Aromaticity and antiaromaticity in zintl clusters liu. Annulenes, monocyclic conjugated ions, and annulenoannulenes. Nonaromatic definition of nonaromatic by merriamwebster. Dec 15, 2016 first experimental evidence of 3d aromaticity in stacked antiaromatic compounds date. If its a planar structure it has an energetic penalty antiaromaticity for being so. In addition, label each compound as aromatic, antiaromatic or nonaromatic nonaromatic. Apr 08, 2015 what classifies a compound as aromatic, nonaromatic, or antiaromatic. All three predicted lowlying isomers of nasi 4 were produced experimentally and characterized by photoelectron spectroscopy figure4. Antiaromaticity ronald breslow mitchill professor of chemistry, columbia university, newyork, york 10027 received march 12, 1973 aromaticity isa word with many meanings. First experimental evidence of 3d aromaticity in stacked. Thomas heine, clemence corminboeuf, and, gotthard seifert.
The discovery of the facile splitting of molecular hydrogen shows the inherent instability of the unsaturated borole systems and demonstrates. Quantitative assessment of aromaticity and antiaromaticity. Thus, it represents the electronic structure in terms of nc 2e bonds. Dec 04, 2016 aromaticity antiaromaticity non aromaticity 1. Aromaticity although the name aromatic was originated from the characteristic odour or aroma of benzene. Chem 242 spring 2008 answers to problem set 4 question 1. The mobius strip, with its fascinating structure, was first discovered by august ferdinand mobius and johann benedict listing in 1858 1. Homoaromaticity, in organic chemistry, refers to a special case of aromaticity in which conjugation is interrupted by a single sp 3 hybridized carbon atom.
May 18, 2018 originally, the concepts of aromaticity and antiaromaticity were introduced to explain the stability and reactivity of unsaturated organic compounds. Measuring antiaromaticity by an analysis of ring current and coupling constant changes in a cyclopentadienonefused dihydropyrene. Determining aromaticity, non aromatics, and antiaromatics. Antiaromaticity is a characteristic of a cyclic molecule with a. A cyclic compound with delocalized electrons that does not obey huckels rule, and is much less stable than similar nonaromatic compounds explanation of antiaromaticity. Antiaromatic compound an overview sciencedirect topics. First experimental evidence of 3d aromaticity in stacked antiaromatic compounds 15 december 2016 antiaromatic planar norcorrole molecules form close. Mobius aromaticity and antiaromaticity in expanded porphyrins. As noted above, 1,3,5,7cyclooctatetraene is nonplanar and adopts a tubshaped conformation. Adndp is based on the concept of the electron pair as the main element of chemical bonding models. Researchers found that antiaromatic planar norcorrole. Aromaticity and antiaromaticity in transitionmetal systems.
Recent findings of aromaticity and antiaromaticity in allmetal clusters have stimulated further research in describing the chemical bonding, structures and stability in transitionmetal clusters. Boldyreva received 5th september 2007, accepted 17th october 2007. This investigation is based on qualitative theory, quantum chemical qc calculations and experimental work. Pdf aromaticity and antiaromaticity in transitionmetal systems. Effect of transition state aromaticity and antiaromaticity on. Cyclooctatetraene is floppy enough to be able to bend out of the plane. Antiaromatic compounds are not necessarily unstable they are just less stable than a bunch of ethenes connected by sigma bonds. Antiaromaticity article about antiaromaticity by the free. Aromatic, antiaromatic, or nonaromatic compounds chemistry. Pdf aromaticity, antiaromaticity, homoaromaticity and.
In short, the only way aromatic and antiaromatic compounds differ is the number of electrons they have in the conjugated system. Annulenes, barrelene, aromatic ions and antiaromaticity. In analogy with the matrix isolation and characterization of thiirene and selenirene, a number of fivemembered heterocyclic isomers of type 62ae were irradiated at 1015 k to produce the thermally labile nitrile sulfides 63 scheme 10, most probably through the intermediacy of the threemembered ring thiazirenes 2. The antiaromaticity of boroles is well reflected in their chemical reactivity, which is dominated by many types of addition reactions, such as, inter alia, cycloadditions and reactions with nucleophiles. Aromaticity and antiaromaticity in zintl clusters article in chemistry a european journal 2455 may 2018 with 54 reads how we measure reads. Multiple aromaticity and antiaromaticity in silicon clusters. Not being aromatic does not necessarily make the molecule unstable. Kraka, and dieter cremer 4 computational and theoretical chemistry group catco, department of chemistry, southern methodist university, 3215 daniel. A compound whose molecule contains one or more aromatic rings is called an aromatic compound. Such regrettable imprecision is thus cause for caution although it is hardly a reason to discard.
Although this sp 3 center disrupts the continuous overlap of porbitals, traditionally thought to be a requirement for aromaticity, considerable thermodynamic stability and many of the spectroscopic, magnetic, and chemical properties. Kraka, and dieter cremer computational and theoretical chemistry group catco, department of chemistry, southern methodist university, 3215 daniel. Averkiev,a huajin zhai,b laisheng wangbc and alexander i. Since then, they have been extended to other species with delocalized electrons including various saturated systems, organometallic compounds, and even inorganic clusters and molecules. And lastly, keep in mind that being aromatic is not a requirement for stability. Recent developments in the chemistry of antiaromatic boroles. There are chemical and spectroscopic methods that can be used to experimentally determine whether a ring is aromatic or not.
Provide molecular orbital diagrams for each of the following compounds. Effect of transition state aromaticity and antiaromaticity on intrinsic barriers of proton transfers in aromatic and antiaromatic heterocyclic systems. Information and translations of antiaromaticity in the most comprehensive dictionary definitions resource on the web. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. Aromatic ions and antiaromaticity chemistry libretexts. Adaptive natural density partitioning adndp 1 is a newly developed theoretical tool for obtaining patterns of chemical bonding in the systems of the most general type.
However, besides the fundamental aspects of the electronic structure and reactivity, boroles have not encountered serious research efforts for a rather long timeframe. We talked about aromatic and antiaromatic compounds which are recognized based on the huckels rule. Cyclobutadiene and cyclopentadienyl cation two examples of antiaromatic compounds are not floppy enough to bend out of plane. And even though there might be nonaromatic compounds that are particularly stable, as a general statement it would only relater to antiaromatic compounds. What is the difference between antiaromatic and non. If the pi electrons in an antiaromatic compound were to delocalize across a large degenerate orbital, then the result would be a half filled shell. Aromaticity and antiaromaticity in transitionmetal systems dmitry yu. All the other criteriabeing cyclic, planar and fully conjugated are a must for both categories. In organic chemistry, aromaticity is a property of cyclic ringshaped, planar flat structures with a ring of resonance bonds that gives increased stability compared to other geometric or connective arrangements with the same set of atoms. Journal of the american chemical society 2005, 127 46, 1625116254. Content 1aromatic compaund 2criteria for aromaticity 3difference between aromatic, antiaromatic,nonaromatic 4aromatic hetrocyclic compound 5annulene 2. First isolated in 1969, most progress in the chemistry of the antiaromatic 4. Aromaticity and antiaromaticity in zintl clusters request pdf. Cyclic congugation increases the number of p orbital interactions in the conjugated system, stabilizing the pi bonds.797 1331 411 1342 377 471 1061 1352 511 750 801 469 312 1376 1488 843 260 1248 1448 783 1 1477 881 504 491 784 189 1059 855 626