Search results for "kemialliset reaktiot"
showing 10 items of 20 documents
Asymmetric Synthesis of Dihydropyranones with Three Contiguous Stereocenters by an NHC‐Catalyzed Kinetic Resolution
2021
An oxidative NHC-catalyzed kinetic resolution (KR) of racemic mixtures is presented. The developed reaction furnishes tricyclic dihydropyranones with three contiguous stereocenters in excellent dia- and enantioselectivity, with good-to-moderate yields. Mechanistic studies indicate that the rate-determining step of the reaction is the formation of the Breslow intermediate, while the selectivity determining step occurs later in the mechanism. The presented methodology enables rapid synthesis of complex structures in a single step. peerReviewed
Experimental and computational studies of unconventional main group compounds : stable radicals and reactive intermediates
2017
Ever since their discovery, radicals have intrigued the minds of experimental and theoretical chemists alike. While the vast majority of radicals are transient species, a large number of stable and persistent radicals are also known. This has enabled the use of radicals in different applications. For example, radicals are highly useful in chemical synthesis due to their selectivity and functional group tolerance. Detailed knowledge of the electronic structure of synthetic intermediates, both radical and non-radical, enables chemists to improve existing synthesis routes and to design completely new ones. This thesis is divided into two parts. The first part begins with an introduction to the…
Computational investigations on rotational and vibrational spectroscopies of some diatomics in solid environment
2013
In this thesis, spectroscopic and structural properties of homogeneous para-hydrogen crystals and diatomic molecules embedded in rare gas crystals are explored by theoretical means. The agreement with experimental signatures indicates the suitability of the chosen quantum and classical methods to accurately describe the various low-temperature physical and chemical problems investigated at the laser laboratory. A novel explanation of band structures in Raman and IR spectra is given for CO in Ar. Rotational transition rules are found to dictate the spectral broadening of infrared and Raman band structures as a function of temperature. The results show that after photodissociation of matrix-i…
Biogenic Fenton process - A possible mechanism for the mineralization of organic carbon in fresh waters.
2020
To explore the mechanisms that mineralize poorly bioavailable natural organic carbon (OC), we measured the mineralization of OC in two lake waters over long-term experiments (up to 623 days) at different pH and iron (Fe) levels. Both the microbial and photochemical mineralization of OC was higher at pH acidified to 4 than at the ambient pH 5 or an elevated pH 6. During 244 days, microbes mineralized up to 60% of OC in the 10-mu m filtrates of lake water and more than 27% in the 1-mu m filtrates indicating that large-sized microbes/grazers enhance the mineralization of OC. A reactivity continuum model indicated that the acidification stimulated the microbial mineralization of OC especially i…
Detailed modeling of the kraft pulping chemistry : carbohydrate reactions
2020
The article introduces a detailed model for carbohydrate chemistry in kraft pulping. This article is continuation to the modeling work carried out for hot water extraction and chemical pulp bleaching. The model includes galactoglucomannan, xylan, and cellulose acid–base equilibria, in addition to peeling, stopping, and alkaline hydrolysis reactions of the same carbohydrates, as well as hexenuronic acid formation and degradation reactions. The Arrhenius parameters were applied from the literature or regressed against experimental data in the present study. The model is very successful in predicting the experimental data of carbohydrate reactions during kraft pulping. Many features of the pul…
Understanding selective reduction reactions with heterogeneous Pd and Pt : climbing out of the black box
2016
On potential of interactive multiobjective optimization in chemical process design
2006
Interaktiivinen monitavoiteoptimointi soveltuu hyvin teollisen kemian prosessisuunnitteluun. Jussi Hakanen esittelee väitöskirjassaan menetelmään pohjautuvan uuden työkalun, jollaista ei aiemmin ole ollut tarjolla. Hakanen on soveltanut työkalua onnistuneesti useiden kemiallisten prosessien suunnitteluun huomioimalla uudella tavalla enemmän kuin kaksi prosessin käyttäytymiseen vaikuttavaa tavoitetta.Aikaisemmin kemian prosessien suunnittelussa on otettu huomioon enintään kaksi prosessin toimintaan vaikuttavaa ristiriitaista tavoitetta. Hakasen esittelemä lähestymistapa ei rajoita huomioitavien tavoitteiden määrää, mikä mahdollistaa prosessien aiempaa realistisemman suunnittelun. Väitöstyöss…
Low‐Valent Germanylidene Anions: Efficient Single‐Site Nucleophiles for Activation of Small Molecules
2021
Abstract Rare mononuclear and helical chain low‐valent germanylidene anions supported by cyclic (alkyl)(amino)carbene and hypermetallyl ligands were synthesised by stepwise reduction from corresponding germylene precursors via stable and isolable germanium radicals. The electronic structures of the anions can be described with ylidene and ylidone resonance forms with the Ge−C π‐electrons capable of binding even weak electrophiles. The germanylidene anions reacted with CO2 to give μ‐CO2‐κC:κO complexes, a rare coordination mode for low‐valent germanium and inaccessible for the related neutral germylones. These results implicate low‐valent germanylidene anions as efficient single‐site nucleop…
Spectroscopic studies of semiconducting single-walled carbon nanotubes
2010
The unique nature of optical properties of single-walled carbon nanotubes (SWCNT), together with their promising potential applications, have created enormous interest towards the photophysics of SWCNT. Many aspects of carbon nanotubes originate from the electronic structure of carbon honeycomb lattice and one-dimensionality. SWCNTs exist in various chiral structures and diameters, which the optical and electrical properties are dependent on. It has been discovered that SWCNT excited states are excitonic with strong Coulomb interaction between the electron and the hole. However, many features of excitons are not yet well defined, such as absorption cross-sections, fluorescence quantum yield…
Transition path selection between ammonium nitrate solid phases IV, III and II
1994
Article dissertation. Contains an introduction and five articles. This study was made of factors affecting the transition paths between ammonium nitrate solid state phases IV, III and II. The effect of the sample preparation method was investigated by differential scanning calorimetry (DSC), transition mechanisms were explored with simultaneous DSC and Raman spectrometry developed for in situ investigation of the transitions, and the relationship between phase IV structure and the transition paths was studies by X-ray powder diffraction (XRD) and DSC. The results were analysed by partial least-squares regression (PLS) and principal component analysis (PCA). [Continues; please see the book]