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	Functional Groups - Bonding
		The term pi is used because half of this bond extends above the plane of all three sigma bonds and half extends below that plane.
		The pi electrons are farther away from the nuclei and are less strongly held to them than are sigma electrons.
		All the electrons associated with the carbon and hydrogen atoms are involved in bonding, and each has a completely occupied valence shell.
	chemistry2.csudh.edu /rpendarvis/funcgr.html (1334 words)

	Electron configuration (Site not responding. Last check: 2007-10-25)
		Since electrons are fermions they are subject to the Pauli exclusion principle, which states that no two fermions can occupy the same quantum state at once.
		This is the fundamental basis of the configuration of electrons in an atom: once a state is occupied by an electron, the next electron must occupy a different quantum mechanical state.
		The chemical properties of an atom are largely determined by the arrangement of the electrons in its outermost ("valence") shell (although other factors, such as atomic radius, atomic mass, and increased accessibility of additional electronic states also contribute to the chemistry of the elements as atomic size increases).
	www.sciencedaily.com /encyclopedia/electron_configuration (953 words)

	Aromaticity - Wikipedia, the free encyclopedia
		In chemistry, an aromatic molecule is one in which electrons are free to cycle around circular arrangements of atoms, which are alternately singly and doubly bonded to one another.
		A better representation is that of the circular pi bond, in which the electron density is evenly distributed through a pi bond above and below the ring.
		The circulating pi electrons in an aromatic molecule generate significant local magnetic fields that can be detected by NMR techniques.
	en.wikipedia.org /wiki/Aromaticity (609 words)

	Organic electronics - Wikipedia, the free encyclopedia
		Organic electronics, or plastic electronics, is a branch of electronics that deals with conductive polymers, or plastics.
		It is called ' organic ' electronics because the molecules in the polymer are carbon -based, like the molecules of living things.
		This is as opposed to traditional electronics which relies on inorganic conductors such as copper or silicon.
	en.wikipedia.org /wiki/Organic_electronics (336 words)

	Aromatic [Definition] (Site not responding. Last check: 2007-10-25)
		A better representation is that of the circular pi bond, in which the electron density is evenly distributed through a pi bond In chemistry, Pi bonds are those bonds between two atoms in a molecule that do not exhibit orbital hybridization.
		Pi bonds are weaker than sigma bonds because their orbitals go further from the positive charge of the nucleus, which requires more energy.
		The circulating pi electrons in an aromatic molecule generate significant local magnetic fields that can be detected by NMR Nuclear magnetic resonance (NMR) is a physical phenomenon involving the interaction of atomic nuclei placed in an external magnetic field with an applied electromagnetic field oscillating at a particular frequency.
	www.wikimirror.com /Aromatic (2615 words)

	MSN Encarta - Carbon
		As with all atoms, the electrons in a carbon atom reside in layers, or shells, around the nucleus.
		Electrons in pi bonds are much more reactive than are electrons in sigma bonds.
		That is, pi electrons more easily split away from the bond and create bonds with other atoms, adding those atoms to the molecule.
	encarta.msn.com /encyclopedia_761577017/Carbon.html (1053 words)

	PI Molecular Orbitals
		The two atoms are bonded; the orbital containing the electrons is a bonding MO. If additional electrons had to be accomodated, they would have to go into the higher energy orbital, which has a node between the nuclei.
		The orbital contining the electrons is the highest energy one that is occupied, the HOMO - h ighest o ccupied m olecular o rbital.
		All electrons thus occupy orbitals lower in energy than individual p orbitals, and thus the molecule is stabilized by the interaction of the two double bonds.
	chemistry.umeche.maine.edu /CHY252/Pi-orbs.html (1295 words)

	International Sun-Earth Explorer Observations (Site not responding. Last check: 2007-10-25)
		Protons and electrons in the energy range from 1 eV to 45 keV were measured in 64 contiguous energy bands with an energy resolution (delta E/E) of 0.16.
		A quadrispherical low-energy proton and electron differential energy analyzer (LEPEDEA), employing seven continuous channel electron multipliers in each of its two (one for protons and one for electrons) electrostatic analyzers was flown on both the mother and the daughter spacecraft.
		This detector was sensitive to electrons with E>45 keV, and to protons with E>600 keV.
	www-pi.physics.uiowa.edu /lep (279 words)

	Valence bond theory-Molecular orbital theory-Theories Of Chemical Bonding-Sigma bond-Pi bond-Formation of sigma ...
		An electron in a molecular orbital is polycentric because it is influenced by more than one nuclei.
		A Pi bond is formed by the lateral or side ways or parallel overlapping of P-orbital of the atoms which are already bonded by a sigma bond and their axes are coplanar.
		Pi bond is formed when two atoms already bonded by a sigma bond.
	www.citycollegiate.com /bond_theoryXIa.htm (503 words)

	What is electrophilic addition?
		The pi electrons are not as fully under the control of the carbon nuclei as the electrons in the sigma bond and, because they lie exposed above and below the rest of the molecule, they are relatively open to attack by other things.
		As the process continues, the two electrons in the pi bond move even further towards the X until a covalent bond is made.
		The pi bond was originally made using an electron from each carbon atom, but both of these electrons have now been used to make a bond to the X atom.
	www.chemguide.co.uk /mechanisms/eladd/whatis.html (1262 words)

	RESONANCE THEORY (Site not responding. Last check: 2007-10-25)
		This is because all six of the pi electrons in benzene are delocalized over all six atoms and are not uniquely shared by a given pair of two atoms.
		Note that the electrons that are moved in benzene are the electrons of the pi bond (called pi electrons).
		The electrons may be in pi bonds, as in the case of benzene, or on atoms, as in the case of acetate ion.
	neon.cm.utexas.edu /bauld/teach/notes3.html (1008 words)

	Chapter 20: Benzene and Derivatives: Aromaticity (Site not responding. Last check: 2007-10-25)
		Aromaticity depends upon the number of electrons in the cyclic conjugated system (the electron count), and not upon either the size of the ring or whether it is neutral or negatively or positively charged.
		The electron count is obtained by examining any one canonical structure of the anion, and counting 2 electrons per pi bond and 2 electrons for a carbanion center (the carbanion center has a 2p AO which is doubly occupied).
		Although naphthalene has 10 pi electrons and its aromaticity could be considered to be based upon having the magic number of electrons, it should be noted that the 4n+2 rule does not strictly apply to polycyclic systems.
	www.cm.utexas.edu /bauld/teach/ch610bnotes/ch20.htm (3866 words)

	World of Carbon (Site not responding. Last check: 2007-10-25)
		In this type of bonding the electron density is highest in the space between the atoms.
		The interaction of the loosely held electrons, in the pi bonds, with light is responsible for its fl color.
		Since the valence electrons in diamond are involved in the formation of sigma bonds and no delocalized pi bonds, diamond has very poor electrical conductivity.
	invsee.asu.edu /nmodules/Carbonmod/bonding.html (725 words)

	Bad Astronomy Bulletin Board :: View topic - Black Hole FAQ (Site not responding. Last check: 2007-10-25)
		He suggested that electrons in the atom can only occupy discreet energy levels and the only time energy is transferred is when an electron moves between these energy levels.
		Electrons are prevented from merging with nuclei by the nuclear forces.
		Electron degeneracy pressure (that which supports white dwarf stars) steps in to say hello for a bit, but is soon shown the door....because a process known as neutronization kicks in at about this point.
	www.badastronomy.com /phpBB/viewtopic.php?t=6307&start=125 (3409 words)

	Duplex, Super Duplex, Titanium, 6% Moly, Valves-tubing, pipe, fittings, flanges, round bar & plate: Ocean International ...
		The shared electron pairs are held tightly in sigma bonds between adjacent atoms.
		The fourth electron of each atom becomes part of an extensive pi bond system.
		Graphite conducts electricity, because the electrons in the pi bond system can move around throughout the graphite.
	www.oceanint.com /content/interior.asp?section=elements&body=carbon&ti... (3409 words)

	11th Hour - Organic Chemistry I & II
		Usually one just counts up the eight electrons without really thinking about how the four valence orbitals (an s and three p orbitals, or some combinationof hybrids and p orbitals) hold 2 electrons each so when the valence shell is filled that means 8 electrons.
		Note that the 6 pi electrons reside in 3 bonding pi MOs of benzene.
		The reason groups with a nonbonded electron pair on the atom attached to the ring are normally o/p directing activators is because that pair of electrons is resonance delocalized into the ring.
	www.blackwellpublishing.com /11thhour/book6/oc1ch8.html (1611 words)

	Explaining electrophilic addition involving bromine and unsymmetrical alkenes
		As the bromine molecule approaches the pi bond, the electrons in that bond repel the electrons in the bromine-bromine bond down towards the bottom bromine.
		The electrons from the pi bond move down towards the slightly positive bromine atom.
		In the second stage of the mechanism, the lone pair of electrons on the bromide ion is strongly attracted to the positive carbon and moves towards it until a bond is formed.
	www.chemguide.co.uk /mechanisms/eladd/unsymbr2tt.html (685 words)

	A Most Unusual Superconductor and How It Works
		What was puzzling was that, in BCS theory, the coupling to the lattice required to form an electron pair should be equivalent to the coupling of a single electron emitting and reabsorbing a phonon, giving rise to an enhanced electron mass.
		MgB2, like graphite, has strong sigma bonds in the planes and weak pi bonds between them, but since boron atoms have fewer electrons than carbon atoms, not all the sigma bonds in the boron planes are occupied.
		The two kinds of electron pairs are coupled, and as temperature increases the superconducting gaps for "red" and "blue" pairs rapidly converge, until at about 39 degrees K both vanish.
	www.lbl.gov /Science-Articles/Archive/MSD-superconductor-Cohen-Louie.html (1460 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 (1962 words)

	Werner Kutzelnigg - Publikationsliste
		Simulation of the influence of the core electrons by a pseudopotential.
		Electron correlation and the rotational barrier of ethane.
		Electron correlation at the dawn of the 21
	www.theochem.rub.de /members/kutzelnigg/kutzelnigg_pubs.de.html (2548 words)

	bonding in benzene - sp2 hybridisation and delocalisation
		Notice that the p electron on each carbon atom is overlapping with those on both sides of it.
		Because the electrons are no longer held between just two carbon atoms, but are spread over the whole ring, the electrons are said to be delocalised.
		The delocalisation of the electrons means that there aren't alternating double and single bonds.
	www.chemguide.co.uk /basicorg/bonding/benzene2.html (877 words)

	Name of File
		The two Pi electrons are freely able to move over this three carbon structure which has a tendency to spread the Positive charge over three atoms instead of only two thereby stabilizing the allyl carbocation.
		This allows the unpaired electron that resulted from the homolytic cleavage and the Pi electrons to be delocalized along that three atom allylic system The C-4 carbon is not part of this delocalization because it is an sp3 carbon and as such has no "p" orbital to contribute to the pipeline.
		The electron density of the unpaired electron of the allylic free radical is distributed over the C-1 and C-3 carbon but not evenly.
	members.aol.com /profchm/conj.html (2380 words)

	Abstracts Theoretical Chemistry
		While usually the analysis of electron correlation is in terms of the global features of the electronic density, the present analysis is made in terms of the near degeneracy of low-lying excited configurations; this allows a clear physical interpretation of the effects considered.
		We study the dynamics of the electronic and nuclear degrees of freedom for molecules in strong laser fields using an ansatz for the wavefunction that explicitly incorporates the electron-nuclear correlation.
		The unpaired electron on O is low-spincoupled to the V d electrons and spin density is predicted to be localized on vanadium.
	theochem.chem.rug.nl /publications/Abstracts.html (14672 words)

	PSC 3320 - Principles of Drug Action
		There are still two pairs of pi electrons, but the geometry of this type of oxygen is obviously quite different.
		Thus, the 4 pi electrons plus the two lone pair electrons add up to 6 pi electrons, which is a Huckel number.
		Because of the electron withdrawing character of the sulfone moiety in a sulfonamide, combined with the electron withdrawing character of the phenyl ring, the bond between the nitrogen and the hydrogens is extremely weak.
	wiz2.pharm.wayne.edu /module/acidbase.html (6417 words)

	C 2131 Electrophilic Aromatic Substitution Reactions
		An important difference between these two reaction types is that in the former the pi bond is lost and replaced by two sigma bonds, and in the latter there is no net loss of pi electrons.
		A lone pair on bromine attacks the electron deficient iron atom togive a complex where the iron atom is negatively charged and the closest Br is positively charged.
		the electrons of the carbon-chloride bond of the acyl chloride attack the electron deficient aluminum atom of the catalyst to give a molecular complex where the Cl is positively charged and the Al is negatively charged.
	www.mta.ca /~acockshu/c2131aromsubst.html (1402 words)

	Nucleophilic Substitution & Elimination
		Here there are no valence electrons other than the ones holding the hydrogens to the carbon, so there is a very poor supply of electrons to assist with lowering the energy of the carbocation.
		There are more electrons available on the carbon atoms attached to a tertiarly carbocation center than there are on the hydrogens attached to a methyl carbocation center.
		Recall that pi electrons are less tightly bound than sigma electrons, so they are easier to move towards the electron deficiency.
	chemistry2.csudh.edu /rpendarvis/SN1Elim.html (2034 words)

	Chapter 9: Molecular Geometry and Bonding Theories
		single bonds are sigma bonds, double bond consists of one sigma bond and one pi bond, triple bond consists of one sigma bond and two pi bonds
		localized bonding — sigma and pi electrons are associated totally with the two atoms that form the bond
		1) in every bond at least one pair of electrons is localized in space between atoms in a sigma bond.
	www.geocities.com /wh0ami5/htmlnotes/Chapter9.htm (1154 words)

	Additions to Alkenes
		These steps -- first an electrophile attacks the pi bond to form a carbocation, second a nucleophile attacks the carbocation -- are the key steps in the most important reactions of alkenes, electrophilic addition reactions.
		We have explained this by saying that the the electrons in a methyl group are better at partially relieving the carbocation's electron deficiency than the relative lack of electrons around a hydrogen.
		One bond is made using the electrons from the pi bond, and the other is made using an unshared electron pair from the bromine.
	chemistry2.csudh.edu /rpendarvis/AlkeneAddn.html (1583 words)

	Chemistry 101A, Atomic and Molecular Oribtals Page
		In this orbital most of the electron "density" is in the two outer lobes of the orbital, but there is some electron density in the two small inner lobes.
		The 2p-sigma orbital is a bonding orbital which can be approximated by two 2p orbitals with their electron density lobes pointing toward each other.
		Since there are only six pi electrons in the benzene molecule only the lowest three pi orbitals will be occupied.
	www.chem.arizona.edu /~salzmanr/orbitals.html (1640 words)

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