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Chapter 1 Introduction to the enantioselective catalysis 1.1 General aspects: optical activity and chirality Any material that rotates the plane of polarized light is said to be optically active and molecule of this materials is nonsuperimposable on its mirror image (Fig. 1-1). If a molecule is superimposable on its mirror image, the compound does not rotate the plane of polarized light; it is optically inactive. The property of nonsuperimposability of an object on its mirror image is called chirality. If a molecule is not superimposable on its mirror image, it is chiral. Inverse logic is also true, i.e. if a molecule is superimposable on its mirror image, it is achiral. This is a necessary and sufficient requirement. Fig. 1-1. Superimposable (up) and nonsuperimposable (bottom) models of molecules. If a molecule is nonsuperimposable on its mirror image, the mirror image must be a different molecule, since superimposability is the same as identity. Both real molecule and its mirror image are called enantiomers. Enantiomers have identical (without considering interaction between elemental particles i.e. weak interaction [1]) physical and chemical properties except in two important respects: 1. They rotate the plane of polarized light in opposite direction, though in equal amounts. 2. They react at different rate with other chiral compounds. These rates may be so close together that the distinction is practically useless, or reaction rate of one enantiomer might be significantly far from another one. This is the reason that
many compounds are biologically active while their enantiomers are not active or lead to different reaction results. The mixture of enantiomers in equal amounts is called racemic mixture or racemate. The separation of a racemic mixture into its two enantiomers is called resolution. It is important to mention that the presence of optical activity always proves that a given compound is chiral, but its absence does not prove that the compound is achiral. A compound that is optically inactive may be achiral, or it may be a racemic mixture. Optically active compound may be classified into several categories. 1. Compound with a chiral carbon atom. If there is only one carbon atom with four different substitutes (so called chiral carbon atom), the molecule must be optically active. The optical activity has been detected even for compounds, where one group is hydrogen and another deuterium i.e. 1-butanol-1-d ( Fig 1-2) [2]. C 2 H 5 H C D Fig. 1-2. 1-butanol-1-d [3]. 2. Compound with other quadrivalent chiral atoms. A molecule containing an atom that has four bonds pointing to the corner of a tetrahedron will be optically active if the four groups are different. Among atoms in this category are Si [4], Ge [5], Sn [5] and N (in quaternary salts or N-oxides). 3. Compounds with tervalent chiral atoms. Atoms with pyramidal bonding might be expected to be optically active if the atom is connected to three different groups, since the unsaturated pair of electrons is analogous to a fourth group. For example, a secondary or tertiary amine (Fig. 1-3) where X, Y and Z are different. However due to the rapid oscillation of the lone pair from one side of the XYZ plane to the other and following conversion of the molecule into its enantiomers it is very difficult to isolate and even detect an enantiomer. The inversion is less rapid in substituted ammonias [6-8] and phosphates [9-12] and in suitable cases the inversion energetic barrier can be increased and such enantiomers could be detected and separated at room temperature [13, 14]. OH Z N X Y Fig. 1-3. Chiral amine [3]. 4. Suitably substituted adamantine. Adamantines bearing four different substitutes at the bridgehead positions are chiral and optically active and could be resolved [15]. This type of molecule (Fig. 1-4) is a kind of expanded tetrahedron and has the same symmetry properties as any other tetrahedron. CH 3 H COOH Br Fig. 1-4. Example of adamantane [3]. 2
Page 1 and 2: Preparation and Characterization of
Page 3 and 4: 5.4 Summary 66 Chapter 6 Cinchonidi
Page 5: Abstract Studies of the interaction
Page 9 and 10: Fig. 1-7. Hexahelicene [3]. 7. Chir
Page 11 and 12: R H COOH C OH CH 3 H COO - Bricine-
Page 13 and 14: Catalyst activity, expressed in the
Page 15 and 16: In fact, there are only two heterog
Page 17 and 18: similar way as relative abundance o
Page 19 and 20: surface concentration of cinchonidi
Page 21 and 22: site on Pt surface formed by a adso
Page 23 and 24: Chapter 2 Introduction to the nanos
Page 25 and 26: Triangular prism 5 4 Comments: A -
Page 27 and 28: precursors and building-up. This me
Page 29 and 30: 2.3 Preparation of nanoclusters on
Page 31 and 32: Paris Marseille Ljubljana Synphos Q
Page 33 and 34: Chapter 4 Cinchonidine modified Pt
Page 35 and 36: dihydrocinchonidine (355 mg or 1.2
Page 37 and 38: Table 4-1. Comparison between 5 % P
Page 39 and 40: widening can be used in estimation
Page 41 and 42: 1 Absorbance 0.1 2 1600 1400 1200 1
Page 43 and 44: the focus of these prior experiment
Page 45 and 46: Fig. 4-11. Tilted adsorbed cinchoni
Page 47 and 48: sci., QL. comp. 768 (str) 756 (str)
Page 49 and 50: Conversion, % 100 80 60 40 ITP time
Page 51 and 52: 6A c 10 19.5 B, 20 61 0 3 0.18 0.51
Page 53 and 54: pressure, exposing time, cinchonidi
Page 55 and 56: Fig. 4-16. Linear relationship betw
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1 , 1209 cm -1 and 1382 cm -1 remai
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Our results are in line with previo
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eaction. The stability of the catal
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Table 5-1. Ee and reaction rate ind
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Enantiomeric excess, % 85 80 75 A2
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35 30 Before After Percent of parti
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catalyst activation seems to indica
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Table 5-3. Assignment of some vibra
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6.2 Experimental Materials Cinchoni
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Fig. 6-3. TEM image of cinchonidine
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From the results of EP and EB hydro
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enhancement. However the exact fact
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Further, this family of man-made li
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Fig. 7-2. TEM of quiphos modified P
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of quiphos adsorbed on Pt and Pd an
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Fig. 7-8 Flat adsorbed quiphos via
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comp., H 11,12,13,14 2 C b., 2 P 11
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Chapter 8 “Quiphos-spider” modi
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flat crystal surface due to the hig
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Chapter 9 Diphos and diop modified
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Table 9-1. Average crystal size of
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Fig. 9-4. Conformation of diphos mo
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ings. Due to these reasons we can n
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Fig. 9-9. Proposed orientation of a
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The model of adsorption of diop on
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The calculation of energy of formin
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For the preparation of synphos modi
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1 2 20 40 60 80 2Θ Fig. 10-3. XRD
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The DRIFT spectra of synphos (Fig.
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peaks which can be used for analysi
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References [1] G.E. Tranter, J. Che
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[64] A. Szabo, N. Kunzle, T. Mallat
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[128] J.D. Aiken III, R.G. Finke, J
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[189] K. Umezawa, T. Ito, M. Asada,
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I declare that the current Ph.D. th
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