Toxicokinetics of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) in the European corn borer,Ostrinia nubilalis (Hübner)

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), the major hydroxamic acid present in corn, and its tritiated derivative, were prepared synthetically for use in the determination of the toxicokinetics of this insect deterrent in the European corn borer (ECB),Ostrinia nubilalis. In growth studies with DIMBOA (0, 0.05, 0.2, and 0.5 mg/g diet), the mean time to pupation and adult emergence were significantly lengthened by an increase in concentration. Pupal and adult weights, for both female and male, decreased with an increase in concentration. Increased larval and pupal mortality occurred at the highest concentration of DIMBOA. DIMBOA, at concentrations of 0.2 and 0.5 mg/g diet, resulted in a decrease in the number of egg masses produced per female, and at 0.5 mg/g diet, in a decrease in the number of eggs per egg mass. Larvae fed from the neonate stage on a diet containing 0.2 mg [(3)H]- + [(1)H]DIMBOA/g diet showed an increase in the content of label from fourth to fifth instar, but levels declined at pupation and emergence. A large amount of the labeled compounds was excreted by the insect in the pupal case. In dose-related studies, both uptake and excretion increased with an increase in concentration of DIMBOA (0.05, 0.2, 0.4 mg/g diet), while a body burden (concentration in the tissues/concentration in the frass) of approximately 0.25 was maintained for all concentrations. At the highest dose of DIMBOA (0.4 mg/g), the ECB increased consumption, possibly to compensate for the toxic effects of the compound. In topical application studies, elimination of the labeled compound in the frass was rapid, reaching 65% by 4 hr and 88% by 48 hr. Accumulation of label in tissues other than hemolymph was low. The results show that the ECB does possess adaptive mechanisms to deal with the effects of this host-derived compound.

UV photoelectron spectroscopic and computational study of 7-substituted cycloheptatrienes

The He(I) photoelectron (PE) spectra of cycloheptatriene (1), 7-methylcycloheptatriene (2), 7-methoxycycloheptatriene (3), 7-methylthiocycloheptatriene (4), and 7-diemthylaminocycloheptatriene (5) were recorded and interpreted using MO energies and ionization potentials acquired from B3PW91 calculations. Partial simulated PE spectra were in good agreement with the experimental results. The axial and equatorial conformers have distinct PE spectra as illustrated by simulation. The PE spectra of 2, 3, and 5 are representative of the equatorial conformers, while the PE spectrum of 4 was in accord with a 1:1 mixture of equatorial and axial conformational isomers based on spectral simulation. The calculated free energy differences between the equatorial and axial conformers are in the order of 2 kcal mol–1 (1 cal = 4.184 J) for compounds 2, 3, and 5, where the equatorial conformational isomer is lowest in energy. In the case of 4, the equatorial conformer was only marginally lower in energy than its axial counterpart, where the free energy difference is 0.1 kcal mol–1.Key words: 7-substituted cycloheptatrienes, He(I) photoelectron spectroscopy, B3PW91, spectral simulation.

Pyrolysis of 2-methoxy-5,5-dimethyl-2-methylthio- 2,5-dihydro[1,3,4]oxadiazole studied with photoelectron spectroscopy and DFT calculations — He(I) photoelectron spectrum of methoxy(methylthio)carbene

Gas-phase pyrolysis of 2-methoxy-2-methylsulfanyl-5,5-dimethyl-2,5-dihydro[1,3,4]oxadiazole (1) (also known as 2-methoxy-5,5-dimethyl-2-methylthio-2,5-dihydro[1,3,4]oxadiazole and 2-methoxy-2-methylthio-5,5-dimethyl-Δ3-l,3,4-oxadiazoline) in the source of an UV photoelectron spectrometer, by means of a CW CO2 laser as directed heat source, gave a photoelectron (PE) spectrum that included ionization bands belonging to acetone and methoxy(methylthio)carbene (3). Photoelectron spectra of authentic samples of (E)-1,2-dimethoxy-1,2-dimethyl thioethene (4), (Z)-1,2-dimethoxy-1,2-dimethylthioethene (5), S-methyl thioethanoate (6), and O-methyl ethanethioate (7), which can be derived by dimerization and rearrangement of the carbene, established that these compounds are not present in the pyrolysate. DFT calculations at the B3PW91/6-31+G(d,p) level and simulation of PE spectra at the B3LYP/6-31+G(d,p) level were instrumental in the interpretation of the experimental results. From the available experimental and calculated data, 3 is formed in a Sickle conformation upon pyrolysis of 1. Transition states for the rearrangement of 3 were examined with QTAIM. Key words: 2-methoxy-5,5-dimethyl-2-methylthio-2,5-dihydro[1,3,4]oxadiazole, pyrolysis, He(I) photoelectron spectroscopy, methoxy(methylthio)carbene, DFT calculations, QTAIM.

Bicyclo[3.2.0]hepta-1,3,6-triene — UV photoelectron spectroscopic and computational studies

Pyrolysis of N,N-dimethylbicyclo[3.2.0]hepta-3,6-dien-1-amine oxide (5) at 120 °C in the source chamber of the UV photoelectron (PE) spectrometer yielded bicyclo[3.2.0]hepta-1,3,6-triene (6). The triene dimerizes to yield a mixture of two dimers in equal amounts. A PE spectrum of an authentic mixture of dimers was also recorded for the purpose of spectral subtraction. Pyrolysis of 5 also generates dimethylhydroxylamine (7), a spectrum of which was also recorded from an authentic sample. Spectral subtraction allowed the first two ionization potentials of triene 6 at 7.2 and 9.8 eV to be identified. The resultant PE spectrum was compared very favorably with a simulated spectrum obtained from DFT calculations. A QTAIM analysis and calculation of delocalization indexes showed that while homoconjugation between C4 and C6 is negligible there is a weak through-space interaction between the bridgehead carbon atom C1 and C6 of the four-membered ring.Key words: bicyclo[3.2.0]hepta-1,3,6-triene, UV photoelectron spectroscopy, DFT calculations, QTAIM, delocalization indexes.

A calculational and ultraviolet photoelectron spectroscopic study of distorted amides

Distorted amides 3,4-dihydro-2-oxo-1,4-ethanoquinoline (1a), 3,4-dihydro-2-oxo-1,4-propanoquinoline (1b), 3,3,4,5-tetrahydro-2-oxo-1,5-ethanobenzazepine (1c), and 3,3,4,5-tetrahydro-2-oxo-1,5-propanobenzazepine (1d) and the model compounds 2,N-dimethyl-acetanilide (2a), 2,N,N-trimethylaniline (3), and benzoquinuclidine (4) have been studied calculationally and with He(I) ultraviolet photoelectron spectroscopy. We find good agreement between experimentally obtained ionization energies for 1b, 1c, 1d, 2a, 3, and 4 and values calculated with HAM/3 using the equilibrium geometries obtained at the HF/6-31G** level of theory. An excellent correlation between experimental ionization energies and orbital energies from Becke3LYP/6-31+G* calculations led to the characterization of the highest occupied molecular orbitals for these compounds and for 1a, whose photoelectron spectrum could not be obtained due to its reactivity in the solid state.Key words: distorted amides, He(I) photoelectron spectroscopy, Becke3LYP, molecular orbitals.

Thermolysis of 2,2-dimethoxy-5,5-dimethyl- Δ3- 1,3,4- oxadiazoline studied with photoelectron spectroscopy. He(I) photoelectron spectrum of dimethoxycarbene

Gas phase thermolysis of 2,2-dimethoxy-5,5-dimethyl- Δ3-1,3,4-oxadiazoline (1) in an ultraviolet photoelectron spectrometer by means of a CW CO2 laser as directed heat source at 26 W gave a complex PE spectrum that included ionization bands belonging to acetone, tetramethoxyethylene (3), and dimethyl oxalate (4). Subtraction of the spectra of acetone, 3, and 4 from the pyrolysis spectrum of 1 left a simple PE spectrum that is attributed to dimethoxycarbene (2) along with some ethane. ecke3LYP/6-31+G* calculations gave first adiabatic and vertical ionization potentials of 2 as well as orbital energies that are in perfect agreement with experimental values. From the available experimental and calculational data, 2 is assumed to adopt a w conformation.Key words: dimethoxycarbene, 2,2-dimethoxy- Δ3-1,3,4-oxadiazoline, tetramethoxyethylene, He(I) photoelectron spectroscopy, thermolysis.

Free-Radical Chemistry of Imines

Aryl radicals bearing an aldimino functional group as part of an ortho substituent cyclized by addition to C and/or N of the imino group. When the choice was between 5-exo closure to C and 6-endo closure to N, the former predominated. However, 6-endo closure to C predominated over 5-exo cyclization to N in isomeric imines. Absolute values of cyclization rate constants were determined and an explanation for the unusual 6-endo preference is offered. Chiral induction in 6-endo cyclization to C of an aldimine from D-glyceraldehyde acetonide was observed, and its sense was determined.

Synthesis of bicyclic diones and thiones. Facile methylation of the enolates of bicyclo[2.2.1]heptane-2,5-dione and bicyclo[2.2.2]octane-2,5-dione. An AM1 computational study of bicyclic enolates

A group of bicyclic ketones and thiones have been synthesized for homenolization studies. Bicyclo[2.2.1]heptane-2,5-dione (6) undergoes unusually rapid tetramethylation giving 3,3,6,6-tetramethylbicyclo[2.2.1]heptane-2,5-dione (1) in good yield. Treatment of 1 with P2S5 in xylene gave 3,3,6,6-tetramethylbicyclo[2.2.1]heptane-2,5-dithione (2) and 3,3,6,6-tetramethyl 15-oxo-bicyclo[2.2.1]heptane-2-thione (3), which was converted into 4 with Raney nickel. Bicyclo[2,2,2]octane-2,5-dione (7), prepared via a Diels–Alder reaction between 2-trimethylsilyloxy-1,3-cyclohexadiene and and α-acetoxyacrylonitrile followed by a one-step desilylation/hydrolysis, also undergoes facile tetramethylation giving 3,3,6,6-tetramethylbicyclo[2.2.2]octane-2,5-dione (5) in good yield. AM1 calculations were carried out on the α-enolates of bicyclo[2.2.1]heptan-2-one, 6, 5-methylidenebicyclo[2.2.1]heptan-2-one, and 4-acetylbicyclo[2.2.1]-heptan-2-one in an attempt to gain information on the source of the enhanced acidity of the C-3 hydrogens of 6 and 7. Keywords: bicyclic ketones, thiones, synthesis.

Conformational analysis and structure elucidation of 2,3-dimethyl- and 2,4-dimethyl-2,4-hexadienes by AM1 and He(I) ultraviolet photoelectron spectroscopy

A study of (E)-2,3-dimethyl-2,4-hexadiene (E-3) and (Z)-2,3-dimethyl-2,4-hexadiene (Z-3) by the semiempirical computational method AM1 and He(I) ultraviolet photoelectron spectroscopy (UPS) has established that this combination of AM1/UPS will be generally useful for detailing conformational and electronic properties of alkyl-substituted 1,3-dienes. This method was used to elucidate the structures of the stereoisomeric 2,4-dimefhyl-2,4-hexadienes obtained from the photolysis of 1,3,3,4-tetramethylcyclobutene (2). Keywords: 2,3- and 2,4-dimethyl-2,4-hexadienes, conformational analysis, AM1, He(I) photoelectron spectroscopy.

Studies of electronic excited states of substituted norbornenes by UV absorption, electron energy loss, and HeI photoelectron spectroscopy

Valence and inner-shell (C1s) electronic excitation spectra of norbornene, 2-methylnorbornene, and 2-trifluoromethylnorbornene have been measured by electron energy loss spectroscopy. These data have been complemented with gas- and solution-phase UV absorption spectra in the 5–6.7 eV range, HeI UV photoelectron spectra, and AM1 semi-empirical calculations for the three compounds. The valence shell energy loss and UV absorption spectra show marked variations throughout the series of compounds, suggesting the presence of at least three low-lying electronic excited states. The spectral bands have been assigned as due to π,R(3s), π,π*, and π, R(3p) excitations on the basis of their term values and the differences between their intensities in the solution and gas phase absorption spectra. The valence shell spectra indicate that while the vertically-excited π,R(3s) state is substantially lower in energy than the (vertically-excited) π,π* state in norbornene and the 2-methyl derivative, they are nearly isoenergetic in 2-trifluoromethylnorbornene. This difference in excited state manifolds is reflected in profound differences between the solution phase photochemistry of norbornene and the 2-trifluoromethyl derivative.The carbon 1s spectra are even more sensitive to substituent than the valence shell energy loss spectra. An interpretation is proposed which reflects the spatially localized character of inner-shell excitation and a "group orbitals" picture of the unoccupied MO's as accessed by C1s excitation. Keywords: Rydberg, electron energy loss, UV absorption, UV photoelectron spectroscopy, alkene, gas-phase.

Thermolysis of N-alkylated ethylenediamines: an ultraviolet photoelectron spectroscopy study

Thermolyses of N,N,N′,N′-tetramethylethylenediamine (1a), N,N,N′,N′-tetraethylethylenediamine (1b) and sym-N,N′-dimethylethylenediamine (1c) at 760–825 °C have been studied by ultraviolet photoelectron spectroscopy. Although the corresponding N-alkylated aminomethylene radicals were not observed, this study establishes that thermolysis of 1a is an efficient route to N-methylenimine (3a); methane, ethane, and ethene are the other major products. Diamine 1b yields, besides ethane, ethene, and propane, heretofore unreported N-ethylmethylenimine (3b). Diamine 1c yields imine 3a and methylenimine (3c), as well as hydrogen, methane, ethane, and ethene. Molecular orbital eigenvalues of the imines are calculated using HAM/3, MNDO, HF/STO-3G, HF/3-21G, and HF/6-31G* methods.

Reaction of diphenylcarbene with oxygen: a laser flash photolysis study

Diphenylcarbene reacts with oxygen with a rate constant of 5 × 109 M−1 s−1 in acetonitrile at 300 K. The reaction leads to an intermediate which absorbs strongly at ~410 nm, believed to be the carbonyl oxide, Ph2COO.

13C Chemical Shifts of Highly Substituted Bicyclo[2.2.1]heptanes

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13C Chemical Shifts of Highly Substituted Bicyclo[2.2.1]heptanes

The 13C chemical shifts have been determined for a series of highly substituted norbornanes. A comparison of the observed values with the expected chemical shifts, determined as described by Lippmaa, establishes that 13C shifts may be predicted reasonably accurately even in highly substituted norbornyl systems. Since substituted norbornanes definitely exist in synchro or contra twist forms as shown by Altona, the results show that Lippmaa's substituted shift parameters must already account for the major part of the increments that arise via hybridization changes resulting from the distortion of the [2.2.1]-skeleton.

The Preparation and Acetolyses of 5-Deuteriated exo-2-Norbornyl-p-bromobenzenesulfonates

The deuterionorborneols 2a, b, c, and e have been prepared and converted to the brosylates 1a, b, c, and e. The deuterium isotope effects determined spectrophotometrically for solvolysis in HOAc–KOAc are 1.00 ± 0.01, 1.01 ± 0.01, 0.99 ± 0.01, and 1.11 ± 0.01, respectively. These data establish that: (a) a steric deuterium isotope effect does not operate at C-5 and therefore probably not at C-6; (b) hyperconjugative stabilization of the norbornonium ion to the C-5 hydrogens is confirmed to be not important, and (c) provides the first experimental evidence that the hydrogen (deuterium) shift – internal return pathway contribution to the γ-deuterium isotope effects observed for 1d and e is minor.

Addition of ICl to Norbornene. The Preparation and Photochemical Isomerization of syn-7-Iodonorbornene

The addition of ICl to norbornene in the presence of pyridine yields nortricyclyl iodide (1c), endo-2-chloro-exo-3-iodonorbornane (2c), and syn-7-iodo-exo-2-chloronorbornane (3b) as the major products. Base-catalyzed elimination of HCl from 3b yields syn-7-iodonorbornene (6a) which is isomerized photochemically to anti-7-iodonorbornene (6b).