A novel approach towards intermolecular stabilization of para-quinone methides. First complexation of the elusive, simplest quinone methide, 4-methylene-2,5-cyclohexadien-1-one

A novel approach towards the intermolecular stabilization of "simple" (i.e. methylene-unsubstituted) p-quinone methides (QMs) by their coordination to a transition-metal center is described. 4-Bromomethyl phenols, protected by a silyl group, were employed as the QM precursors and cis-chelating diphosphine Pd0 complexes were chosen as the metal precursors, since they have strong back-bonding interactions with the electron-poor QM moiety. Removal of the silyl protecting-group from the corresponding [LPd(benzyl)Br] complex (L=bisphosphine) with fluoride results in the spontaneous rearrangement of the unobserved zwitterionic Pd(II) complex into the QM-Pd0 complex. The feasibility of this approach was demonstrated in the synthesis of the structurally characterized Pd0 complex of BHT-QM (4), a biologically relevant metabolite of 2,6-di-tert-butyl-p-cresol, and the synthesis of the complex of 4-methylene-2,5-cyclohexadien-1-one (11), the simplest, and so far unobserved QM molecule. These complexes exhibit a remarkable thermal stability and do not react with alcohol or water. In both cases, the use of an appropriate incoming ligand allowed the release of the coordinated QM into the reaction media in which it was effectively trapped by added nucleophiles.     

Far-infrared spectroscopy of small neutral silver clusters

The vibrational spectra of Ag(3) and Ag(4) are recorded in the far-infrared between 100 and 220 cm(-1) using multiple photon dissociation spectroscopy of their complexes with Ar atoms. For Ag(3)-Ar two IR active bands are found at 113 and 183 cm(-1), for Ag(4)-Ar one band at 163 cm(-1) and very weak IR activity at 193 cm(-1) are observed. This, together with recent theoretical studies, allows for a reassignment of the controversial vibrational data reported earlier for the bare Ag(3) cluster. The influence of the number of Ar atoms in the complexes on the frequency of the IR active modes is found to be minor. However, the low-frequency IR-active band of Ag(3) shifts with increasing Ar coverage from 113 cm(-1) for Ag(3)-Ar to about 120 cm(-1) for Ag(3)-Ar(4), the value known for Ag(3) embedded in rare gas matrices.     

Topics in Noncommutative Geometry Inspired Physics

In this review article we discuss some of the applications of noncommutative geometry in physics that are of recent interest, such as noncommutative many-body systems, noncommutative extension of Special Theory of Relativity kinematics, twisted gauge theories and noncommutative gravity.     

Pd/C-catalyzed alkynylation of β-chloroacroleins

The first Pd/C-mediated Sonogashira coupling of β-chloroacroleins with terminal alkynes is described here. Pd/C–CuI–PPh₃ was found to be an efficient catalyst system for this coupling reaction. Using this economic and general process a variety of 4-alkynyl-2H-chromene-3-carbaldehydes and 5-alkynyl-2,3-dihydro benzo[b]oxepine-4-carbaldehydes were prepared in good yields.     

Shell effects in singly and multiply charged silver and gold clusters

The mass spectra of silver- and gold-clusters, generated by a gas aggregation technique and ionized by electron impact, reveal anomalies in the relative abundance of both singly and multiply charged clusters. Concentration maxima for singly charged species Ag _n ⁺ and Au _n ⁺ (n=3, 9, 19, (21), 35) are in agreement with experimental data of Katakuse and the predictions from the electronic shell model. The observed anomalies in the abundance spectra of doubly charged silver and gold clusters as well as triply charged silver cluster ions are explained in terms of electronic shell closing.     

Observation of a four-pion vector-meson state of mass ≈ 1.5 GeV produced by linearly polarized 9.3 GeV photons

From a study of γp → 2π⁺2π⁻p using 9.3 GeV linearly polarized photons, evidence is found for a J^P = 1⁻, I^G = 1⁺ four pion enhancement of mass ∼ 1.5 GeV with a production cross section of 1.6 ± 0.4 μb.     

Supertori are algebraic curves

Super Riemann surfaces of genus 1, with arbitrary spin structures, are shown to be the sets of zeroes of certain polynomial equations in projective superspace. We conjecture that the same is true for arbitrary genus. Properties of superelliptic functions and super theta functions are discussed. The boundary of the genus 1 super moduli space is determined.Research partially supported by the DOE (DE-AC02-82-ER-40073) and NSF (PHY-85-21588)