Studies of 13C?H coupling constants: III—the conformational dependence of 1J(13CH) for the formyl proton in aromatic aldehydes

¹J(¹³CH) and ²J(¹³CH) involving the aldehydic proton in ortho-alkylbenzaldehydes have been examined for evidence of a hyperconjugative contribution from the aromatic π-electrons. The expected hyperconjugative effect is obscured by changes in the coupling constants resulting from steric inhibition of resonance.     

Infrared spectroscopy of CO on NaCl(100) IV. Bandshape analysis

The infrared bandshape of monolayer CO on NaCl(100) at 4 K is slightly asymmetric and its bandwidth of 0.09 cm⁻¹ is the narrowest observed for any surface molecule. From a variety of experiments we know that this band profile is determined by heterogeneous rather than homogeneous broadening. We offer an explanation for the experimentally observed bandshape by proposing that irregularities in the surface of the cleaved NaCl crystals give rise to many distinct two-dimensional domains of physisorbed CO. A first-order perturbation calculation, which generates the infrared cross-section as a function of domain size, has been used to estimate that on the order of 10⁵ molecules reside in an average size domain. The accuracy of the calculation, whose Hamiltonian represents the intermolecular potential among CO molecules by electric multipole coupling, will be discussed. We use the same coupling Hamiltonian to explore the effect of submonolayer coverages, isotopic dilution, and surface heterogeneities on the infrared spectroscopy of CO on NaCl(100). Our calculations can account for some, but not all, of the observed spectroscopic data.     

The area of the Mandelbrot set

Summary We obtain upper bounds for the area of the Mandelbrot set. An effective procedure is given for computing the coefficients of the conformal mapping from the exterior of the unit circle onto the exterior of the Mandelbrot set. The upper bound is obtained by computing finitely many of these coefficient and applying Green's Theorem. The error in such calculations is estimated by deriving explicit formulas for infinitely many of the coefficients and comparing.Partially supported by a grant from the National Science Foundation     

Optimal-order convergence rates for Eulerian-Lagrangian localized adjoint methods for reactive transport and contamination in groundwater

Eulerian–Langrangian localized adjoint methods (ELLAM) were developed to solve convection–diffusion–reaction equations governing contaminant transport in groundwater flowing through a porous medium, subject to various combinations of boundary conditions. In this article, we prove optimal-order error estimates and some superconvergence results for the ELLAM schemes. In contrast to many existing estimates for a variety of numerical methods, which often contain the temporal derivatives of the exact solution, our error estimates contain the total derivatives of the exact solution but do not involve any temporal derivatives of the exact solution. © 1995 John Wiley & Sons, Inc.     

An abnormal trend in J(13C?CH) values in some aldehydes

The ²J(¹³C? CH) couplings involving the formyl proton of α-halogeno-aldehydes have been found to decrease with increasing halogen electronegativity. This trend may be rationalised in terms of inductive withdrawal and a conformation dependent hyperconjugative effect. The direct J(¹³CH) couplings are also anomalous.     

Nanoelectrochemical analysis inside a single living cell

This critical opinion reviews the methods to construct and apply electrodes for analysis inside single cells and of single organelles. Nanoelectrochemical methodology, with an emphasis on nanoelectrode construction and analysis of metabolites, neurotransmitters, reactive oxygen and nitrogen species, glucose, oxygen, hydrogen peroxide, and ions in cells are discussed for measurements from cytoplasm to single organelles.     

Electronic structure and energetics of tetragonal SrCuO? and its high-pressure superstructure phase

First-principles calculations have been used to investigate the electronic structure and energetics of the simple tetragonal SrCuO? (P4=mmm) and its high-pressure tetragonal superstructure (P4=mmm). Based on the calculations, the high-pressure phase is metastable as compared with the low pressure tetragonal phase, with an energy difference of 0.13 eV per SrCuO? formula unit. The energy barrier to the transition from the superstructure to the simple tetragonal structure is 0.24 eV at 7 GPa; thus, high temperatures are required to synthesize the latter. Among the possible structural configurations resulting from the partially occupied oxygen site in the superstructure phase, the most stable structure has a space group PN4m2, reduced from that of the simple tetragonal structure P4=mmm. The detailed analysis of the electronic band structures of the simple tetragonal and superstructure phases suggests that the out-of-plane buckling of the O atoms in the superstructure leads to significant decrease in the O p-Cu d orbital overlap, allowing the energy of the system to be lowered, which is necessary for the structural stability. An understanding of the electronic structure and energetics of the high-pressure superstructure phase and its relation to the simple tetragonal phase provides a basis for exploring the physical properties of the infinite layer, high-TC superconductor.     

Collection method for chemical particulates on surfaces with detection using thermal desorption-ion trap mass spectrometry

Successful analysis of particulate/low vapor pressure analytes such as explosives and toxic chemicals, and commercial pesticides require new sampling tools that enable detection of these analytes using current vapor phase detection instruments. We describe a sampling approach that uses stainless steel screens coated with a sticky polydimethyl siloxane (PDMS) coating to capture particulates from surfaces. Preliminary results for the collection of dimethyl methylphosphonate (DMMP) sorbed onto silica gel (SG) particulates (DMMP/SG) from a surface with subsequent analysis by thermal desorption-cylindrical ion trap mass spectrometry (TD-CITMS) are reported.