NMR solvent shifts and structure elucidation in coumarins

The use of the solvent shift techniques enables the position of methyl, methoxyl and aromatic protons in coumarins to be determined and should prove a valuable aid to structural elucidation in this class of compounds.     

Theories whose resplendent models are homogeneous

Buechler proved that ifT satisfies certain conditions, then all resplendent models ofT are homogeneous. Here the theories whose resplendent models are all homogeneous are characterized as satisfying a pair of conditions (weaker than Buechler’s). It follows from the characterization that if all resplendent models ofT in some uncountable power are homogeneous, then all resplendent models ofT are homogeneous. The author thanks John Baldwin and the other participants in the 1979 and 1980 Forking Festivals for helping her to learn some stability, and especially, Steve Buechler, whose results led directly to the results of this paper. Research partially supported by the National Science Foundation under Grant MCS78-02224.     

The photochemistry of citral

Citral (I) is cyclized by UV irradiation¹ to 2-isopropenyl-5-methylcyclopentane-carboxaldehyde (II), containing the carbon skeleton of the monoterpenes of ants and catmint. 1,6,6-Trimethylbicyclo[2,1,1]hexane-2-carboxaldehyde (XII, R = H), produced in lesser amount at the same time, was synthesized from camphor. The two photocitrals may, perhaps, come from a common intermediate containing the cyclopentane ring.     

Harmonic coincidences between cw gas laser lines for extending frequency measurements to the 10μm wavelength region

Wavelength and frequency data for far-infrared c.w. gas laser lines have been scanned using a computer for chains of harmonic coincidences suitable for transferring frequency measurements from the submillimetre to the 10m wavelength region. A table of selected possibilities using up to three lasers in sequence is presented showing the calculated beat frequencies.     

Elimination reactions in dimethyl sulfoxide solution. The effective base with potassium tert-butoxide.

Deuterium labeling studies have established that elimination of a cyclooctylammonium iodide with dimsyl anion in DMSO proceeds through an ylide intermediate while elimination with KOC(CH₃)₃ in DMSO involves an E2 mechanism. The effective base with KOC(CH₃)₃/DMSO is shown to be the alkoxide ion.     

Evidence for a Ag adatom-molecule complex in surface enhanced raman scattering

The SERS spectrum of molecules adsorbed on Ag sols show, lines, in the 200–300 cm^?1 region in the absence of Cl^? ions These lines are attributed to a Ag-N complex and frequency calculations show that they correspond to the vibrations of the molecule bound to a single silver atom.     

Frequency doubling of a fibre-amplified 1083 nm DBR laser

A good frequency standard is required at 1083 nm for measurements on the fine structure of helium and of the fine structure constant. Several milliwatts of CW frequency-doubled light offers the prospect of stabilisation to a Doppler-free hyperfine transition in molecular iodine. The 1083 nm emission of an extended-cavity DBR diode laser has been amplified using an ytterbium-doped fibre amplifier, and applied to a type-I phase matched Mg:LiNbO₃ crystal in a high-Q fundamental-resonant cavity for frequency doubling. The amplifier gain at 1083 nm under typical operating conditions was 13.8 dB, with a coherent output power up to 63 mW, limited by the maximum signal input power. The doubling cavity Q was , and about 70% of the incident power was coupled in. The maximum 2nd-harmonic conversion efficiency exceeded 20% and provided an output power of 3.7 mW for making continuous frequency scans of up to 600 MHz in the green. An optical spectrum analyser at 541.5 nm showed fringes of 4.6 MHz full width half maximum, close to the instrumental width. Received: 25 February 1998 / Revised and Accepted: 28 May 1998     

Assessment of structural analysis technology for static collapse of elastic cylindrical shells

The prediction of the ultimate load-carrying capability for compressively loaded shell structures is a challenging nonlinear analysis problem. Selected areas of finite element technology research and nonlinear solution technology are assessed. Herein, a finite element analysis procedure is applied to four cylindrical shell collapse problems which have been used by computational structural mechanics researchers in the past. This assessment will focus on a number of different shell element formulations and on different approaches used to account for geometric nonlinearities. The results presented confirm that these aspects of nonlinear shell analysis can have a significant effect on the predicted nonlinear structural response. All analyses were performed using a single software system which allowed a convenient assessment of different element formulations with a consistent approach to solving the discretized nonlinear equations.