A facile synthesis of primary amines from carboxylic acids by the curtius rearrangement

2-Trimethylsilylethanol was used to trap isocyanates produced by the Curtius rearrangement of acyl azides and the resulting trimethylsilylethyl carbamates were readily cleaved with tetra-n-butylammonium fluoride to liberate the primary amines.     

Numerical continuation of degenerate homoclinic orbits in planar systems

In this paper we develop numerical algorithms for the continuationof degenerate homoclinic connections in planar systems. We considerthe case where the equilibrium point has zero trace and twocases of higher-order degeneracies. The method we propose isable to continue homoclinic connections of order up to codimension-four.Application of the algorithm to four examples supports its validityand demonstrates its usefulness.     

Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.     

The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.     

Uniform molecular analysis using femtosecond laser mass spectrometry

The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd.     

Synthesis of deuterium-labeled derivatives of dimethylallyl diphosphate

Short practical syntheses for five deuterium-labeled derivatives of dimethylallyl diphosphate (DMAPP) useful for enzymological studies are reported. These include the preparation of the C1-labeled derivatives (R)-[1-2H]3-methylbut-2-enyl diphosphate ((R)-[1-2H]1-OPP) and (S)-[1-2H]3-methylbut-2-enyl diphosphate ((S)-[1-2H]1-OPP), the C2-labeled derivative [2-2H]3-methylbut-2-enyl diphosphate ([2-2H]1-OPP), and the methyl-labeled derivatives (E)-[4,4,4-2H3]3-methylbut-2-enyl diphosphate ((E)-[4,4,4-2H3]1-OPP) and (Z)-[4,4,4-2H3]3-methyl-but-2-enyl diphosphate ((Z)-[4,4,4-2H3]1-OPP).     

Intersubband transitions in InAs/GaSb semi-metallic superlattices

Magnetic field orientated parallel to the superlattice layers enables intersubband absorption to occur for normally incident light. We investigate semi-metallic InAs/GaSb superlattices in this configuration, presenting data over a wide range of InAs well widths. For narrow wells, the reduced absorption coefficient means that an alternative waveguide configuration, where the light makes about 4 or 5 passes through the sample is used. In this second configuration we see further activation of the intersubband resonance by the parallel field. The intersubband energy and absorption characteristics are studied over a large range of well widths and compared with results from 8-band k·p calculations.