
	Where results make sense

Topic: Antiaromatic

	Research-Description
		One of the primary concepts of organic chemistry is that molecules that are aromatic are particularly stable.
		The calculations confirm the antiaromaticity of 1 and also suggest that one consequence of having a positively charged substituent (R+) on the fluorenyl cation is to force electron delocalization throughout the fluorenyl ring system, forcing the entire ring system to be antiaromatic.
		The antiaromaticity of the fluorenyl ring may be affected by its cationic substituent in at least two ways.
	www.trinity.edu /nmills/text/Research-Description.htm (919 words)

	Antiaromatic - Wikipedia, the free encyclopedia
		Antiaromatic (or pseudoaromatic) molecules are cyclic systems containing alternating single and double bonds, where the pi electron energy of antiaromatic compounds is higher than that of its open-chain counterpart.
		Therefore antiaromatic compounds are unstable and highly reactive; often antiaromatic compounds distort themselves out of planarity to resolve this instability.
		Antiaromatic compounds usually fail the Hückel's rule of aromaticity.
	en.wikipedia.org /wiki/Antiaromatic (164 words)

	Reference.com/Encyclopedia/Antiaromatic
		Antiaromatic (or pseudoaromatic) molecules are cyclic systems containing alternating single and double bonds, without having properties common to aromatic compounds.
		Antiaromatic compounds fail the Hückel rule of aromaticity.
		The pi electron energy of antiaromatic compounds is higher than that of its open-chain counterpart.
	www.reference.com /browse/wiki/Antiaromatic (98 words)

	IJQCfinal.html
		It is shown that the antiaromatic character of certain conjugated cyclic hydrocarbons is due to the presence of an even number of distinct electron pairs in the system (such as, but not necessarily, p electrons).
		It is concluded that the properties of antiaromatic molecules are essentially due to the presence of an odd number of different bond types that alternate around the ring, and to the even parity of the system.
		The distortive nature of antiaromatic molecules is found to be a fundamental property of even parity systems, due to the fact that the ground state is formed from the out-of-phase combination of two Kekulé structures.
	chem.ch.huji.ac.il /employee/haas/paper1/ijq.htm (6017 words)

	mills.html
		Calculations on indenyl systems suggests that the indenyl cation is markedly more antiaromatic than the fluorenyl cation.6 The use of NICS suggests that again the 5-membered ring is substantially more antiaromatic than the 6-membered ring.
		We propose to synthesize a series of dications of indenylidenes and examine their antiaromaticity, using the paratropic shifts of protons on both 5- and 6-membered rings.
		It is presumed that the greater antiaromaticity of the 5-membered ring will make its protons more sensitive probes of the paratropic shifts.
	www.trincoll.edu /academics/departments/chem/toms/REUsite/facproj/mills/mill.html (615 words)

	Chem 266H (Site not responding. Last check: 2007-10-15)
		Be able to classify compounds as aromatic, antiaromatic, or non-aromatic by (1) determining whether there is a fully conjugated cycle of p-orbitals, and (2) counting the electrons in that cycle.
		Be able to use thermochemical data, like enthalpies of hydrogenation and group increments, to quantify aromatic stabilization or antiaromatic destabilization relative to a hypothetical non-aromatic reference structure.
		Recognize that antiaromatic compounds, like cyclobutadiene, are strongly destabilized and will distort in any way possible to disrupt or minimize the unfavorable cyclic conjugation.
	people.umass.edu /gjsnyder/Ch16H.html (298 words)

	Do All-Metal Antiaromatic Clusters Exist? (Site not responding. Last check: 2007-10-15)
		antiaromaticity is overcome by the diamagnetic contributions of all the
		) were antiaromatic and destabilized, as claimed, it would adopt a different structure, since the reorganization barriers of such clusters are very low and many alternative geometries are possible.
		Sn MOs precludes mixing of the external lone pair orbitals of the vertex atoms with the tangential surface skeletal orbitals.
	pubs.acs.org /cgi-bin/jcen?jacsat/125/i46/html/ja0361392.html (1157 words)

	C&EN: SCIENCE & TECHNOLOGY - DECIPHERING METAL ANTIAROMATICITY
		For antiaromatic compounds, the shift in ring current is in the opposite direction, referred to as a paramagnetic shift.
		The question of aromaticity and antiaromaticity is thus complicated for these species by cancellation of the currents, Fowler notes.
		Another contributor to the discussion is senior research scientist Dage Sundholm of the department of chemistry at the University of Helsinki, in Finland.
	pubs.acs.org /cen/science/8150/8150sci1.html (3097 words)

	The Hindu : Unstable molecule discovered
		The cyclopentadienyl cation is a common textbook example of an antiaromatic molecule, a molecule so electronically unstable and, therefore, extremely reactive that it should not exist for any length of time.
		The last example of the synthesis of a simple, stable molecule with the electronic configuration of antiaromaticity cyclooctatetraene —; was in 1913.
		It was thought that the cyclopentadienyl cation ought to be antiaromatic and hence unstable, because its electronic configuration corresponds to that predicted by theory to be antiaromatic.
	www.hinduonnet.com /thehindu/seta/2002/05/02/stories/2002050200070200.htm (257 words)

	In the Classroom (Site not responding. Last check: 2007-10-15)
		While the generalizations regarding aromatic (8n + 2) and antiaromatic (8n) contiguous nonfused bicycles are nicely supported at the Hückel level, there is a surprising feature.
		It is now clear that Hückel's rule, along with Breslow's extension of it, which were designed to describe annulenes, should not be applied to polycycles, even those as simple as bicycles.
		For example, a monocyclic structure which is antiaromatic (4n electrons) can easily have a planar nonaromatic bicyclic counterpart (e.g., 12 electrons).
	chemeducator.org /sbibs/s0003002/spapers/32lan897.htm (1300 words)

	CSIRO PUBLISHING - Australian Journal of Chemistry (Site not responding. Last check: 2007-10-15)
		Graph-theoretical arguments have produced an approach to generating antiaromatic hydrocarbon bicyclic structures.
		The newly recognized antiaromatic structures feature strategically located odd acyclic substituents.
		values are used to support the assignment of antiaromatic character to appropriate structures.
	www.publish.csiro.au /nid/51/paper/CH00089.htm (63 words)

	Hydrocarbon analogues of boron clusters [mdash] planarity, aromaticity and antiaromaticity (Site not responding. Last check: 2007-10-15)
		Hydrocarbon analogues of boron clusters [mdash] planarity, aromaticity and antiaromaticity
		Hydrocarbon analogues of boron clusters — planarity, aromaticity and antiaromaticity
		Aromatic boron clusters possess more circular shapes whereas antiaromatic boron clusters are elongated, analogous to structural distortions of antiaromatic hydrocarbons.
	www.nature.com /nmat/journal/v2/n12/abs/nmat1012.html (213 words)

	JCE 1996 (73) 899 [Sep] A Conceptually Simple Approach to the Analysis of Aromaticity in Pericyclic Transition States
		Other transition states are said to be analogous to aromatic or antiaromatic Möbius annulenes - which have each p-orbital in the "pi-system" tipped by an angle q with respect to each of its neighboring p-orbitals.
		Aromatic Möbius cyclobutadiene is shown to be an artifact of Hückel theory.
		It is then shown that transition states may be classified as aromatic / antiaromatic / non-aromatic by exploiting both the extent of orbital overlap which develops in competing transition states and Hückel's rule.
	jchemed.chem.wisc.edu:8000 /Journal/Issues/1996/Sep/abs899.html (243 words)

	Butalene and Related Compounds: Aromatic or Antiaromatic? (Site not responding. Last check: 2007-10-15)
		The first is planar and is judged "aromatic" by comparisons with suitable models using both energetic and magnetic criteria.
		The second is nonplanar, and not aromatic, but not so antiaromatic as cyclobutadiene (11).
		The third is slightly more antiaromatic and best viewed as a butalene fused to two cyclobutadiene rings; its properties are the sum of aromatic and antiaromatic components, like benzocyclobutadiene.
	pubs.acs.org /cgi-bin/abstract.cgi/jacsat/2001/123/i42/abs/ja011134v.html (151 words)

	A
		(3) The terms aromatic and antiaromatic have been extended to describe the stabilization or destabilization of transition states of pericyclic reactions.
		The hypothetical reference structure is here less clearly defined, and use of the term is based on application of the Hückel (4n + 2) rule and on consideration of the topology of orbital overlap in the transition state.
		Reactions of molecules in the ground state involving antiaromatic transition states proceed, if at all, much less easily than those involving aromatic transition states.
	www.chem.qmul.ac.uk /iupac/gtpoc/A.html (2527 words)

	Northwestern Observer Online
		The preparation of the cation and the solving of its X-ray structure are reported in the chemistry journal Angewandte Chemie.
		For certain electron configurations, however, delocalization lessens stability, and such molecules have been called antiaromatic.
		Lambert and Lin currently are studying the chemistry of the pentamethylcyclopentadienyl cation by carrying out reactions with the cation to learn more about its properties.
	www.northwestern.edu /univ-relations/observer/stories/05_16_02/cation.html (427 words)

	Chem 32 Virtual Manual (Site not responding. Last check: 2007-10-15)
		An antiaromatic compound does not obey the Hückel rule (4n+2 pi electrons in a closed cycle with a p orbital on every atom) and does not exhibit resonance stabilization.
		Unlike aromatic compounds, an antiaromatic compound is not flat, because to be flat would necessitate putting electrons in the high-energy antibonding orbitals of the aromatic configuration.
		To avoid this, the antiaromatic compound is typically buckled into a boat shape like cyclo-octatetraene, below:
	kalee.tock.com /chem32/org/18s.html (124 words)

	Energy Citations Database (ECD) - Energy and Energy-Related Bibliographic Citations
		Energy Citations Database (ECD) Document #6965209 - Study of antiaromatic biphenylenes and the repair of photodimerized bases in DNA
		Availability information may be found in the Availability, Publisher, Research Organization, Resource Relation and/or Author (affiliation information) fields and/or via the "Full-text Availability" link.
		Study of antiaromatic biphenylenes and the repair of photodimerized bases in DNA
	www.osti.gov /energycitations/product.biblio.jsp?osti_id=6965209 (100 words)

	Internet Electronic Journal of Molecular Design
		All interstellar ring molecules with π-electrons and their derivatives were found to be highly aromatic with large positive TREs.
		It seems quite likely that antiaromatic species are scarcely formed in interstellar space.
		This aspect of interstellar chemistry will be useful for designing or predicting unknown interstellar molecules.
	www.biochempress.com /av01_0052.html (136 words)

	[No title]
		A compound is Antiaromatic if Numbers (, (, and (are True, but (is False.
		Consider whether the four criteria in number 1 are true or false.
		Before we can apply this rule, the compound must have a _______________ ring of overlapping _____ orbitals, usually in a _________ arrangement.
	www.sunybroome.edu /~wovkulich_m/chm246/CHM246-U5-Worksheet.doc (1148 words)

	[No title] (Site not responding. Last check: 2007-10-15)
		Predict whether each of the following systems would be aromatic, antiaromatic, or nonaromatic.
		Assume each system is planar and justify your choice.
		Predict specific chemical or physical properties that would reveal the aromatic, antiaromatic, or non-aromatic character of the compound.
	webpub.alleg.edu /employee/s/smurphre/chem231/workshop/ws2s04.doc (599 words)

	Student Presentations at Regional, National, and International Meetings,Undergraduate research students are indicated ...
		Examination of the antiaromaticity of m-substituted diphenylmethylidenefluorene dications" Amber Rakowitz,* Nancy Mills, Michelle Benish, Lisa Bebell*
		National Meeting of the American Chemical Society, San Francisco, April 1-5, 2001, "Antiaromaticity of dialkyl-substituted fluorenylidene and indenylidene dications", Justin Mynar,* Nancy Mills, Ellen E. Burns.
		ABSTRACT ORGN 56."Further Investigation of Dications of Antiaromatic Compounds: Synthesis and Oxidation of 9-(4,4’-dimethyldibenzocyclohexyl)-9-H-Fluorene", Karen E. Unruh*, N. Mills, E. Burns.
	www.trinity.edu /nmills/text/Student-Presentations.htm (874 words)

	Undergraduate Research (Site not responding. Last check: 2007-10-15)
		In heterocyclic studies we have been concerned with the synthesis and properties of unusual rings containing metals or nitrogen as ring constituents.
		Illustrative are five-membered (borole) and seven-membered (borepin) boron rings, which display antiaromatic and aromatic character, respectively.
		Furthermore, nitrogen heterocycles isoelectronic with azulenes have been found to display chromoisomerism (tautomeric equilibira between colorless and highly colored isomers), and the highly reactive, antiaromatic dibenzazapentalene has been synthesized for the first time.
	chemistry.binghamton.edu /undergraduate/ugresearch.htm (9856 words)

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