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Topic: Mesomeric effect


In the News (Sun 20 Apr 14)

  
  Mesomeric effect Encyclopedia   (Site not responding. Last check: 2007-10-26)
The mesomeric effect or resonance effect in chemistry is a property of substituents or functional groups in a chemical compound.
The effect is used in a qualitative way and describes the electron withdrawing or releasing properties of substituents based on relevant resonance structures and is symbolized by the letter M.
It's important to note that the mesomeric effect as a result of p - orbital overlap (resonance) has absolutely no effect on this inductive effect, as this effect is purely to do with the electronegativity of the atoms and their structural chemistry (which atoms are connected to which).
www.hallencyclopedia.com /topic/Mesomeric_effect.html   (317 words)

  
 Mesomeric effect
The Mesomeric effect is the effect of the overlap of a p-orbital with the p-orbital on an adjacent atom in the chemical compound to form a delocalised cloud of electrons over both the atoms called a π (pi) bond.
The effect is symbolized by M. The mesomeric effect of delocalised electrons occurs in unsaturated organic compounds, where the double bond is separated by a single bond.
It's important to note that the mesomeric affect as a result of p - orbital overlap has absolutely no affect on the inductive effect, as this effect is purely to do with the electronegativity of the atoms and their structural chemistry (which atoms are connected to which).
www.ibpassociation.org /encyclopedia/Chemistry/Mesomeric_effect.php   (305 words)

  
  Mesomeric effect at AllExperts
The mesomeric effect or resonance effect in chemistry is a property of substituents or functional groups in a chemical compound.
The effect is used in a qualitative way and describes the electron withdrawing or releasing properties of substituents based on relevant resonance structures and is symbolized by the letter M.
It's important to note that the mesomeric effect as a result of p - orbital overlap (resonance) has absolutely no effect on this inductive effect, as this effect is purely to do with the electronegativity of the atoms and their structural chemistry (which atoms are connected to which).
en.allexperts.com /e/m/me/mesomeric_effect.htm   (283 words)

  
 M
The effect (on reaction rates, ionization equilibria, etc.) attributed to a substituent due to overlap of its p or pi orbitals with the p or pi orbitals of the rest of the molecular entity.
The effect is symbolized by M. Strictly understood, the mesomeric effect operates in the ground electronic state of the molecule.
It is particularly useful to discuss structural effects on the transition state geometry for processes occurring either by stepwise or concerted routes.
www.chem.qmul.ac.uk /iupac/gtpoc/M.html   (2808 words)

  
 Electron Availability - Mesomeric Effects
A mesomeric effect is an electron redistribution that occurs via a pi orbital, quite often via conjugated systems.
There is an inductive effect (indicated by the arrow) in the "real" structure, but it is smaller than the mesomeric effect.
Mesomeric (and inductive) effects are permanent effects that are present in the ground state of the molecule.
www.everyscience.com /Chemistry/Organic/Electronic_and_Steric_Effects/b.1163.php   (306 words)

  
 Inductive effect at AllExperts
The Inductive effect in chemistry is an experimentally observable effect of the transmission of charge through a chain of atoms in a molecule by electrostatic induction (IUPAC definition).
The net polar effect exerted by a substituent is a combination of this inductive effect and the mesomeric effect.
The inductive effect is permanent but feeble, as it involves the shift of strongly held σ-bond electrons, and other stronger factors may overshadow this effect.
en.allexperts.com /e/i/in/inductive_effect.htm   (529 words)

  
  Mesomeric effect: Encyclopedia topic   (Site not responding. Last check: 2007-10-26)
The Mesomeric effect is the effect of the overlap of a p-orbital (orbital: in atomic physics, the electron configuration is the arrangement of electrons in...
The effect is symbolized by M. The mesomeric effect of delocalised electrons occurs in unsaturated organic compounds, where the double bond is separated by a single bond.
Additionally, the effect of delocalising the electrons and therefore the charge, will reduce the probability of the anion (anion: A negatively charged ion) being reprotonated as it is now a "soft nucleophile" (disperse charge) compared to the "hard electrophile" of the proton (small localised charge).
www.absoluteastronomy.com /reference/mesomeric_effect   (232 words)

  
 Wikipedia: Phenol
Phenol has antiseptic properties, and was used by Sir Joseph Lister in his pioneering technique of antiseptic surgery, though the skin irritation caused by continual exposure to phenol eventually lead to the substitution of aseptic (germ-free) techniques in surgery.
Exposure of the skin to concentrated phenol solutions causes chemical burns; in laboratories where it is used, it is usually recommended that polyethylene glycol solution is kept available for washing off splashes.
Notwithstanding the effects of concentrated solutions, it is also used in cosmetic surgery as an exfoliant, to remove layers of dead skin.
www.factbook.org /wikipedia/en/p/ph/phenol.html   (295 words)

  
 Defintion of polar_effect - Chemistry Dictionary   (Site not responding. Last check: 2007-10-26)
For a reactant molecule RY, the polar effect of the group R comprises all the processes whereby a substituent may modify the electrostatic forces operating at the reaction centre Y, relative to the standard RoY.
Sometimes, however, the term "polar effect" is taken to refer to the influence, other than steric, that non-conjugated substituents exert on reaction rates, i.e.
effects connected with electron delocalization between a substituent and the molecular framework to which it is attached are excluded.
www.bonus.com /contour/Chemicool/http@@/www.chemicool.com/definition/polar_effect.html   (159 words)

  
 Phenol
In effect, phenols are a class of organic compounds of which the phenol discussed in this article is the simplest member.
Washing with large amounts of plain water (most labs have a safety shower or eye-wash) and removal of contaminated clothing are required, and immediate ER treatment for large splashes; particularly if the phenol is mixed with Chloroform (a commonly used mixture in molecular biology for DNA purification).
Notwithstanding the effects of concentrated solutions, it is also used in cosmetic surgery as an exfoliant, to remove layers of dead skin.
www.ufaqs.com /wiki/en/ph/Phenol.htm   (433 words)

  
 Mesomeric Effect   (Site not responding. Last check: 2007-10-26)
Mesomeric effect attributed to a substituent in chemical compounds due to overlap of its p- or pi-orbitals with the p- or pi-orbitals of the rest of...
Mesomeric effect Mesomeric effect attributed to a substituent in chemical compounds due to overlap of its p- or pi- orbitals with the p- or...
Encyclopedia - Mesomeric effect Mesomeric effect attributed to a substituent[?] in chemical compounds due to overlap of its p- or pi-orbitals with...
www.varicosity.info /info/Mesomeric-Effect   (247 words)

  
 Help needed with Aryl Carbocation stability and Electrophilic Aromatic Substitution Text - Physics Forums Library
So I need you to tell me why mesomeric effect doesn't occur when an resonance-based electron donating group is meta with respect to a group G? In this case, I think the benzylic group is strongly electron withdrawing (inductively) as it has a positive charge on it.
I do not know what my teacher thinks of the meta directing effect, but all that he has told us is that the stabilizing effect of a +M group due to +M effect is zero when the group is meta with respect to a group G already present.
Let me write what I've found during studying with a student; inductive effect is a matter of electronegativity of the atom attaching the benzene ring, where mesomeric effect is determined as the lone electron pair contribution of this group.
www.physicsforums.com /archive/index.php/t-43227.html   (2452 words)

  
 Phenol - Wikipedia, the free encyclopedia
The word phenol is also used to refer in general to an aromatic compound in which a hydroxyl group (-OH) is bonded directly to a six-membered aromatic ring.
In effect, phenols are a class of organic compounds of which the phenol discussed in this article is the simplest member.
Washing with large amounts of plain water (most labs have a safety shower or eye-wash) and removal of contaminated clothing are required, and immediate ER treatment for large splashes; particularly if the phenol is mixed with chloroform (a commonly used mixture in molecular biology for DNA purification).
en.wikipedia.org /wiki/Phenol   (454 words)

  
 Mesomeric effect - TheBestLinks.com - Electron configuration, Chemical compound, Substituent, Inductional effect, ...   (Site not responding. Last check: 2007-10-26)
Mesomeric effect attributed to a substituent in chemical compounds due to overlap of its p- or pi-orbitals with the p- or pi-orbitals of the rest of the molecular entity.
The effect is symbolized by M. It occurs in unsaturated organic compounds, where the double bond is separated by a single bond.
The effect is responsible for stability, unusual to unsaturated compounds.
www.thebestlinks.com /Mesomeric_effect.html   (131 words)

  
 General Chemistry Online: FAQ: Chemical bonds: What do the terms 'mesomeric effect' and 'inductance effect' mean?
If electron density at a particular point in a molecule is higher or lower than what you'd expect from a single Lewis structure, and various canonical structures can be drawn to show how electron delocalization will explain the discrepancy, the difference in electron density is called a "mesomeric effect".
An inductive effect is the polarization of a chemical bond caused by the polarization of an adjacent bond.
(Field effects are polarization caused by nonadjacent bonds).
antoine.frostburg.edu /chem/senese/101/bonds/faq/print-mesomeric-effect.shtml   (120 words)

  
 [No title]
The effect of hydroxyl radicals, produced by =Fenton's reagent, on cholesterol and its acetate and hydrogen =succinate in aqueous acetic acid solution is summarised in the table.
In =(2) the effect should be greater, in =(3) less, the greater the electron affinity =(q) of the hetero-element or =E group.
The effect in =(C) should be greater, in =(6) less, the greater the electron affinity of the =hetero-element or =-E group.
www.soc.cornell.edu /hayes-lexical-analysis/CornellCorpus2000/UKSCIENC/CHE1950A.ASC   (1172 words)

  
 Glossary - M
Macrocyclic Effect: A complex formed with a closed ring ligand is more stable than its open chain analogue.
Madelung Constant: This is the factor by which the ionic charges must be scaled to allow for the different arrangements of ions in different structures.
Mesomeric Effect: The mesomeric effect occurs through π bonds, and can either add (if there are filled p orbitals - as on O or N) or remove (if there is an empty p orbital) local electron density.
www.everyscience.com /Chemistry/Glossary/M.php   (611 words)

  
 Definition of Mesomeric effect
The effect is symbolized by M. It occurs in unsaturated organic compounds, where the double bond is separated by a single bond.
The effect is responsible for stability, unusual to unsaturated compounds.
It also affects acidity of certain compounds by weakening the inductional effect.
www.wordiq.com /definition/Mesomeric_effect   (145 words)

  
 Halogenation of protected phenols in meta position - Patent 6576782
The process according to claim 1, wherein one or two of the electron-withdrawing functional groups are electron-donating group by mesomeric effect.
The problem is often complicated by the directing effect of some functional groups, in particular when these functional groups have a very marked directing effect, as is the case with phenol functional groups and their derivatives and aniline functional groups and their derivatives.
The most advantageous effects are obtained in the case where said electron-withdrawing functional groups, in any event at least one, preferably both, are halogen atoms.
www.freepatentsonline.com /6576782.html   (3024 words)

  
 ARKAT USA, Inc.
Electronic effects due to the substitution are found not to increase significantly, and often to decrease, the calculated coupling, since they involve mainly p orbitals, while the coupling is mainly transmitted through s orbitals.
It is useful, at this point, to recall some qualitative considerations on the effect of substituents on the energetics of the CH/p dimers [5].
However, we should recall that the FC contribution is transmitted by s-type orbitals, since it requires the probability, and therefore the wave function of the electron, to be non-zero at the nucleus.
www.arkat-usa.org /home.aspx?VIEW=MANUSCRIPT&MSID=380   (1333 words)

  
 International Union of Pure and Applied Chemistry
Relativistic effects - Corrections to exact nonrelativistic energy from the fact that inner shell electrons in heavy atoms move with velocities comparable in order of magnitude to the velocity of light.The most important relativistic effect is spin-orbit coupling.
The Renner effect is a particular case of the Jahn-Teller effect.
Dewar resonance energy, DRE, is the quantity which allows one to account for the effects of cyclic electron delocalization and thus serves as a measure of the aromatic stabilization (see aromaticity) of a cyclic molecular entity.
sunsite.informatik.rwth-aachen.de /iupac/reports/1999/7110minkin/q-r.html   (1193 words)

  
 Reactions and Reactants
If the carbon atom attached to the polarizing atom or group is itself attached to further carbon atoms, the inductive effect is transmitted along the chain, although it tends to be insignificant beyond the second carbon.
The effect is transmitted along a chain in a way similar to the inductive effect.
The mesomeric effect is of paramount importance in conjugated chains of carbon atoms (i.e.
lky.hkcampus.net /~lky-ask/chem/org/reactions/reactions.htm   (732 words)

  
 General Chemistry Online: Glossary: Chemical bonds
The inert pair effect explains why common ions of Pb are Pb and Pb, and not just Pb as we might expect from the octet rule.
The actual ground state doesn't switch rapidly between the separate structures: it is an average.
If electron density at a particular point in a molecule is higher or lower than what you'd expect from a single Lewis structure, and various canonical structures can be drawn to show how electron delocalization will explain the discrepancy, the difference in electron density is called a "resonance effect" or "mesomeric effect".
antoine.frostburg.edu /chem/senese/101/bonds/glossary.shtml   (1189 words)

  
 SYLLABUS TC
Effect of salt concentration and M/L ratio on exhaustion of direct dyes.
Effect of carrier concentration on dye uptake of polyester.
Effect of fibre structure on dyeability and diffusion of dyes.
www.titsbhiwani.org /tcsyllabus.htm   (2823 words)

  
 Indian Journal of Chemistry   (Site not responding. Last check: 2007-10-26)
The effect of counterion and hydrogen ion concentrations on the capacity factor of weak monoprotic organic acids in ion‑pair reversed phase chromatography
In both the compounds, short H-bonding contacts are observed between the oxygen atoms bound to the Cr containing dianion and the H attached to the N atom of the organic dication.
The shifts in the position of CT band of PQ-purinate and the variation of its stability constant with substituents are explained in terms of the number of substituents, the ionization of substituents, the mesomeric effect of substituents and the hyperconjugation of substituents in the purine ring.
www.niscair.res.in /ScienceCommunication/ResearchJournals/rejour/ijca/ijca2k3/ijca_nov03.asp   (3155 words)

  
 Synthesis of fluorocarbon compounds
The present invention relates to the synthesis of hydrocarbon compounds which are fluorinated on a carbon atom of an "alkyl" moiety thereof via exchange between a halogen atom having an atomic number greater than fluorine, employing a fluorine-containing reactant which is at least partially in the form of a complex salt.
Thus, the exchange reactions are essentially successive (in effect, each additional fluorine atom on the halophoric carbon slows the exchange of halogen atoms heavier than fluorine with the latter), thereby making it possible to carry out a selective or complete exchange, by varying the operating conditions and the choice of reactants.
When R.sub.5 is electron-withdrawing, especially via mesomeric effect, it should be appreciated that the exchange is more difficult, especially for the third fluorine atom on the same carbon.
www.devileye.net /catalog/current_interrupter_electrochemical_cells/synthesis_fluorocarbon_compounds.html   (5820 words)

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