Nucleus-independent chemical shifts (NICS) have been used extensively for the identification of aromaticity properties molecules, ions, intermediates, and transition states since their introduction in 1996 by Schleyer et al. Initially, probes (bq's) were placed at centers systems (NICS(0)) later, 1Å above molecular planes (NICS(1)). However, contradicting assignments NICS other methods found some systems. In this article, an alternative NICS-based method is introduced. The based on scanning...

Abstract Nucleus‐independent chemical shift (NICS)‐based methods are very popular for the determination of induced magnetic field under an external field. These used mostly (but not only) aromaticity and antiaromaticity molecules ions, both qualitatively quantitatively. The ghost atom that serves as NICS probe senses reports it in form NMR shift. However, source cannot be determined by NICS. Thus, a multi‐ring system may contain more than one current circuit (and therefore field) value...

Aromaticity has been a basic concept in chemistry for many years, yet it is poorly understood. This Feature Article introduces some questions regarding the concept, describes major paradigms field, and emphasizes contradictions paradoxes between these paradigms, different measures of aromaticity.

A model for obtaining the σ-only effect on nucleus-independent chemical shift (NICS) is introduced. By subtracting values obtained "σ-only" from respective of conjugated system it possible to obtain NICS that originate π only. This procedure allows a quantitative measure relative intensities diatropic and paratropic ring currents in different systems with built-in their accuracy. The scope limitations are discussed.

Three series of stable, neutral, π-extended bispentalene derivatives, with two pentalenes fused to a central benzene or naphthalene moiety, have been prepared through modified double carbopalladation cascade reaction. While these chromophores feature skeletons [4n+2] π-electron perimeters, the 8 pentalene subunits strongly influence bonding and spectral properties. 1H NMR spectra showed large upfield shifts protons in moieties, comparable antiaromatic monobenzopentalenes. Further...

The Nucleus Independent Chemical Shift (NICS) method was invented in 1996 by the late Paul v. R. Schleyer as a computational tool for assessment of aromaticity. In intervening years, NICS has developed considerably. This Minireview describes NICS‐based methods that are currently available and concludes with recommendations choosing appropriate to study given problem.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIs the Mills Nixon effect real?Amnon StangerCite this: J. Am. Chem. Soc. 1991, 113, 22, 8277–8280Publication Date (Print):October 1, 1991Publication History Published online1 May 2002Published inissue 1 October 1991https://pubs.acs.org/doi/10.1021/ja00022a012https://doi.org/10.1021/ja00022a012research-articleACS PublicationsRequest reuse permissionsArticle Views944Altmetric-Citations118LEARN ABOUT THESE METRICSArticle Views are COUNTER-compliant...

When close to the molecular plane, behavior of nucleus independent chemical shift (NICS) as a function distance from plane deviates its at larger distances. By using dense grid NICS-probes (BQs) it is shown that, when maximal (absolute) NICS values are obtained above atoms. These maxima move towards center elevated until maximum and stay there further elevated. It that this result current density, which influenced by electron according Biot-Savart law, which, in turn, causes induced magnetic...

Cyclopentadiene derivatives with electronegative (F, Cl) or electropositive (H(3)Si, Me(3)Si) bis-5,5-substituents were studied at the B3LYP/6-311G* level of theory. It was found that there is no special stabilization destabilization for any derivatives; energetic effects previously attributed to aromatic antiaromatic are result interactions in reference systems. A nucleus-independent chemical shift (NICS) scan study HF-GIAO/6-311+G* theoretical these and similar suggest they all show...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNovel route to carbon-silicon double bonds via a Peterson-type reactionDmitry Bravo-Zhivotovskii, Viviana Braude, Amnon Stanger, Moshe Kapon, and Yitzhak ApeloigCite this: Organometallics 1992, 11, 7, 2326–2328Publication Date (Print):July 1, 1992Publication History Published online1 May 2002Published inissue 1 July 1992https://pubs.acs.org/doi/10.1021/om00043a003https://doi.org/10.1021/om00043a003research-articleACS PublicationsRequest reuse...

The aromaticity of oligomers predicts their HOMO–LUMO gaps and ionization potentials.

Applying fine grids of nucleus independent chemical shift (NICS) probes (BQs) at different distances from the molecular plane aromatic and antiaromatic molecules suggests that, short distances, NICSπ,zz is maximal (absolute values) off geometrical center systems. In nonsymmetric systems, induced ring current may be a little center, but difference negligible ≥2 Å. At these change with distance follows power relation. It shown that order diatropicity paratropicity within group depends on...

The copper-catalyzed carbomagnesiation (or hydrometalation) reaction of chiral cyclopropenylcarbinol derivatives, obtained by means a kinetic resolution secondary allylic alcohols, leads to an easy and straightforward preparation enantiomerically pure alkylidenecyclopropane derivatives. mechanism is composed syn-carbometalation followed syn-elimination reaction. To gain further insight into the carbometalation, diastereoselective formation cyclopropylcarbinol was also achieved found be very...

The zinc-catalyzed addition of various alkynes to acylsilanes followed by a Zn-Brook rearrangement and either the Zn-ene-allene or Zn-yne-allene cyclization led enantio- diastereoselective formation carbocycles in single-pot operation.

Abstract The magnetic response of a set 20 molecules, their dications and dianions has been studied by the NICS‐ XY method, results have compared with first principles current density maps. molecules built from pentalene s ‐indacene single double annulation cyclobutadiene, benzene benzocyclobutadiene in an alternate fashion on both sides molecules. prediction tropicities obtained method are overall consistent A literal code, developed to give compact description currents flowing around rings...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAre carbenium ions stabilized or destabilized by .alpha.-silyl substitution? The solvolysis of 2-(trimethylsilyl)-2-adamantyl p-nitrobenzoateYitzhak Apeloig and Amnon StangerCite this: J. Am. Chem. Soc. 1985, 107, 9, 2806–2807Publication Date (Print):May 1, 1985Publication History Published online1 May 2002Published inissue 1 1985https://doi.org/10.1021/ja00295a043Request reuse permissionsArticle Views147Altmetric-Citations52LEARN ABOUT THESE...

Aromaticity is a fundamental concept in organic chemistry that has gradually been extended to many other areas the chemical sciences, including organometallic chemistry. By replacing CH unit an aromatic hydrocarbon (e.g., benzene) with fragment, novel metallaaromatic compounds intriguing physicochemical properties can be synthesized. Yet, despite intense research efforts, synthesis of their macrocyclic congeners remains challenging, mainly due lack straightforward synthetic strategies. Here...

Strain-induced bond localization (SIBL) has been a debated issue for almost 70 years. In the past decade there have some developments that showed strain can indeed localize aromatic bonds. However, compounds should exhibited positive ΔR (Mills−Nixon distortion) instead negative (anti-Mills−Nixon distortion), apparently more coherent with π effects (aromaticity−antiaromaticity arguments). Using ab initio methods, structure of cyclopropabenzenes, cyclobutabenzenes, and benzocyclobutadienes,...

The regioselectivity of the oxidation alpha-tocopherol (the main component vitamin E) to an ortho-quinone methide (oQM) has been explained in literature mostly by ill-defined term "Mills-Nixon effect". In this paper we describe preparation eleven derivatives, different from each other sum annulation angles, but keeping electronic factors unchanged. These compounds underwent Ag(2)O oxidation, forming two isomeric oQMs that were trapped vinylmethyl ether. It was found product ratio changes...

[reaction: see text] The total synthesis of C(3)(h)-symmetric [7]phenylene has been accomplished by triple cobalt-catalyzed cycloisomerization an appropriate nonayne. Its spectral data are in accord with the expectations for a triply angularly fused system, but its calculated heat formation suggests presence destabilizing sigma effect relative to D(3)(h) isomer. molecule constitutes largest substructure archimedene hitherto synthesized.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe first demonstration of solvolytic generation a simple silicenium ion (R3Si+). Access via 1,2-methyl migrationYitzhak Apeloig and Amnon StangerCite this: J. Am. Chem. Soc. 1987, 109, 1, 272–273Publication Date (Print):January 1987Publication History Published online1 May 2002Published inissue 1 January 1987https://pubs.acs.org/doi/10.1021/ja00235a041https://doi.org/10.1021/ja00235a041research-articleACS PublicationsRequest reuse...

Abstract What is the nature of CC bond? Valence bond and electron density computations 16 bonds show two families that flesh out as a phase diagram. One family, involving ethane, cyclopropane so forth, typified by covalent bonding wherein spin‐pairing accounts for most energy. The second family includes inverted bridgehead small propellanes, where neither nor ionic, but owes its existence to resonance stabilization between respective structures; hence charge‐shift (CS) bond. dual also...