Hal Wieser

Vibrational spectra and a valence force field for conformers of diethyl ether and deuterated analogues

Abstract From a comparison of the high-resolution infrared and Raman spectra of diethyl ether (I) and the deuterated analogues CD3CH2OCH2CD3 (II), CH3CD2OCD2CH3 (III), and CD3CD2OCD2CD3 (IV), fairly complete vibrational assignments for the trans-trans (TT) and trans-gauche (TG) conformers of all four species have been deduced, together with a valence force field adjusted to give a weighted least-squares fit to the observed frequencies of the TT conformer. From the temperature dependence of the infrared spectra bands were identified as belonging to either the TT or TG conformer (or to both). Information from Raman spectra and infrared vapour phase band contours was used to guide the computer refinement of the force field. An acceptable set of frequencies for the TG conformation of all four species has been calculated. In the vapour phase, the pure liquid, and in CCl4 and CS2 solutions the TT conformer predominates and is more stable than the TG conformer by about 1.1 kcal/mole. The greater stability of the TT conformer is interpreted in terms of a stabilizing interaction between the oxygen lone pair orbitals and the nearest hydrogen atoms of the methyl group, making the methyl group unsymmetrical and removing the degeneracy of the asymmetric CH3 stretching and CH3 bending vibrations.

Alternative Design for Improved FT-IR/VCD Capabilities

A Bomem MB100-based vibrational circular dichroism (VCD) spectrometer suitable for chiroptical studies in the infrared region is described. The optical layout utilizes the spectrometers external collimated beam. Standard VCD optics consisting of a KRS-5 polarizer and a ZnSe photoelastic modulator are mounted on an optical breadboard. A ZnSe meniscus lens focuses the beam on a small-area MCT detector. Several optical designs were examined to find the optimal positions of the optical elements. The experiments aimed to improve the energy throughput, minimize polarization artifacts, and increase signal-to-noise ratio to such an extent that single-enantiomer VCD spectra could be recorded routinely and dependably. Examples are presented illustrating the high-performance characteristics of the instrument.

Response of pocket gophers (Thomomys talpoides) to an operational application of synthetic semiochemicals of stoat (Mustela erminea).

This paper reports on laboratory bioassays and a large-scale field trial of synthetic mustelid anal-gland compounds in controlled-release devices designed for operational application to burrow systems of northern pocket gophers (Thomomys talpoides). The field study was conducted in an apple orchard in the Okanagan Valley of British Columbia. In laboratory bioassays, a 1∶1 mixture of 2-propylthietane and 3-propyl-1,2-dithiolane from the stoat (Mustela erminea) and 3,3-dimethyl-1,2-dithiolane from the ferret (M. putorius), dispensed in clay pellets (activated alumina), produced a significant avoidance response by gophers. All resident gophers were permanently removed from 4-ha control and treatment blocks prior to placement of stoat odor in burrows. As indexed by soil mounds, significantly fewer gophers colonized the treatment (40) than the control (68) removal area during a 5.5-month overwinter experiment. There was also a significant difference when comparing the number of mounds between pre-(79) and posttreatment (40) censuses. In addition, most gopher activity tended to occur on the perimeter of the treatment block. Abundance of gophers showed little difference between additional 4-ha control and treatment blocks where gophers had not been removed. The results of this study provide an alternative technique to toxicants for pocket gopher control on forest and agricultural land.

Comparison of release devices for stoat (Mustela ermined) semiochemicals used as montane vole (Microtus montanus) repellents

Fenced enclosures were used to simulate peak populations of montane voles (Microtus montanus) for field bioassays of a stoat (Mustela erminea) scent mixture in various controlled-release devices. A 1∶ 1 mixture of 2-propylthietane and 3-propyl-1,2-dithiolane was dispensed in capillary tubes, clay pellets (activated alumina), rubber septa, and plastic rope. Release devices were placed near, or attached to, young apple trees planted in blocks in two enclosures containing high populations of voles. The stoat scent mixture in rubber septa and plastic rope significantly reduced vole attack of trees compared with a control, pellets, and capillary tubes. In terms of complete girdling (tree mortality), this odor in septa and rope also significantly reduced feeding compared with the control, and the rubber septa formulation was more effective than either the pellets or capillary tubes. Fenced populations of voles may be used effectively to conduct field bioassays during low years in vole cycles. Variations of release devices (with this stoat scent mixture) based on rubber septa for broadcast application to depress vole population density and survival, and plastic rope attached to individual trees to generate an avoidance response, should be used for forest and agricultural crop protection.

Electronic and Vibrational Circular Dichroism of Model β-Lactams: 3-Methyl- and 4-Methylazetidin-2-one

The chiroptical properties of the simplest chiral β-lactams, 3- and 4-methylazetidin-2-one, 1 and 2, respectively, were investigated. The experimental vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectra were measured and compared with ab initio predictions. Both compounds were found to form dimers with calculated binding enthalpies and free energies of about −51 kJ/mol and −6 to −8 kJ/mol, respectively. The experimentally measured IR and VCD spectra were measured in concentrated nonpolar (CCl4) solution and are in agreement with the predicted IR and VCD spectra of the dimeric forms, 12 and 22, but not the monomers. The most intense dimer VCD bands originate from in-plane N-H wags, which perturb the H-bonded cyclic array. At the more dilute concentrations employed for the ECD spectra, the experimental ECD spectra in heptane were interpreted satisfactorily as arising from a mixture consisting predominantly of monomers. In protic solvent (H2O, MeOH), the ECD spectra are consistent with H-bonded monomers. Simple modeling suggests that the rotational strengths of the first electronic transition gain most of their intensity from the nonplanarity of the amide chromophore, the contributions of which follow a spiral rule previously enunciated.

The absolute configuration of 6,8-dioxabicyclo[3.2.1]octane and several methyl substituted derivatives

Abstract The enantiomers of 6,8-dioxabicyclo[3.2.1]octane and the alkyl substituted derivatives, exo- and endo-7-methyl, exo- and endo-5,7-dimethyl, 7,7-dimethyl, and exo- and endo-7-ethyl-5-methyl (exo- and endo-brevicomin), were synthesized stereoselectively with known configuration by standard synthetic methods, or with bakers yeast, or both. The correlation between the absolute configuration of the bicyclic rings and the optical rotation was established by means of chiral complexation gas chromatography for two molecules for which this correlation was not known previously. In all cases, the (1R) enantiomer exhibits positive rotation. The absolute configurations were established for the yeast products which were always produced in high optical purity.

The structure of bicyclo[2.2.1]heptanes: Norbornane, nornornene, norbornadiene, 7-oxanorbornane, and 7-thianorbornane

Abstract The structures of norbornane, norbornene, norbornadiene, 7-oxanorbornane, and 7-thianorbornane were completely determined by analytical gradient techniques in conjunction with ab initio Hartree—Fock molecular orbital theory. Geometric details obtained at the minimal STO-3G and split valence 3–21G levels of theory, are compared with data available from various experimental studies using both microwave and electron diffraction spectroscopy. Variations in the geometric parameters which ensue from introduction of the functional groups into the bicyclo [2.2.1] heptane skeleton are discussed in terms of perturbative molecular orbital (PMO) theory.

Influence of the plant antifeedant, pinosylvin, on suppression of feeding by snowshoe hares

This study investigated the influence of the plant antifeedants, pinosylvin and pinosylvin methyl ether (PME), on suppression of feeding by snowshoe hares (Lepus americanus). Screening bioassays showed clearly that pinosylvin suppressed feeding by hares when sprayed directly on coniferous tree seedlings. Pinosylvin odor, when associated with food (but not mixed with it), also significantly reduced consumption of rabbit chow by hares. Large pen bioassays indicated that both pinosylvin and PME significantly reduced feeding on tree seedlings by hares when the antifeedants were sprayed directly on trees. In field bioassays near Prince George, British Columbia, Canada, pinosylvin sprayed on trees and encapsulated in controlled-release devices of PVC plastic, with an internal wire as a twist-tie for attachment to tree, significantly reduced feeding by hares. Thus, pinosylvin will generate an “avoidance response” in terms of feeding by snowshoe hares. This response is likely triggered by an olfactory pathway based on positive results with controlledrelease devices attached to seedlings. Our study reports the first practical utilization of plant antifeedants for forest crop protection and wildlife management.

Vibrational assignments for trimethylene oxide and several deuterated analogues

Abstract Complete vibrational assignments below about 1400 cm−1 are presented for trimethylene oxide and its deuterated derivatives β-d2, α, α′-d4, d6, and α-d2, on the basis of the i.r. vapour phase spectra and the spectra of the solids at 15 K as thin films and in argon matrices, and the Raman spectra of the vapours and liquids. Previously reported assignments for the CH stretching, CH2 scissoring, and the ring puckering vibrations, as well as preliminary assignments for the CD stretching modes, are included for comparison.

Infrared and Raman spectra of diethyl ether complexes of MgBr2 and MgI2

Abstract Infrared (250–4000 cm −1 ) and Raman (100–4000 cm −1 ) spectra of diethyl ether solutions of MgBr 2 and MgI 2 and of the corresponding solid dietherate of MgI 2 are presented. Fairly complete vibrational assignments have been deduced for the etherate complexes. The spectra can be understood generally in terms of a conformational change in the complexed ether in favour of a greater population of ligands with gauche ethyl groups, relative to the distribution of conformers in free diethyl ether.