Trapping rhodium vinylcarbenoids with aminochalcones for the synthesis of medium-sized azacycles

A rhodium carbenoid initiated cascade has been developed for the stereoselective synthesis of medium-sized azacycles. The cascade approach utilizes readily accessible N-benzyl protected aminochalcones and vinyldiazo compounds to access 9-membered azacycles through a carbene- nitrogen insertion/aldol/oxy-Cope sequence. The cascade reaction has proven general with a range of N-benzyl protected aminochalcones and vinyldiazos to provide diverse medium-sized azacycles.     

Theoretical structure and surface energy of the reconstructed {01.2} form of calcite (CaCO3) crystal

Two different reconstructions of the (01.2) face (Ca or CO₃ terminated) of calcite (CaCO₃) were studied: (i) R1 reconstruction: the outermost layer is based on the [0 1 0] × 1/3[2 1 1] rectangular mesh, which is symmetrical with respect to the c glide plane of the crystal, thus fulfilling the 2D symmetry of the face and (ii) R2 reconstruction: the outermost layer is based on a lozenge shaped mesh that does not respect the 2D symmetry of the face.The , , and slabs geometry optimizations of calcite (CaCO₃) were performed either at DFT level or by using empirical potentials; the results obtained with these two different calculation methodologies are in good agreement. With respect to their arrangement in the bulk, the CO₃ groups of the outermost layer are significantly rotated about the crystallographic a-axis and about the normal to the 01.2 plane; further, the thickness of the outermost layer is significantly lower than that of the underneath ones.The surfaces energies (γ) at 0 K, for relaxed and unrelaxed , , and faces, were determined either at DFT level or by using empirical potentials. Independently of the method of calculation employed, the stability order of the relaxed faces is < < < . Concerning the unrelaxed faces, whose energies were evaluated by using empirical potentials only, the stability order is instead < < < ; such different ordering shows the importance of geometry relaxation in the calculation of the surface energy. The values of the relaxed surface energies are , , and erg/cm².     

The reactions K−p → π∓Σ± at 4.2 GeV/c

We present differential cross sections and the Σ⁺ polarization for the reactions K^?p → π^?Σ^± using data from a high statistics bubble chamber experiment at 4.2 GeV/c incident momentum. The statistical level allows a detailed analysis of these reactions over the whole t range. Several significant structures are observed. Comparisons are made with SU(3)-related reactions; for backward production of π^?Σ⁺ such a comparison shows good evidence for Δ exchange. The exotic forward peak in K^?p → π⁺Σ^? is definitely confirmed.     

Non-strange vector meson production in K−p interactions at 4.2 GeV/c

The vector meson production, hypercharge exchange reactions K^?p → (φ, ω, ?) Λ and (φ, ?) Σ⁰ are studied at 4.2 GeV/c incident momentum. The data come from a high statistics bubble chamber experiment with a sensitivity of ～ 120 events/μb. Total and differential cross sections are presented. The vector meson density matrix elements and hyperon polarization are investigated as functions of momentum transfer. Amplitude analyses are performed for all five reactions. The results are compared with duality and quark model predictions, as well as used to test current ideas in two-body phenomenology.     

Theoretical investigation of the photophysics of methyl salicylate isomers

The photophysics of methyl salicylate (MS) isomers has been studied using time-dependent density functional theory and large basis sets. First electronic singlet and triplet excited states energies, structure, and vibrational analysis were calculated for the ketoB, enol, and ketoA isomers. It is demonstrated that the photochemical pathway involving excited state intramolecular proton transfer (ESIPT) from the ketoB to the enol tautomer agrees well with the dual fluorescence in near-UV (from ketoB) and blue (from enol) wavelengths obtained from experiments. Our calculation confirms the existence of a double minimum in the excited state pathway along the O-H-O coordinate corresponding to two preferred energy regions: (1) the hydrogen belongs to the OH moiety and the structure of methyl salicylate is ketoB; (2) the hydrogen flips to the closest carboxyl entailing electronic rearrangement and tautomerization to the enol structure. This double well in the excited state is highly asymmetric. The Franck-Condon vibrational overlap is calculated and accounts for the broadening of the two bands. It is suggested that forward and backward ESIPT through the barrier separating the two minima is temperature-dependent and affects the intensity of the fluorescence as seen in experiments. When the enol fluoresces and returns to its ground state, a barrier-less back proton transfer repopulates the ground state of methyl salicylate ketoB. It is also demonstrated that the rotamer ketoA is not stable in an excited state close to the desired emission wavelength. This observation eliminates the conjecture that the near-UV emission of the dual fluorescence originates from the ketoA rotamer. New experimental results for pure MS in the liquid state are reported and theoretical results compared to them.