Guy J. Collin

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.

The Variations of Essential Oil Composition During the Extraction Process. The Case of Thuja occidentalis L. and Abies balsamea (L.) Mill

Abstract From analyses of various samples of essential oils extracted by hydrodistillation from the branches of Thuja occidentalis L. and Abies Balsamea (L.) Mill., it was shown that there are extensive variations in the concentrations of the main components. The content in thujones and fenchone reaches a maximum value of 80 % after 40–50 minutes for cedarleaf oil. After 60 minutes, the concentrations in α-pinene and β-pinene in balsam fir oil are maximum at 15% and 40%, respectively.

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.

Photolysis of n-butene and isobutene at 174.3 – 174.5 nm (7.10 eV)

Abstract The photolysis of n-butene and isobutene was carried out in a static system using nitrogen resonance lines at 174.3 – 174.5 nm (7.11 - 7.10 eV). The main fragmentation process of the photoexcited n-butene molecule is the CC split in the β position to the double bond. The primary quantum yield Φ is 0.66. The Φ value for the α CC split of isobutene is equal to 0.78. The stabilization and decomposition processes of (C3H5)* radicals formed in both systems are discussed. From the Stern—Volmer plots it is concluded that these radicals are formed in two distinct energy states. Contrary to our earlier report on cis-2-butene photolysis at the same wavelength, stabilization of the primary photoexcited butene molecules was observed. Certain results obtained at different photon energies are compared.

Essential Oils from Bolivia. III. Asteraceae: Artemisia copa Philippi

Abstract The chemical composition of the essential oil obtained from Artemisia copa growing in the high valley region of Bolivia, Province of Cochabamba, was determined by a combination of GC and GC/MS measurements. The main constituents were β-thujone (42%), chamazulene (6.5%) and a homoterpene (6.0%) as well as limonene (5%) and α-pinene (4.8%).

Composition of the essential oil of Ledum groenlandicum

Abstract The composition of the essential oil of Ledum groenlandicum Retzius was investigated. This oil was obtained by steam distillation (hydrodistillatio

Ring contraction of cyclic olefins: chemical processes specific to electronically excited states?

Abstract The photochemical ring cleavage and ring contraction reactions of cyclic olefins are reviewed. The retro Diels-Alder processes cannot be unambiguously linked to a particular electronic state. Although there seem to be some differences between the bicycloalkane products observed in the photosensitization (triplet) and the direct photolysis (singlet) of cyclo-olefins, these differences do not warrant assignment of the formation of a given bicycloalkane to a particular electronic state. Ring contraction to the corresponding vinylcycloalkane can occur from either the triplet or the “hot” ground state. The formation of methylenecycloalkanes appears to be a reaction specific to a Rydberg singlet state of the cycloalkenes.

On the choice of radical scavengers in the photolysis of cis-2-butene and 1-pentene at 147 nm

Abstract We have studied the effect of small quantities of O 2 , NO, NO 2 , SO 2 , HI, and H 2 S added as radical scavengers in the 8.4 eV (147 nm) photolysis of cis -2-butene and of 1-pentene- d 10 . Efficiency of methyl radical scavenging is in the decreasing order HI > NO 2 > NO > O 2 > H 2 S > SO 2 . NO 2 , SO 2 and H 2 S initiate the cis—trans isomerization of 2-butene. HI produces a deposit of iodine on the window; SO 2 and H 2 S produce a sulphur deposit decreasing in each case the transmission of the window. HI and cis -2-butene are in competition to scavenge hydrogen atoms: k (H + HI)/ k (H + cis -2-butene) = 21.2 ± 1.1. HI scavenges allyl radicals formed in the pentene photolysis; H 2 S does not. Finally we have observed fragmentation reactions of the photoexcited cis -butene and 1-pentene molecules which were not previously observed:

Aromas from Quebec. I. Composition of the essential oil of the rhizomes of Acorus calamus L.

Abstract The chemical composition of the essential oil obtained from the rhizomes of Acorus calamus (sweet flag) collected in the Grondines region, Province of Quebec, was determined by GC/FID and GC/MS analyses. Several components were isolated by liquid chromatography and were identified by various NMR experiments such as: 1H-NMR, 13C-NMR, HSQC, HMBC, and NOESY. The major compounds were identified as preisocalamenediol, acorenone, shyobunone, and cryptoacorone. The complete stereochemical structure of cryptoacorone was elucidated