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Building Aromaticity Scales

The above reactivity indices-based aromaticity scales are now computed within the presented quantum chemical schemes for a limited yet significant series of benzenoids containing the life atoms of Table 4.4 (see Table 4.5). The AIM of aromaticity scales are those of (Putz, 2010a)  [Pg.459]

TABLE 4.4 Main Geometric and Energetic Characteristics for Atoms Involved in Organic Compounds Considered in this Work (see Table 4.5), as Radii From Putz et al. (2003) and Polarizabilities (Pol) Based Upon Eq. (4.15b), Along the Electronegativity (X) and Chemical Hardness (ri) From Putz (2006,2008b), Respectively (Putz, 2010a) [Pg.460]

They are based exclusively on the data of Table 4.4 with the AIM results listed in Table 4.5, the 5th, 9th, and 10th coliunns, respectively the present discussion follows (Putz, 2010a). [Pg.460]

Within Semi-Empirical Quantum Chemical Methods All Energetic Values in Electron-Volts (eV) (Putz, 2010a) [Pg.465]

Compound CNDO INDO MIND03 MNDO AMI PM3 ZINDO/1 ZINDO/S [Pg.465]


From the results reported to date, it seems that the manner in which haptens are attached to carrier proteins leads to significant differences in certain cases. Clearly, haptens designed with aromatic moieties between the linkage to the immunogenic carrier protein and the TSA motif often have better antibody recognition. Recently, Hilvert pointed out that on both micro and macro levels, mechanistic improvements arise as a function of time. The differences in time scales for the evolution of natural enzymes and antibodies — millions of years versus weeks or months — also appear to be an explanation of the low efficiency of antibody catalysts. He also highlighted that the unique immunoglobulin fold has not been adopted by nature as one of the common scaffolds on which to build enzyme catalytic machinery. Therefore, antibody structure itself places limitations on the kind of reactions amenable to catalysis. [Pg.336]

The ADH from Lactobacillus brevis (Riebel, 1997) has a broad substrate specificity and converts even bulky aromatic ketones with high activity (Hummel, 1999 Wolberg, 2001). In addition, the enzyme is the best characterized completely (R)-specific ADH. The enzyme belongs to the class of short-chain dehydrogenases and its 3D structure has recently been solved (Niefind, 2003). The recombinant form of L. brevis ADH in E. coli accepts a variety of /j.d-dikelo esters as was determined in the synthesis of potential building blocks for HMG CoA reductase inhibitors (see also Chapter 13, Section 13.3.2) (Wolberg, 2001). tert-Butyl 3,5-dioxohexanoate and tert-butyl 3,5-dioxoheptanoate were reduced on a preparative scale to afford the corresponding (R)-<5-hydroxy-/3-keto esters with 99.4% e.e. and 98.1% e.e., respectively. [Pg.186]

Based on these biological data, two commercial forms of a-tocopherol (or their more stable acetate derivatives) are currently being produced by independent approaches [7, 8], Totally synthetic vitamin E, which is an equimolar mixture of all eight stereoisomers of a-tocopherol, is produced at a rate of over 25000 tons per year for the application in feed, food, and the pharma industry. The large-scale industrial synthesis of (all-rac)-a-tocopherol uses 2,3,5-trimethylhydroquinone (11) as the aromatic building block and the C2o compound isophytol (12). The acid-catalyzed condensation reaction in the last step delivers (all-rac)-3 (Fig. 2) [21-25],... [Pg.73]

The most simple method of obtaining a porphyrin on the gram scale is to reflux a dilute benzaldehyde-pyrrole mixture in propionic acid (141°C) for 30 minutes, cool, and filter. A 20% yield of crystalline porphyrin is easy to achieve (Scheme 6.3.1) (Lindsey et al., 1987, 1994 Prathapan et al., 1993). Even pentamers have been obtained by such a reaction in one step from a porphyrin benzaldehyde building block and pyrrole. One just has to carry out the primary formation of the porphyrinogen at a relatively low concentration (10 M) and under nonoxidative conditions, which allow the rearrangement of undesired polymers. Up to 50% of the colorless porphinogens are obtained by acid-catalyzed condensation of pyrrole and aromatic aldehydes under nitrogen. [Pg.283]

Vitamin E is the most important lipid-soluble antioxidant in biological systems. (all-rac)-a-Tocopherol (synthetic vitamin E, 1) is the economically most important product industrially prepared on a multi-10 OOOt/year scale and mainly used in animal nutrition [50]. In the large-scale syntheses of 1, 2,3>5-trimethylhydroquinone (6) is used as the aromatic key building block, which is condensed with isophytol (2) to yield 1 by all producers worldwide (Scheme 7.1). Trimethylhydroquinone (TMHQ, 6), in turn, is obtained from trimethylquinone (TMQ, 5) by reduction procedures, in particular catalytic hydrogenation. Besides other possibilities to access TMHQ (6), this route is generally preferred, and efficient oxidation processes for the production of quinone 5 from alkylated phenols are, therefore, of high interest [51]. [Pg.106]

Only for a coherent excitation (i.e., for AE F) can one expect time dependence of the emission spectrum. The vibrational redistribution corresponds here to the time evolution (coherence loss) of the initially prepared, nonstationary s> state (Trie, 1976 Mukamel, 1978). Initial, narrow-band s>-> 3 emission would decay and the broad-band l - g emission would build up at the time scale of fi/F. To our knowledge, such a behavior has never been evidenced in a convincing way. The reason for it may lie in the choice of molecular systems, which has so far been limited to aromatic molecules with no or small substituents. In such molecules, the coupling... [Pg.379]

An interesting process for the manufacture of p-cresol, which shows that the build-up of aromatics from low molecular components should always be considered as an alternative, is the Diels-Alder reaction of isoprene and vinyl acetate. This process, however, has not been exploited on an industrial scale. [Pg.168]


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