In-situ sensing of tropospheric water vapor using an airborne near-IR diode laser hygrometer

12 molecules cm^-3 Hz^-1/2 (signal-to-noise ratio 3). This is equivalent to a mixing ratio of 0.3 ppmv at average midlatitude tropopause conditions or a mixing ratio of 0.6 ppmv under boundary-layer conditions. The corresponding minimum measurable absorbance is 10^-5 Hz^-1/2. The laser hygrometer was field-demonstrated aboard the NASA P3B research aircraft, during a series of flights spanning several weeks in the summer of 1997. During this demonstration, the laser hygrometer was intercompared with two optical chilled mirror hygrometers. In general, the laser hygrometer performed well; however, under some conditions, it reported water vapor number densities 20% greater than the cryogenic frost-point hygrometer. This difference is currently under study. Received: 31 March 1998/Revised version: 3 June 1998     

Triple asymmetric synthesis for fragment assembly: Validity of approximate multiplicativity of the three diastereofacial selectivities

A strategy of triple asymmetric synthesis is illustrated to be effective for stereochemical control in fragment assembly, a task often encountered in convergent natural product synthesis. The stereochemical outcome of aldol reactions involving three chiral components supports a rule of approximate multiplicativity of facial selectivities intrinsic to the chiral reactants involved in each reaction.     

Ring-opening polymerization of unsaturated alicyclic compounds

The ring-opening polymerizations of cyclooctene, cyclododecene, 1,5-cyclooctadiene, 1,5,9-cyclododecatriene, 3-methylcyclooctene, and 3-phenylcyclooctene have been carried out by using a two-component catalyst system composed of ethylaluminum dichloride and tungsten hexachloride. NMR and infrared analyses of the respective polymers indicate structures which are consistent with a ring-cleavage mode of propagation. No evidence for double-bond shifts or transannular reactions during the polymerizations of 1,5-cyclooctadiene, 1,5,9-cyclododecatriene, 3-methylcyclooctene, and 3-phenylcyclooctene was found. The polymerizability of substituted, unsaturated, mediumsized alicyclic monomers suggests a convenient method for synthesis of certain perfectly alternating terpolymers. Since polymerizations occurred rapidly with little evolution of heat, it was concluded that entropy is a substantial contributor to the free energy of the ring-opening polymerization of medium-sized, unsaturated alicyclic monomers.     

Sound attenuation in metals: Reformulation of Pippard theory to include microscopic band structure and scattering

Pippard's theory is written in Boltzmann equation form which allows both band effects and microscopic scattering to be included. A new formulation of deformation potential theory is an essential ingredient. Numerical calculations are given for Cu, using realistic electron and phonon eigenstates and the rigid-muffin-tin model for electron-phonon coupling. The calculations cover the crossover from hydrodynamic to quantum regimes, and show satisfactory agreement with experiment.     

The photoelectron spectra of gaseous alkali halides

The He I photoelectron spectra of the gaseous forms of CsF, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, NaI, KI, RbI, and CsI have been obtaine using a high-temperature spectrometer equipped with an internally-located, laser-beam heated sample oven. The spectral bands have been assigned molecul origins by use of MO calculations, spin—orbital splitting considerations, band intensity relations, polymer formation tendencies, and mass spectromet     

3-Aryl-5-[(aryloxy)methyl]-3-[(1H-1,2,4-triazol-1-yl)methyl]-2-methylisoxazolidine derivatives. Synthesis and antifungal activity

The synthesis and antifungal activity of a novel series of 3-aryl-5-[(aryloxy)methyl]-3-[(1H-1,2,4-triazol-1-yl)-methyl]-2-methylisoxazolidines are described. The in vitro activity was evaluated in solid agar cultures against a variety of dermatophytes and yeast fungi, while in vivo activity was measured in an immune-compromised mouse model of systemic candidiasis. The activity of the title series was compared to that of ketoconazole and one derivative, the cis-3-(4-chlorophenyl)-5-(4-chlorophenyloxy)methyl analogue 5f was found to possess a similar potency in the in vivo assay. Structure-activity relationship correlations are also discussed.     

Stereoselectivity in the electrophile-promoted cyclizations of a hydroxyolefin derived from arabinose. Synthesis of a phosphonate isostere of β-(=D)-arabinose-1, 5-diphosphate

Cyclization of droxyolefin 3, either with NBS or Hg(OAc)₂, gives predominantly the β isomer of a $\text{C}$-arabinofuranoside structure. Carbohydrate phosphonate 1 was synthesized from bromide 4a in six steps.     

Studies of the degradation of organotin stabilizers in poly(vinyl chloride) during gamma irradiation

Organotin stabilizers of the type Bu₂SnX₂ (X = SCH₂CO₂C₈H₁₇ or O₂CCH?CHCO₂C₈H₁₇) present in poly(vinyl chloride) (PVC) and subjected to varying doses of gamma irradiation in the range 1–200 kGy (0.1–20 Mrad) are shown to suffer degradation with dealkylation to form monobutyltin trichloride and tin(IV) chloride, which have been characterized by a subsequent alkylation procedure followed by gas chromatographic analysis. The extent of degradation of the stabilizers on prolonged gamma irradiation is much more severe than during thermal degradation leading to comparable blackening of the polymer.