The stacking of 4n pi electron hydrocarbon rings into superphane structures can eliminate their antiaromaticity and result in through-space three-dimensional aromatic character. This is demonstrated by the bond length equalized geometries and diatropic NICS values of the methano-bridged superphane series with interacting three- to nine-membered 4n pi electron rings. Along with triplet and Möbius strategies, stacking is the third way to achieve aromatic ring systems with 4n pi electrons.

Monocyclic [11]annulenium cations, which are experimentally unknown, have been studied primarily via DFT methods but also with some CCSD(T) validation. We have located six minima: two doubly trans (26, 27), one triply trans (28), one singly trans (29), one quintuply trans (trannulene-type, 33), and one all-cis (31). The first three are aromatic, 33 is modestly aromatic, 29 is nonaromatic, and the last is a Möbius antiaromatic species. We also investigated the fusion of various numbers of three-membered rings (3MRs) to the central 11-membered ring (11MR). We found several planar, all-cis-[11]annulenium ion derivatives as well as another Möbius antiaromatic species (52b); for comparison, we also found planar, antiaromatic all-cis-[12]annulene (60) and [15]annulenium cation (61) derivatives. The (anti)aromatic characterization of these compounds is based mainly on calculated magnetic data for the ground singlet and vertical triplet states, although aromatic stabilization energies (ASE) are also considered. Data for optimized triplets, several of which are Möbius aromatic systems (31t, 52t, 63t, 64t), are also included. Several of these cations are reasonable synthetic targets.

A series of aryl amines was found to induce cleavage of DNA. Subsequent refinement led to an efficient family of dimeric derivatives capable of cleavage at low concentration. Initial investigations suggest this is an unprecedented mode of DNA cleavage, which may be ultimately applied to the development of sequence-specific agents.

The electronic structure of the transition state for the cyclopropylidene to allene conversion has been probed. The methodology involved the relative rates of ring opening vs trapping by MeOH for a series of variously substituted 2,3-diarylcyclopropylidenes. With the assumption that the rate of trapping was unaffected by substituents, a Hammett correlation was constructed. The negative value (-0.72) for rho indicated that the carbenic center attracts electron density in the ring-opening transition state, much like the cyclopropyl cation to allyl cation transition state. Temperature-dependent studies showed that the observed preference for ring opening was driven by entropy factors. Also, using reasonable estimates for the close to diffusion-controlled trapping activation enthalpies, the derived enthalpies for ring opening were in close agreement with the best theoretical values.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHomoaromatic delocalization in the transition state for norcaradiene formationAchim. Bertsch, Wolfram. Grimme, Gerd. Reinhardt, Hermann. Rose, and Philip M. WarnerCite this: J. Am. Chem. Soc. 1988, 110, 15, 5112–5117Publication Date (Print):July 1, 1988Publication History Published online1 May 2002Published inissue 1 July 1988https://doi.org/10.1021/ja00223a033RIGHTS & PERMISSIONSArticle Views308Altmetric-Citations10LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (825 KB) Get e-Alertsclose Get e-Alerts

AbstractThe kinetics of the extrusion of benzene (II) from the adducts (I) are measured.

The preparation of bicyclo [2.2.0]hex- 1(4)-ene ( 1 ) via ring expansion of a cyclopropylcarbene or the dehalogenation of 1-bromo-4-chlorobicyclo[2.2.0]hexane is described. It is one of the most reactive of the alkenes which may be observed at room temperature. Its reactions, including dimerization and cycloaddition reactions, are described. The latter lead to convenient preparations of [m.2.2]propellanes. The vibrational spectrum was examined via matrix isolation and ab initia MO calculations.

AbstractDas Olefin (I) wird mit Ozon zu (IIa) gespalten und anschließend reduziert.

Solution thermolysis of the epimers 5 gave rise to separate sets of products, including, for one, Skattebol-type rearrangement. However, neither epimer produced a free carbene.

It is shown that a recent claim for the intermediacy of a carbene alkene complex is unsubstantiated. An alternative mechanism is proposed.

The title compound has been synthesized in several steps from [4.3.1]propell-3-ene; it thermally provides 1,3-divinylcyclohexene.

Strain energy calculations (MM2) are reported for 36 bridged dienes; the relationship between strain energy and stability is discussed.

The synthesis of 3 dithiapaddlanes is described.

The carbonic dimers of some tricyclic cyclopropylidenoids have been isolated. The X-ray structure of one (12) has been determined. These are derivatives of tetra-t-butylethylene (1).