging from 190.0 to 232.6 kcal/mol.
All of the multiply charged peptide ions were sequentially deprotonated to the +1 charge state by ion/molecule reactions.
bama.ua.edu /~ccassady/abs3.html   (304 words)

  
 Alkylations
The success of the aldol condensation and the Claisen condensation depends upon the fact that the value of the equilibrium constant for deprotonation of a carbon atom adjacent to a carbonyl group is such that significant concentrations of nucleophilic and electrophilic carbons are present in the reaction mixture simultaneously:
While this reaction might look feasible on paper, the desired outcome is precluded by competition from both the aldol condensation and the Sn2 reaction shown in Equation 2.
In other words, nucleophilic aliphatic substitution competes with deprotonation; direct attack of the hydroxide ion on the methyl carbon of methyl bromide is preferred to attack at one of the methyl hydrogens of acetone.
www.usm.maine.edu /~newton/Chy251_253/Lectures/Alkylations/Alkylations.html   (989 words)

  
 SoS 1997 - A local density functional study on deprotonation   (Site not responding. Last check: 2007-11-01)
A local density functional study on the deprotonation of hexaaqua aluminum complex
Local density functional with a new dielectric screening model approach has been used to interpret the deprotonation reactions of hexaaqua aluminum complex in aqueous solutions.
Through LDF/COSMO calculations, the major deprotonation scheme corresponding to the experimental determination of first hydrolysis enthalpy can be figured out.
www.hintze-online.com /sos/1997/Articles/Art1   (115 words)

  
 OCOL Mechanisms & Animations   (Site not responding. Last check: 2007-11-01)
The Hofmann Rearrangement of amides to give amines follows a complex mechanism including an alkyl group migration and the decarboxylation of a carbamic acid.
The sequence begins with deprotonation of the amide nitrogen by base to give an anion, which reacts with bromine to give an N-bromo amide.
Deprotonation of this intermediate forms an anion which can expel bromide anion with the concurrent migration of the alkyl group from the carbonyl carbon to the nitrogen, yielding an alkyl isocyanate.
www.chem.uic.edu /web1/OCOL3/MECH/24_05.HTM   (122 words)

  
 Untitled Document   (Site not responding. Last check: 2007-11-01)
Ions were generated by electrospray ionization and studied in a Fourier transform ion cyclotron resonance mass spectrometer.
formed directly from the electrospray process, deprotonation reactions with ammonia and 2-fluoropyridine yield non-linear pseudo-first-order kinetic behavior that indicates the presence of two ion structures.
The fraction of ions that undergo the fastest deprotonation reactions, and is presumably the least energetically stable isomer, accounts for approximately 60% of the [M+12H]
bama.ua.edu /~ccassady/abs9.html   (209 words)

  
 [No title]
Deprotonated negative ions are considered as deprotonated acidic sites, therefore, "acidic" prefix is used for them.
To further understand the difference between micro and macro constants we consider ionization equilibrium of a triprotic acid AH Referring to the different deprotonation sites of the AH molecule we introduce the upper indexes of the protons.
) > 0 than deprotonation of amide/imide is favored and it it said to have an acidic character.
www.chemaxon.com /marvin/chemaxon/marvin/help/pKa.html   (705 words)

  
 Pyridyl Group Assisted Deprotonation of a Methyl Group on Silicon: Complex Induced Proximity Effect and Novel ...
It was found that the deprotonation (t-BuLi/Et C) occurs with 2-pyridyltrimethylsilane but not with other related silanes such as phenyltrimethylsilane, 3-pyridyltrimethylsilane, and 4-pyridyltrimethylsilane.
It seems that this deprotonation proceeded through the agency of the complex-induced proximity effect (CIPE) of a 2-pyridyl group on silicon.
H NMR analysis of (2-pyridyldimethylsilyl)methyllithium revealed the intramolecular coordination of a pyridyl group to lithium.
pubs.acs.org /cgi-bin/abstract.cgi/joceah/2001/66/i11/abs/jo015528g.html   (219 words)

  
 Stepwise Hydration, and Multi-Body Deprotonation with Steep Negative Temperature Dependence, in the Benzene•+ - Water ...   (Site not responding. Last check: 2007-11-01)
In this work, we studied the stepwise hydration and solvent-mediated deprotonation of the Benzene
We observed a remarkable sudden decrease in the entropy of association accompanying the formation of Bz and Bz indicating strong orientational restraint in the hydration shells of these clusters consistent with the formation of cage-like structures.
We observed the size-dependent deprotonation of Bz in a cooperative multi-body process, where n H
acs.confex.com /acs/56serm/techprogram/P12984.HTM   (273 words)

  
 NSC Project 2004269
Chiral lithium amides are used in enantioselective deprotonation reactions, e.g.
DFT is a powerful tool that is known to generate accurate geometries and energies of equlibrium structures and activated complexes to a computational cost that makes it possible to investigate systems even of large size by using computer clusters with many nodes.
The computations that will be performed are geometry optimizations and frequency calculations of initial states and transition structures of the chiral lithium amide deprotonation.
www.nsc.liu.se /projects/previousprojects/project_2004269.html   (316 words)

  
 Ribozyme speed limits -- EMILSSON et al. 9 (8): 907 -- RNA
The apical bonds to the pentacoordinated phosphorous in the trigonal, bipyramidal structure are indicated with dotted lines.
Deprotonation of the 2'-oxygen nucleophile would be required in the lower pathway to prevent it from departing more readily than the 5'-oxygen atom.
The upper and lower pathways will be kinetically indistinguishable if deprotonation of the 2' oxygen in the neutral phosphorane is more rapid than cleavage of the P-O5' bond, and protonation also occurs at the 5' oxygen.
www.rnajournal.org /cgi/content/full/9/8/907   (6968 words)

  
 [No title]   (Site not responding. Last check: 2007-11-01)
We have shown that trivalent state of Cu and Ni is a reasonable oxidation state for biological redox reactions.Currently CV is used tostudy to Cu(II)-tetrapeptide and Cu(III)-tetrapeptide complex.
OSWV is used to determine the pKa of amine deprotonation for Cu(III) tri- and tetra- peptides.
Fredericks (Fredericks, F.C. Thesis, Purdue University, 1993) observed a decrease of pKa values of amine deprotonation as the reduction potential of the complex increases.
www.chem.purdue.edu /margerum/electro.html   (486 words)

  
 AEGiS-03CROI: pH dependence of HIV-1 protease inhibition by pyranones and 5,6-dihydropyranones: relevance to cellular ...
X-ray crystallographic structural data indicated the 4-hydroxyl group common to all the inhibitors (found to have a pKa of 4-5) is within hydrogen bonding distance of the two catalytic Asps of the protease.
Thus, it is possible that the loss of inhibitory activity at higher pH is due to deprotonation of the 4-hydroxyl group and loss of an important enzyme-inhibitor interaction.
The dihydropyranone was found to have a pKa=5.6, higher than that of the structurally similar pyranone.
www.aegis.com /conferences/CROI/1996/149.html   (384 words)

  
 Miami University Department of Chemistry and Biochemistry
Yan, Z. and Sebastian, J. F., "Density Functional Theory Investigation of the Deprotonation of Oxete", Tetrahedron Letters, 2002, 43, 8383-8386.
Power, T.D. and Sebastian, J.F., "Relative Anion Stabilities and Transition State Energies Regarding Vinylic vs Allylic Deprotonation of Cyclic Vinyl Ethers by Organolithium Reagents: An Ab Initio Study," Tetrahedron, 1998, 54, 8371-8392.
Power, T.D. and Sebastian, J.F., "Vinylic vs Allylic Deprotonation: An Ab Initio Molecular Orbital Study of 2,3-Dihydrooxepin and 1,3-Cycloheptadiene," Tetrahedron Letters, 1996, 37, 9127-9130.
www.cas.muohio.edu /chm/Faculty/Sebastian.htm   (424 words)

  
 SJU : The Chemistry Department
We are investigating the interdependence between the deprotonation of coordinated tripodal imidazolyl/benzimdazolyl ligands and the physical and chemical properties of a metal ion within the tripodal framework.
This study confirms that distal deprotonation of a coordinated benzimidazolyl ligand contained within an unsaturated Co(II) complex can be isolated and characterized.
) ligand systems that will be used to probe further the structure/function relationship of selective deprotonation as it relates to the chemical reactivity of small molecules.
www.sju.edu /cas/chemistry/bhammes/research.html   (1124 words)

  
 Stereoselective transformation of cyclodecene-1,4-dione systems, derived from steroids, to the corresponding ...
In this intermediate deprotonation involving its weakest (C(3)H) bond results in formation of the
However, upon deprotonation from the C(6) hydroxyl the spiro-
The above calculations indicate that intermediates C and F should be preferentially stabilized by C-deprotonation, involving hydrogen in the vicinity of the carbocationic site, thus producing compounds II and III in the (Z)-series and compounds VI and VII in the (E)-series.
www.chem.bg.ac.yu /~ijuranic/rad5.htm   (1324 words)

  
 SODIUM BOROHYDRIDE - Rohm and Haas Synthesis Technologies-Reducing Agents, Coupling Precursors, Borohydride, Hydride, ...   (Site not responding. Last check: 2007-11-01)
B(OCH3)3 is a precursor to Boronic acids and esters, used in Suzuki coupling chemistry - it is a cost-efficient alternative to Triisopropyl Borate.
Sodiumhydride, a 60% NaH dispersion in mineral oil, is used as a deprotonation agent in coupling chemistry, such as N-alkylation and C-C condensations.
Recent developments indicate the use of Boro-Hydride formulations for the generation of hydrogen as a carburant of Fuel Cells, the so-called Hydrogen On Demand (HOD) system.
www.rohmhaas.com /hydride   (171 words)

  
 Most Requested Documents 2Q 2001 - Chemistry and Related Science - CAS Science Spotlight   (Site not responding. Last check: 2007-11-01)
deprotonation studies on secondary and tertiary sulfonamides 1 and 2 using n-BuLi have been carried out.
conditions lead to ortho and benzylic deprotonation, resp.
Metalation of 1 using the n-BuLi/KOtBu superbase led to regioselective benzylic metalation (Figure 4); LDA deprotonation was also briefly explored.
www.cas.org /spotlight/rlist2q/200106j11.html   (157 words)

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