Hélène Deslauriers

Essential oils of Baccharis salicifolia, B. latifolia and B. dracunculifolia

Abstract Samples of the essential oil from Baccharis salicifolia, four samples from B. latifolia, and one sample from B. dracunculifolia collected in the high valleys of Bolivia in the province of Cochabamba were analysed by a combination of gas chromatography and mass spectrometry. The identified products may be divided into four different groups: monoterpenes, oxygenated monoterpenes, sesquiterpenes, and various oxygenated sesquiterpenes such as germacrone and ledol. The latter compounds are characteristic constituents of the essential oils of Ledum groenlanicum. Rather unusual monooxygenated compounds with a cadinane structure were also detected, including verboccidentafuran, chromoleanin and related compounds.

Essential Oil of Tansy (Tanacetum vulgare L.) of Canadian Origin

ABSTRACT The essential oils and microwave extracts obtained from 25 individual plants of tansy (Tanacetum vulgare L.) occurring in the Chicoutimi area (Quebec) were examined by a combination of GC and GC/MS. Several chemotypes were observed, two of them probably for the first time. Half of the plants belong to a camphor-1,8-cineole-borneol (concentration >52%) mixed chemotype. The β-thujone chemotype (>60%) was also present in six samples. Four specimens of a chrysanthenone type (>50%) were also observed. Finally, one sample showed a high concentration of dihydrocarvone (>60%). Following proper identification of individual plants by the microwave technique, the essential oils from three lots of plants were obtained and macroscopic properties were recorded. The optical rotation showed tremendous variations from one sample to another. A commercial sample produced in the vicinity of Quebec City belonged mainly to the β-thujone chemotype.

The vacuum UV photolysis of 1-hexene and 1-hexyne

Abstract A comparative study was made of the photolysis of 1-hexene and 1-hexyne at 184.9 and 147 nm. Three primary processes were observed in each system. They are, in decreasing order of importance, the rupture of the β(CC) bond, the rupture of the γ(CC) bond and the retro-ene process. Thus the behaviour of both photoexcited molecules is similar to a first approximation. However, there are meaningful differences. In particular, the rupture of the γ(CC) bond is relatively more important in the 1-hexyne case and leads to the formation of vinylacetylene at 147 nm. This observation suggests that the γ(CC) rupture may be the result of isomerization of the photoexcited molecule (a 1,3 hydrogen shift) which is followed by the rupture of the β(CC) bond.

Vacuum UV photolysis of n-1-hexene and 4-methyl-1-pentene

Abstract We studied the vacuum UV photolysis of n-1-hexene and 4-methyl-1-pentene at 147, 163 and 174 nm. In both systems the use of NO or O2 and DI indicates that the main fragmentation process (Φ ≈ 0.8) of the 147 nm photoexcited molecule is the breaking of the CC bond located at the β position. This process leads to the formation of allyl and propyl radicals. The propyl radicals decompose further at low pressure, giving rise to the formation of ethylene or propylene. By following the pressure effect on the ethylene or propylene quantum yields, and using RRKM results, it is shown that the n-propyl radicals formed in the n-1-hexene photolysis carry less energy than would be expected from a statistical distribution of the excess energy. The situation seems to be more complex for 4-methyl-1-pentene, and the isopropyl radicals have an energy content not far from the statistical distribution.

Volatile Constituents of the Essential Oil of Kaunea longipetolia (Sch. Bip. ex Rusby) K. & K.

ABSTRACT The essential oil of Kaunea longipetolia was analyzed by GC/MS. The oil was found to contain 66 constituents, of which 39 were identified. The identified products may be divided in three different groups: the monoterpenyl acetates (geranyl formate, 9%) and small amounts of monoterpenyl alcohols, the sesquiterpenes (β-caryophyllene, 9%), and the oxygenated sesquiterpenes (nerolidol, 24%).

Isomerization of unsaturated radicals. VI. Isomerization of 3-cyclopenlenyl and pentamethylene radicals

The 184.9 nm photochemistry 0f gaseous 3-methylcyclopentene and 3-methyl-1,4-pentadiene have been studied. Both photoexcited species decompose mainly through the primayy rupture of the C-CH3 bond. Vibrationally excited 3-cyclopenennyl and pentamethylene radicals are formed in the primayy decomposition in the former and latter systems respectively. These radicals are connected through isomerization reactions: in the presence of DI, the isomers cyclopenten,, and trans-1,3-pentadtene and/or vinylcyclopropane are formed in both systems. The quantum yields depend on the pressure and the starting monomer: cyclopentene and cyclopentadiene are the major products from the photolysis of 3-methylcyclopentene + DI mixtures and only minor quantities of the other C5H8 compounds are formed. Cyclopentadiene is the major product of the photolysis of 3-methyl-1,4-pentadiene + O2 mixtures whereas vinylcyclopropane and trans-1,3-pentadiene are the major C5 producss of the photolysis of 3-methyl-1,4-pentadiene + DI mixtures.The geometries of 3-cyclopentenyl and of the structures at the six critical points in the torsional potential energy curve (TPEC) for rotation about the 2- and 3-C-C bonds in the open chain pentamethylene species have been optimized completely by ab initio RHF-SCF gradient methods. For the open-chain structures the bond orders, bond lengths and the free valence (primarily associated with the central carbon atom) all correspond to 1,4-pentadien-3-yl conformations. In the ground state there is a high barrier to formation of 3-cyclopentenyl from 1,4-pentadien-3-yl. The features (relative energies and torsionll barriers) of the TPEC for 1,4-pentadien-3-yl explain the ESR observations for the open chain C5H7 radical rotamers.

High pressure photochemistry of alkenes. 6. the caee of 1-methylcyclopentene at 184.9 and 147.0 nm

The degradaiion of the 184.9 nm photoexcited 1-methyl-1-cyclopentene molecule shows the involvement of various excited isomers. The most important fragmentation products are 1- and 2-methyl-1,3-cyclopentadiene. These products are probably the result of a one-step elimination process of a hydrogen molecule. This process has also been observed in the case of the 184.9 nm photochemistry of cyclopenten. On the other hand, the involvement of isomers, although possible, is not so obvious at 147.0 nm. Moreover, in this case, the 1- and 2-methyl-1,3-cyclopentadiene formation is the result of hydrogen atom elimination in a two-step process. Cyclopentadiene, ethylene, and various C3 and C4 compounds are formed as well as methyl radicals and hydrogen atoms. These products are probably formed in successive elimination reactions as this is also observed in acyclic alkenes.

The vacuum and very far UV photolysis of 1-butyne: The effects of added molecular oxygen

Abstract The photolysis of 1-butyne has been studied between 147.0 and 213.8 nm. The propene quantum yields measured either in the pure system or in the presence of small amounts of oxygen or nitric oxide lead to the conclusion that the propene formation results from reactions between oxygen atoms and 1-butyne. However, at pressures higher than 200 Torr, the decrease in the propene quantum yields indicates a high efficiency for the stabilizing process of the involved intermediates. Moreover, the increase in the ethylene quantum yield on the addition of small amounts of oxygen supports the idea that triplet excited species are active in the 1-butyne system, although proof is needed either to corroborate or to show up the weakness of this assumption.

The 147 nm photolysis of either oxygen or nitrous oxide in the presence of 1,2-butadiene: Reactions of oxygen atoms

Abstract The addition of molecular oxygen to the 147 nm photolysis of gaseous 1,2-butadiene leads to a large increase in the propene quantum yield. We have shown that this propene formation is linked to the production of oxygen atoms through the direct photolysis of molecular oxygen. Moreover, from the study of mixtures of nitrous oxide and 1,2-butadiene, it can be seen that O( 3 P), O( 1 D) and O( 1 S) atoms react with butadiene in similar reactions, and that O( 1 D) and O( 1 S) have reaction rates similar to their collision rate:

Volatile constituents of the essential oil of Lepidophyllum quadrangulare (Meyen) Benth. and Hook

ABSTRACT The essential oil of Lepidophyllum quadrangulare was analyzed by a combination of GC/MS. The oil was found to contain 67 constituents of which 37 were identified. The major compounds were α-pinene (17–19%) and β-pinene (11–13%), and a variety of sesquiterpenes such as δ-cadinene (8–10%), γ2-cadinene (1.4–1.7%), γ-cadinene (0.6–0.7%) and α-muurolene (2.0–2.3%).