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Topic: Delocalized electron

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	Delocalized electron - Wikipedia, the free encyclopedia
		In chemistry, delocalized electrons are electrons in a molecule that do not belong to a single atom or a covalent bond.
		Delocalized electrons are part of a pi electron system that extends over several adjacent atoms.
		Delocalized electrons can be found in conjugated systems of double bonds and in aromatic systems.
	en.wikipedia.org /wiki/Delocalized_electron (269 words)

	Delocalized electron -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-10)
		Delocalized electrons are part of a (additional info and facts about pi electron) pi electron system that extends over several adjacent atoms.
		Delocalized electrons can be found in (additional info and facts about Conjugated system) Conjugated systems of (A covalent bond in which two pairs of electrons are shared between two atoms) double bonds and in (additional info and facts about aromatic) aromatic systems.
		In the (additional info and facts about simple aromatic ring) simple aromatic ring (A colorless liquid hydrocarbon; highly inflammable; carcinogenic; the simplest of the aromatic compounds) benzene the delocalization of six pi electrons electrons over the whole ring is often indicated by the circle:
	www.absoluteastronomy.com /encyclopedia/d/de/delocalized_electron.htm (229 words)

	Electronic Properties (Site not responding. Last check: 2007-10-10)
		Electrons in solids are in localized or delocalized states, levels, or orbitals.
		This is the electron affinity in the case of a non-metal.
		Electrons are bound to atoms and corrections are added for overlap of the electron density produced by different atoms.
	www.virginia.edu /ep/SurfaceScience/electron.html (2062 words)

	Why are plants green? Why are flamingos pink? (organic compounds)
		These electrons, no longer localized in a double bond between two adjacent atoms, are now free to range over the whole molecule and hence are "delocalized." This electron delocalization stabilizes the molecule.
		Delocalized electrons, held in molecular orbitals, can absorb visible light, thereby becoming the source of color.
		An alternating sequence of single and double bonds is therefore the necessary structural requirement for color in organic molecules, because it produces electrons delocalized in molecular orbitals.
	webexhibits.org /causesofcolor/7.html (1983 words)

	NANOTECHNOLOGY: ON CORRELATED ELECTRONS
		Electron flow from one lead to the other through the artificial impurity serves as a powerful probe of local electronic states.
		Such strongly interacting or "correlated" electrons cannot be described as embedded in a static mean field generated by the other electrons.(1) The influence of an electron on the others is simply too pronounced for each to be treated independently.
		However, when the number of free electrons in a solid becomes comparable to the number of the constituent atoms and the mutual electron-electron interaction becomes strong, electrons may lose their mobility.
	scienceweek.com /2005/sw050610-5.htm (1765 words)

	ROCO Resonance: Delocalized
		The easiest way to spot delocalized electrons is to compare electron locations in two resonance forms.
		A delocalized bond is a bond that appears in some resonance forms, but not others.
		A delocalized charge is a formal charge that appears on one atom in some resonance forms and on other atoms in other forms.
	academic.reed.edu /chemistry/roco/Resonance/delocalized.html (247 words)

	Chem - Option H - Further organic chemistry
		This causes the electrons from the H-Cl bond to be moved onto the Cl atom.
		If an electron withdrawing group (such as a halogen) is connected to the delta +ve carbon being attacked, then the delta +ve charge will be increased, resulting in a greater rate of nucleophillic substitution.
		These are very weak bases due to the electron withdrawing effect of the C=O group, which reduces the negative charge on the N atom, making it less able to attract protons, and less stable once it has one.
	homepage.mac.com /stray/ib/chem/Options/organic.html (2278 words)

	Slides32 (Site not responding. Last check: 2007-10-10)
		The nine pairs of delocalized electrons fill the orbitals within the model as indicated.
		The next two electrons go into a localized bonding pi orbital made from 2p atomic orbitals on neighboring C and N. Four more electrons to dump in somewhere now.
		It takes the last two electrons in a non-bonding geometry that is half on a 2p on the S and half on the 2p on the N where the negative charge is thus shared at the two ends.
	www.andrew.cmu.edu /course/09-105/S98Slides32new.html (375 words)

	Water Buckyballs
		This site is devoted to the electronic structure and low-frequency vibrational modes of water "buckyballs", as well as to the implications of adding electrons to the clusters on their chemical, catalytic, and astrophysical properties.
		If cosmic electrons are traveling close to the speed of light, their interaction with the above-described low-frequency cluster vibronic modes could result in the conversion of the associated water-cluster far-infrared radiation to x-ray or gamma radiation via the inverse Compton effect (ICE).
		This "many-body" electronic effect, JT-coupled with the calculated and measured low-frequency O - O - O vibrations, may explain the unique and still poorly understood properties of liquid water, such as its large heat capacity and anomalous freezing properties.
	www.watercluster.com (2602 words)

	Research
		When the electronic cloud of a molecule is excited (after the absorption of one photon), the ?-electron density is changed, which means that the geometry of the molecule, in particular the distances between the carbon atoms, is slightly changed.
		Therefore, absorption leads to an electronic transition accompanied by a series of vibronic bands where 0, 1, 2, etc. vibration quanta are created along with the electronic excitation.
		The situation is even worse when the molecule is excited, because then the electronic cloud has been given extra energy, which can be used to cross photochemical barriers, or gives access to more new states for the excited electron.
	www.geocities.com /sureshuoh/Research.html (1783 words)

	Glossary of Terms for Computational Chemistry
		Representation of the electron cloud surrounding an atom.
		Electrons which do not reside along a single bond, but move from bond to bond, as in an aromatic carbon bond.
		A measure of the "thickness" of the electron cloud in a given place, eg, the probability of the electron's presence.
	www.shodor.org /chemviz/glossary.html (1468 words)

	Chemical bond Article, Chemicalbond Information (Site not responding. Last check: 2007-10-10)
		The types of bonding aredistinguished by the extent to which electron density is localized or delocalized among the atoms of the substance.
		In the case of ionic bonding, electrons are mainly associated with individual atoms, and an overall electric charge isassigned to discrete constituent atoms throughout the substance.
		By contrast, in covalent bonding the electron density distributions within bonds are not assigned to individual atoms, but areinstead delocalized across the molecule in structures which are described by the most common contemporary theory as molecular orbitals.
	www.anoca.org /atoms/ionic/chemical_bond.html (357 words)

	Journal of Electronic Materials: Observations of deep levels in 4H-SiC using optoelectronic modulation spectroscopy
		An electron trap at 1.20 eV gave the most prominent response with a distinctive signature indicating that these traps were spatially delocalized with an extent of at least 1.35 run, possibly associated with an extended defect structure.
		The effect of the reduced electron trap population in the undepleted channel would be to increase the device current so that in the OEMS experiment it is a positive peak in the current modulation that is observed; the current increases when the photon energy makes a positive excursion.
		The effect of a reduction in the number of trapped electrons in the two depletion regions is to decrease the depletion widths, again producing an increase in channel current.
	www.findarticles.com /p/articles/mi_qa3776/is_200110/ai_n8990858 (1360 words)

	PPT Slide (Site not responding. Last check: 2007-10-10)
		The bond order in O 3 is 3 electron pairs /2 atom-to-atom linkages, or 1 1/2.
		Each bond consists of a single bond (localized electron pair) and a partial bond (contribution from delocalized electron pair).
		Electron delocalization stabilizes the molecule by spreading out the electron density and reducing electron - electron repulsions.
	www.uh.edu /~chem1p/c10/tsld011.htm (71 words)

	Rearrangement
		Since this is a two-electron process (the 2 electrons in the relocated sigma bond), the rearrangement is predicted to be suprafacial.
		The source of this assistance was proposed to be the electron pair of the C1 : C6 sigma bond, which is ideally oriented anti to the sulfonate leaving group.
		An electron deficient nitrogen atom does not have to be a cation, as the nitrene example on the right (green box) demonstrates.
	www.cem.msu.edu /~reusch/VirtualText/rearrang.htm (7059 words)

	MOD2635
		wave-particle duality for a free electron moving in a given space, say the macroscopic dimensions of a ring of radius r, requires that the wave associated with the particle fit an integer number (m) of times in the space of motion, the circle.
		The phase space where the electrons are described consists of the linear momentum, the position and spin coordinates.
		It may be explained by the interaction of electrons with lattice waves that couple both the spins and the momenta associated with the conduction electrons.
	www.sjsu.edu /faculty/Acrivos/mod2635.html (1950 words)

	Natia Frank - University of Washington Department of Chemistry (Site not responding. Last check: 2007-10-10)
		Through careful design and investigation of the structural and electronic factors governing the relationships between magnetic exchange interactions and conducting or excited state phenomena, development of a fundamental understanding of the physical principles will allow prediction of such relationships in both materials and biological contexts.
		(I) Organic Spintronics: The implications of magnetic exchange interactions in electron delocalized systems (adiabatic regime) in which the effect of conductivity, electron mobility, and orbital mixing on magnetic exchange, and the effect of exchange interactions on conductivity and spin polarized transport is explored.
		In electron localized systems, or the nonadiabatic regime, through-bond exchange interactions and electron transfer processes are dominated by superexchange processes, in which the electronic parameters that govern exchange interactions and electron transport are fairly well understood.
	depts.washington.edu /chemfac/frank.html (763 words)

	A Different Story of -Delocalization-The Distortivity of -Electrons and Its Chemical Manifestations (Site not responding. Last check: 2007-10-10)
		The concept of electronic delocalization has germinated in the pre-electron period to Kekulé's 'structural theory' and its application to benzene as a prototype of a family of compounds so-called "aromatics".
		The exalted diamagnetism was interpreted to result from the ring currents carried by the delocalized electrons which circulate under the influence of the external magnetic field in orbits with radii that are determined by the path of delocalization.
		This means that delocalization of the 4N + 2 electrons is supported by overlap of the atomic orbitals, while for 4N electrons the resonance energy is due to the lowering of the Coulomb correlation energy.
	pubs.acs.org /cgi-bin/jcen?chreay/101/i05/html/cr990363l.html (12362 words)

	The Condo Effect in a Single-Electron Transistor (Site not responding. Last check: 2007-10-10)
		The solution of the Kondo problem, the behavior of an impurity atom with an unpaired electron in a metal, is one of the triumphs of modern physics.
		After decades of research we now know that at low temperatures a spin-singlet state is formed between the unpaired localized electron and delocalized electrons at the Fermi energy.
		In the SET the droplet of electrons is analogous to the impurity and the leads play the role of the metal.
	www.phy.duke.edu /~rps/coll99/kastner.html (153 words)

	Aromatic Hydrocarbons
		Since each carbon has four valence electrons, three of them are in the three sp2 hybrid orbitals with the fourth electron in the unhybridized "p" orbital and delocalized.
		Resonance Electronic Effect- This effect relies upon electrons in "p" orbitals being in conjugation with the Pi electrons of the ring.
		To understand this you have to think of a ring that is deactivated,but a ring which the relative electron density is greater at the ortho and para positions due to the resonance effect of the lone pairs.
	members.aol.com /logan20/aromatic.html (2608 words)

	David A. B. Miller - Abstracts
		The most striking effect is that the minimum splitting of the excitons associated with each of the split electron levels does not occur at the same field as for the minimum splitting of the bare-electron levels.
		One unexpected but readily observable consequence is that when the same electron-sublevel splitting is measured using two different pairs of intrawell and interwell exciton transitions, the field for minimum exciton splitting can differ by up to approximately 10% from one pair of transitions to the other.
		The authors have constructed a variational model of the coupled excitons that explains these effects in terms of Coulomb mixing of the delocalized electron states.
	www-ee.stanford.edu /~dabm/147.html (286 words)

	ScienceWeek
		In general, an "orbital" is a space region in which an electron may be found in an atom or molecule, the space region essentially a probability distribution for the electron described by the equations of quantum mechanics.
		A hole effectively behaves as an electron with a positive charge, and electrons and holes are known as the "charge carriers" in a semiconductor.
		In general, "electroluminescence" is the emission of light by a substance as the result of an applied electric field, and in general, a "light-emitting diode" (denoted as LED) is a semiconductor device that converts electrical energy into light or infrared radiation, a radiation wavelength span from 550 nanometers (green light) to 1300 nanometers (infrared radiation).
	scienceweek.com /2000/sw001208.htm (4999 words)

	What is a delocalized electron?
		Usually electrons in materials are bound to one atom, and atoms are held together by the interactions of the charges on different atoms.
		In metals, electrons are delocalised over the whole crystal structure, and carry currents - the outer electrons of the metal atoms are shared in an electron sea, and are not confined to particular atoms.
		To really visualize this you have to think of an electron as a probability cloud, and just see that cloud spread over more than one atom; then it's not such a leap to see a delocalised cloud spread all through a metal.
	www.physlink.com /education/askexperts/ae241.cfm (179 words)

	H.K.Joshi's Homepage
		AM1 is an electronic structure calculation method it takes into account the electronic factors and realizes that the nitrogen lone pair can be delocalized in the ring if the angle of the N-H bond with respect to the N-C2-C2' plane is close to zero.
		Gaussian 6-31G (the one I choose as basis set) calculations show first bond (c2 -c3 and c2'-c3') to be closer to a double bond and c3-c3' between a single and double bond.
		If both the electronic potential and the frontier orbitals control the protonation then protonation will be most favored at c3 or c3' positions.
	www.chem.arizona.edu /~joshih/c518.dir/assgn12.html (276 words)

	Metal-Ceramic Interfaces (Site not responding. Last check: 2007-10-10)
		The O atoms are identified by the large red annular regions, as alumina is a very ionic material, with most of the charge pulled towards the anions.
		In contrast, the ELF in the Al shows delocalized, free-electron-like behavior.
		It is capable of illustrating covalent, ionic, and metallic bonding in a concise graphical manner, and can give the location of bonded electron pairs, dangling bonds, and lone pairs.
	ceaspub.eas.asu.edu /cms/research/interface_elf.htm (316 words)

	Electron- and Photon-Induced Localized Atomic Reaction of Halobenzenes with Si
		Electron- and photon-induced reaction of chlorobenzene (ClPh) [ref. 1], 1,2-dichlorobenzene (1,2-diClPh) and 1,4-dichlorobenzene (1,4-diClPh) [ref. 2] adsorbed on silicon (Si(111)7x7) has been shown by Scanning Tunneling Microscopy (STM) to result in 'Localized Atomic Reaction' (LAR), imprinting Cl as chemically-bound Cl-Si on the surface.
		For the ClPh adsorbate, voltage pulses of -4V from the STM tip served to demonstrate LAR restricted to the region of electron impact.
		Delocalized electron impact, customarily used in this laboratory, imprinted the pattern of 'parent' ClPh(ad) on the surface as 'daughter' Cl-Si.
	www.foresight.org /Conferences/MNT8/Abstracts/Polanyi (270 words)

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