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- Bäcktorp, Carina, 1964, et al.
(author)
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A DFT comparison of the neutral and cationic Heck pathways.
- 2011
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In: Dalton transactions (Cambridge, England : 2003). - : Royal Society of Chemistry (RSC). - 1477-9234 .- 1477-9226. ; 40, s. 11308-11314
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Journal article (peer-reviewed)abstract
- The two distinct mechanistic pathways of the Heck reaction, cationic and neutral, are characterized computationally using DFT calculations with corrections for solvation and dispersion. The selectivity in each type of reaction is discussed in terms of the detailed reaction paths, and the two types are compared to each other. The geometries and energies of the selectivity-determining transitions states are analyzed in detail.
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| 5. |
- Bäcktorp, Carina, 1964, et al.
(author)
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Direct dynamics study of ultrafast vibrational energy relaxation in ice Ih.
- 2005
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In: The journal of physical chemistry. A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 109:14, s. 3105-10
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Journal article (peer-reviewed)abstract
- Car-Parrinello molecular dynamics (CPMD) and a previously developed wave packet model are used to study ultrafast relaxation in water clusters. Water clusters of 15 water molecules are used to represent ice Ih. The relaxation is studied by exciting a symmetric or an asymmetric stretch mode of the central water molecule. The CPMD results suggest that relaxation occurs within 100 fs. This is in agreement with experimental work by Woutersen and Bakker and the earlier wave packet calculations. The CPMD results further indicate that the excitation energy is transferred both intramolecularly and intermolecularly on roughly the same time scale. The intramolecular energy transfer occurs predominantly between the symmetric and asymmetric modes while the bend mode is largely left unexcited on the short time scale studied here.
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| 6. |
- Bäcktorp, Carina, 1964, et al.
(author)
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Mechanism of Air Oxidation of the Fragrance Terpene Geraniol
- 2008
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In: J.Chem.Theory Comput.. - : American Chemical Society (ACS). ; 4, s. 101-106
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Journal article (peer-reviewed)abstract
- The fragrance terpene geraniol autoxidizes upon air exposure and forms a mixture of oxidation products, some of which are skin sensitizers. Reactions of geraniol with O2 have been studied with DFT (B3LYP) and the computational results compared to experimentally observed product ratios. The oxidation is initiated by hydrogen abstraction, forming an allylic radical which combines with an O2 molecule to yield an intermediate peroxyl radical. In the subsequent step, geraniol differs from previously studied cases, in which the radical chain reaction is propagated through intermolecular hydrogen abstraction. The hydroxy-substituted allylic peroxyl radical prefers an intramolecular rearrangement, producing observable aldehydes and the hydroperoxyl radical, which in turn can propagate the radical reaction. Secondary oxidation products like epoxides and formates were also considered, and plausible reaction pathways for formation are proposed.
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| 7. |
- Bäcktorp, Carina, 1964, et al.
(author)
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Mechanisms of Air Oxidation of Ethoxylated Surfactants - Computational Estimations of Energies and Reaction Behaviors
- 2008
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In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 14:31, s. 9549-9554
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Journal article (peer-reviewed)abstract
- Pathways for formation of previously observed autoxidation products of ethoxylated surfactants have been studied by DFT (B3LYP). In addition to the established radical-chain reaction, several mechanistic possibilities for intramolecular fragmentation of the intermediate radicals have been characterized concerning reaction barriers and energies of transition states. The results can rationalize the formation of previously observed autoxidation products, including several, which have been implicated as strongly allergenic.
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| 8. |
- Bäcktorp, Carina, 1964, et al.
(author)
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Theoretical investigation of linalool oxidation.
- 2006
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In: The journal of physical chemistry. A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 110:44, s. 12204-12
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Journal article (peer-reviewed)abstract
- This study concerns the autoxidation of one of the most used fragrances in daily life, linalool (3,7-dimethyl-1,6-octadien-3-ol). It reacts with O2 to form hydroperoxides, which are known to be important contact allergens. Pathways for hydroperoxide formation are investigated by means of quantum mechanical electronic structure calculations. Optimized molecular geometries and harmonic vibrational frequencies are determined using density functional theory (DFT). Insight into how the addition of O2 to linalool occurs is obtained by establishing a theoretical framework and systematically investigating three smaller systems: propene, 2-methyl-2-butene, and 2-methyl-2-pentene. 2-Methyl-2-pentene was chosen as a model system and used to compare with linalool. This theoretical study characterizes the linalool-O2 biradical intermediate state, which constitutes a branching point for the further oxidation reactions pathways. Thus, the observed linalool oxidation product spectrum is discussed in terms of a direct reaction path, the ene-type mechanism, and the radical mechanism. The major hydroperoxide found in experiments is 7-hydroperoxy-3,7-dimethyl-octa-1,5-diene-3-ol, and the calculated results support this finding.
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| 9. |
- Bäcktorp, Carina, 1964, et al.
(author)
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Trans effects in the Heck reaction—A model study
- 2010
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In: Journal of Molecular Catalysis A: Chemical. - : Elsevier BV. - 1381-1169. ; 328:1-2, s. 108-113
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Journal article (peer-reviewed)abstract
- The selectivity-determining step in Heck arylation of styrene, the migratory insertion, has been modeled by DFT. In particular, the regio-selectivity has been studied as a function of the trans effect of several sets of small model ligands with different σ-donor and π-accepting abilities. It has been shown, both by analyzing the geometries and comparing the activation energies, that the TS for branched product formation is more sensitive than the TS leading to linear product, although most ligand combinations give a preference for the linear product. The branched TS is strongly destabilized by any strong ligand in a position trans to the alkene in the pre-insertion intermediate. For the ligand trans to the migrating group, a strong trans effect accelerates the reaction, more for the branched than for the linear product formation. On electronic grounds, the regio-selectivity and rate can be adjusted by considering not only the trans effect of a ligand, but also by controlling the position they will have in the migratory insertion step. Very importantly, the trans effect change in the selectivity-determining TS will be expected to give rise to Halpern-type selectivity, with the consequence that product distributions cannot be reliably predicted from observable intermediates.
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| 10. |
- Hagvall, Lina, 1978, et al.
(author)
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Fragrance compound geraniol forms contact allergens on air exposure. Identification and quantification of oxidation products and effect on skin sensitization
- 2007
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In: Chemical Research in Toxicology. - : American Chemical Society (ACS). - 0893-228X .- 1520-5010. ; 20:5, s. 807-814
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Journal article (peer-reviewed)abstract
- Fragrances are common causes of contact allergy. Geraniol (trans-3,7-dimethyl-2,6-octadiene-1-ol) is an important fragrance terpene. It is considered a weak contact allergen and is used for fragrance allergy screening among consecutive dermatitis patients. Analogous to other monoterpenes studied, such as limonene and linalool, geraniol has the potential to autoxidize on air exposure and form highly allergenic compounds. The aim of the present study was to investigate and propose a mechanism for the autoxidation of geraniol at room temperature. To investigate whether allergenic compounds are formed, the sensitizing potency of geraniol itself, air-exposed geraniol, and its oxidation products was determined using the local lymph node assay in mice. The results obtained show that the allylic alcohol geraniol follows an oxidation pattern different from those of linalool and limonene, which autoxidize forming hydroperoxides as the only primary oxidation products. The autoxidation of geraniol follows two paths, originating from allylic hydrogen abstraction near the two double bonds. From geraniol, hydrogen peroxide is primarily formed together with aldehydes geranial and neral from a hydroxyhydroperoxide. In addition, small amounts of a hydroperoxide are formed, analogous to the formation of the major linalool hydroperoxide. The autoxidation of geraniol greatly influenced the sensitizing effect of geraniol. The oxidized samples had moderate sensitizing capacity, quite different from that of pure geraniol. The hydroperoxide formed is believed to be the major contributor to allergenic activity, together with the aldehydes geranial and neral. On the basis of the present study and previous experience, we recommend that the possibility of autoxidation and the subsequent formation of contact allergenic oxidation products are considered in risk assessments performed on fragrance terpenes.
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