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Topic: Hypervalency

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	Modern Approaches to Inorganic Bonding (Site not responding. Last check: 2007-11-03)
		3.2 Hypervalency: (i) PF (a) Symmetry of fragment orbitals
		P does not 'exceed its octet' and the term 'hypervalent' is misleading.
		The lack of first-row analogues such as NF and OF is often ascribed to the lack of d-orbitals in the n=2 shell.
	www.hull.ac.uk /php/chsajb/symmetry/ho_3/ho_3.html (1525 words)

	International Union of Pure and Applied Chemistry
		Hypervalency - The ability of an atom in a molecular entity to expand its valence shell beyond the limits of the Lewis octet rule.
		Hypervalent compounds are common for the second and subsequent row elements in groups 15-18 of the periodic table.
		A description of the hypervalent bonding implies a transfer of the electrons from the central (hypervalent) atom to the nonbonding molecular orbitals which it forms with (usually more electronegative) ligands.
	www.iupac.org /reports/1999/7110minkin/h.html (2220 words)

	Lewis Structures' Tutorial: Part 4- Hypervalency
		There is still a lot of disagreement among chemistry educators about this concept of "hypervalency" (more than eight electrons about the central atom) and when to use it.
		Just like you couldn't conjure up electrons for the central atom when you were short (and thus the concept of multiple bonds between the central and surrounding atom(s)), you can't simply look the other way and sweep the extra electrons under the rug in the hopes that nobody was watching.
		This is the section on hypervalency and xenon is in period 5.
	chemistry.alanearhart.org /Tutorials/Lewis/lewis-part4.html (593 words)

	Three-center four-electron bond - Wikipedia, the free encyclopedia
		The 3-center-4-electron bond is a model used to explain bonding in hypervalent molecules such as phosphorus pentafluoride, sulfur hexafluoride, and the xenon fluorides.
		This localization of charge is accommodated by the fact that the terminal ligands are highly electronegative in hypervalent molecules.
		Older models for explaining hypervalency invoked d orbitals; however, quantum chemical calculations suggest that d-orbital participation is negligible due to the large energy difference between the relevant p (filled) and d (empty) orbitals.
	en.wikipedia.org /wiki/Three-center_four-electron_bond (348 words)

	Chemistry of Hypervalent Compounds
		Broad, comparative coverage of hypervalent compounds -a much-needed foundation in a rapidly growing field of chemistry.
		Although hypervalency is already a mature field in chemistry, it has seen a new surge of interest in recent years due to the discovery of compounds useful in organic synthesis, as well as others with significant applications for materials science.
		A systematic approach using the N-X-L designation, where N represents the valence electrons of the central atom X, and L the ligands that bond the compound.
	www.ramex.com /title.asp?id=13254 (463 words)

	CNR-->Istituto ICCOM --> Articoli JCR (Site not responding. Last check: 2007-11-03)
		Discrepancies between an electron count derived from a recent extension of the Zintl-Klemm rules to electronrich systems (52/3 electrons) and the experimental one (5 electrons for the Sn sublattice) and other failures of chemical common sense emerge in the analysis.
		The key for interpretation of a series of puzzling results was found in the comparative analysis of the Sn net with other main group element hypervalent slabs.
		Increasing s,p-mixing as one moves from the right to the left side of the same row of the periodic table is responsible for these effects.
	www.cnr.it /istituti/ArticoliJCR.html?cds=020&id=28695 (379 words)

	Peter Livant (Site not responding. Last check: 2007-11-03)
		Some pedestrian examples are SF4 or SF6, which would be described as 10-S-4 and 12-S-6 respectively (the first number is the number of electrons associated formally with the central element, followed by the symbol for the central element, and finally the number of ligands about the central element).
		Hypervalent iodine reagents are important synthetic tools in organic chemistry.
		Through synthesis of hypervalent systems of theoretical interest we strive to understand the factors at work in hypervalent bonding.
	www.auburn.edu /academic/science_math/chemistry/faculty_staff/livant.htm (323 words)

	Chemical Reactivity
		The use of phosphorous ylides in the Wittig reaction is an example of this reactivity.
		The reaction of triphenylphosphine with halogens further illustrates this hypervalency.
		The allylic rearrangement observed in thionyl chloride is similarly avoided by using triphenylphosphine dichloride, or alternatively, by a two step procedure by way of a sulfonate ester.
	www.cem.msu.edu /~reusch/VirtualText/special2.htm (6168 words)

	3. Using Symmetry to Understand Bonding (Site not responding. Last check: 2007-11-03)
		This part of the course uses the group theory tools you already know and shows how they can be developed and applied for the construction of molecular orbital diagrams and for understanding the octet and eighteen electron rules, hypervalency and ligand-field effects in transition metal chemistry.
		in which the central main group element appears to expand its octet are known as hypervalent.
		Despite the large number of stable compounds which are classified as hypervalent, hypervalency has remained a controversial subject.
	www.hull.ac.uk /php/chsajb/bonding/ho_3.html (2462 words)

	Spectroscopic evidence indicates that for the BF3molecule the BF bond is a bit tighter than that of a typical B-F bond, ...
		There are a number of ideas regarding the nature of
		hypervalency, and most of them revolve around the idea that these bonds have both ionic and covalent character.
		Also, each of the central atoms in these compounds is in the third row resulting in the presence of d electrons which can be used to "house"' the extra electrons.
	www.csupomona.edu /~egoldstein/121/LDS-COVR.HTM (175 words)

	e-Prints Soton - Synthesis and X-ray crystal structures of organotri(2-furyl)phosphonium salts: effects of 2-furyl ...
		Allen, David W., Coles, Simon J., Light, Mark E. and Hursthouse, Michael B. Synthesis and X-ray crystal structures of organotri(2-furyl)phosphonium salts: effects of 2-furyl substituents at phosphorus on intramolecular nitrogen to phosphorus hypervalent coordinative interactions.
		X-ray structural Studies of the phosphoniobenzimidazole salt reveals the existence of a significant hypervalent coordinative interaction between heterocyclic nitrogen and the phosphonium centre, which also appears to be retained in solution, the P-31 NMR spectrum showing a significantly shielded phosphorus atom, delta(31)P = ca.
		The structure of the phosphoniophenylbenzimidazole cation reveals major distortion of bond angles about phosphorus away from the idealised tetrahedral angles expected for a tetraarylphosphonium salt, in the range 102-116degrees.
	eprints.soton.ac.uk /20116 (470 words)

	MRS Website : Framework Stoichiometry and Electrical Conductivity of Si-Ge Based Structure-I Clathrates (Site not responding. Last check: 2007-11-03)
		This is in sharp contrast to the analogous K-Ge, Rb-Ge and Rb- Sn, Cs-Sn systems, where vacancies are formed at one-third of the crystallographic 6c tetrahedral sites.
		This is rationalized in terms of Zintl-Klemm rules to remove the tetrahedral atom of its hypervalency.
		The contrasting behavior is understood in terms of weaker Tt-Tt (Tt Ð tetrelide, Si, Ge, Sn) bonding as one descends the periodic table, and results in poorly metallic conductivities for vacancy-free K7Si46 and Rb6Si46, but semiconducting behavior of K8Ge44.
	www.mrs.org /s_mrs/sec_subscribe.asp?CID=2376&DID=114249&action=detail (252 words)

	Pentavalent (Site not responding. Last check: 2007-11-03)
		This is more an opportunity to think about what such structures mean than a problem with a single well-defined answer.
		We have already encountered many cases where an atom is "hypervalent", that is, where it forms more bonds than one would expect given its normal valency.
		One type of case is where the atom uses an unshared pair of electrons to mix with someone else's low LUMO, e.g.
	www.chem.yale.edu /~chem125/125/NucleophilicSn/pentavalent.htm (1690 words)

	[No title]
		The values are not exactly periodic, but vary due to the crudity of the model and the variety of chemistry described.
		These include particular bond energies (Al-Cl), hypervalency (P, S), minimal basis set, and/or the lack of d orbitals.
		Gaussians must be added very carefully, as they effect the energy in a direct manner and will "drag" the other parameters during procedure is best, followed by careful optimization.
	www.ccl.net /cca/archived-messages/1992/03/02 (1607 words)

	Chemistry of Hypervalent Compounds:0471240192:Editor: Kin-ya Akiba (Hiroshima Univ., Higashi-Hiroshima, ...
		Chemistry of Hypervalent Compounds:0471240192:Editor: Kin-ya Akiba (Hiroshima Univ., Higashi-Hiroshima, Japan):eCampus.com
		Broad, comparative coverage of hypervalent compounds —a much-needed foundation in a rapidly growing field of chemistry.
		Now, this comprehensive book—written by a group of twenty leading experts in the field—provides an authoritative blueprint on the subject.
	www.ecampus.com /bk_detail.asp?isbn=0471240192&referrer=yah04 (250 words)

	Chemistry 8003: Problem Set 2 Answers
		The reason for this is the lack of d orbitals in the AM1 (or PM3 or MNDO for that matter) Hamiltonian.
		Hypervalency requires d orbitals for proper hybridization, so this calculation fails.
		That is also why the P-O double-bond is so polarized.
	pollux.chem.umn.edu /8021/old/Problem_Set_2_1998_answers.html (731 words)

	Tutorial: Lewis Structures for Covalent Compounds
		When we can use multiple Lewis structures to describe a molecule, we use resonance structures.
		When we need to exceed the octet rule for the central atom, we use the idea of hypervalency.
		And, because you can never have enough practice, here's a chance to practice everything you've learned.
	chemistry.alanearhart.org /Tutorials/Lewis/index.html (283 words)

	361ch2outline2
		Third row and heavier elements can have ______________________.
		Hypervalency is due to the size of atoms and the availability of d orbitals.
		Transition metal complexes do not obey the octet rule, but may _______________________.
	home.messiah.edu /~jmelton/361ch3outline2.htm (198 words)

	Delocalisation in chlorate(VI)
		Anyone who tells you that d-orbitals are involved needs to be beat down, this is a common lie people tell students and it adds nothing to the understanding of the phonomena of hypervalency.
		I think he only means that the charge is not localized on one oxygen but spread accross the entire molecule.
		Also, VSEPR has no way to make sence of Hypervalency only MO theory can handle it properly.
	www.chemicalforums.com /index.php?topic=1920.msg8348 (794 words)

	Title page for ETD etd-0410103-145753
		This is primarily due to the ability of silanes to bond to more ligands than the traditional four to become hypervalent (i.e.
		This hypervalency causes the silicon center to become more Lewis Acidic and causes the formation of carbon nucleophiles from organosilane ligands.
		These nucleophiles have been used to perform many cross-coupling reactions with organohalide reagents.
	etd.lsu.edu /docs/available/etd-0410103-145753 (346 words)

	FAQ and Feedback
		The hang probably results from a case where apparent hypervalency was detected and the program attempted to restart NRT with the NRTFDM option using the full (rather than valence-only) density matrix, but without sufficient memory to accomodate necessary reference structures.
		(Look for the "apparent hypervalency" message near the bottom of the.LOG file to see if this type of hang is likely.) The solution is to provide LOTS of memory for possible hypervalent cases, and/or to include the NRTFDM keyword so that the full density matrix is used from the outset.
		In this case, inadequate memory will lead to an early abort, rather than an infinite hang.
	www.chem.wisc.edu /~nbo5/faq.htm (1173 words)

	UC Davis General Catalog: CHE courses
		Synthesis, physical properties, reactions and bonding of main group compounds.
		Discussions of concepts of electron deficiency, hypervalency, and non-classical bonding.
		Chemistry of the main group elements will be treated systematically.
	registrar.ucdavis.edu /UCDWebCatalog/programs/CHE/CHEcourses.html (2887 words)

	Joseph's Page (Site not responding. Last check: 2007-11-03)
		Here's an ad for me. Considering my opinion of advertising, I shouldn't be messing around with this at all, but here goes...
		Thesis: ``Molecular Orbital Studies of Non-conventional Bonding: Hydrogen Bonding, Hypervalency, and Strained Rings.''
		OK, so I got a Ph.D. in Quantum Chemistry, so sue me! Anyway, here's more about who I am.
	zopyros.ccqc.uga.edu /~joseph (117 words)

	Amazon.com: "strong resonance delocalization": Key Phrase page (Site not responding. Last check: 2007-11-03)
		See all pages with references to strong resonance delocalization.
		neither hypervalency nor strong resonance delocalization is implied by Lewis's original electron-dot picture, which rests on a distinctly ionic (not "elec- troneutral") picture of the bonding.
		Key Phrases in this book: New York, Academic Press, Cornell University Press, Valence Total, John Wiley, Oxford University Press, natural atomic charges, resonance weightings, strong resonance delocalization, strong resonance mixing, natural resonance theory, canted geometry (See more)
	www.amazon.com /phrase/strong-resonance-delocalization (312 words)

	Möbius Aromatic Forms of 8-pi Electron heteropines.
		Solvation has little effect on the relative energies (Table); neither 7d nor 8d is significantly stabilised with respect to the lowest energy species of C
		symmetry, again confirming the higher hypervalency of the phosphorus centre.
		In contrast, the Möbius form 7c shows extension of the N-F bond to 2.03Å but the solvation free energy only decreases about 5 kcal mol
	www.ch.ic.ac.uk /rzepa/mobius-heteropins (2682 words)

	Akiba, Kin-YA; Akiba, Kin'ya; Akiba, Kin-YA: Chemistry of Hypervalent Compounds (Site not responding. Last check: 2007-11-03)
		Akiba, Kin-YA; Akiba, Kin'ya; Akiba, Kin-YA: Chemistry of Hypervalent Compounds
		* An overview of general aspects of structure and reactivity common among hypervalent compounds
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	www.forbesbookclub.com /BookPage.asp?prod_cd=I36C0 (238 words)

	Joseph's Curriculum Vitae (Site not responding. Last check: 2007-11-03)
		Dissertation: Molecular Orbital Studies of Non-conventional Bonding: Hydrogen Bonding, Hypervalency, and Strained Rings.
		Presently working on a research project concerning the difluoro-dioxirene system.
		Last modified: Wed Jan 31 15:35:33 EST 1996
	zopyros.ccqc.uga.edu /~joseph/Docs/cv/cv.html (358 words)

	FERev (Site not responding. Last check: 2007-11-03)
		Besides defining covalent, ionic, and metallic bonding, you will find an introduction to
		with many subtopics: multiple bonding, resonance, hypervalency, electron deficient atoms, and atom formal charge It is also in this chapter that you learned
		I have prepared a one page description of Lewis structures you can link to here or above.
	chemistry.che.georgiasouthern.edu /jlobue/FERev.html (1155 words)

	CERAPIE
		Peter G. University of Hull, Department of Chemistry
		ABSTRACT: A modification to Lewis's theory of valency is proposed to make it more consistent with the results of quantum-mechanical calculations on molecules containing polar covalent bonds (e.g., ClF) and hypervalent atoms (e.g., SF A distinction is drawn between the valence shell of an atom (VS) and the Lewis shell (LS).
		KEY WORDS: Lewis theory; polar covalent bond; hypervalency; valence shell; Lewis shell
	www.uoi.gr /cerp/2001_May/04.html (90 words)

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