Previously unknown

A variety of methods have been developed by mathematicians and computer scientists to address this task, which has become known as data mining (see Chapter 9, Section 9.8). Fayyad defined and described the term data mining as the nontrivial extraction of impHcit, previously unknown and potentially useful information from data, or the search for relationships and global patterns that exist in databases [16]. In order to extract information from huge quantities of data and to gain knowledge from this information, the analysis and exploration have to be performed by automatic or semi-automatic methods. Methods applicable for data analysis are presented in Chapter 9. 

The use of penodic acid oxidation m structure determination can be illustrated by a case m which a previously unknown methyl glycoside was obtained by the reaction of D arabmose with methanol and hydrogen chlonde The size of the nng was identified as five membered because only one mole of penodic acid was consumed per mole of glycoside and no formic acid was produced Were fhe nng six membered fwo moles of penodic acid would be required per mole of glycoside and one mole of formic acid would be produced... 

Shock-wave compression is also used to study solid-solid phase transformation. Bancroft et al. [58] report a previously unknown phase transformation... 

The reactivities of the substrate and the nucleophilic reagent change vyhen fluorine atoms are introduced into their structures This perturbation becomes more impor tant when the number of atoms of this element increases A striking example is the reactivity of alkyl halides S l and mechanisms operate when few fluorine atoms are incorporated in the aliphatic chain, but perfluoroalkyl halides are usually resistant to these classical processes However, formal substitution at carbon can arise from other mecharasms For example nucleophilic attack at chlorine, bromine, or iodine (halogenophilic reaction, occurring either by a direct electron-pair transfer or by two successive one-electron transfers) gives carbanions These intermediates can then decompose to carbenes or olefins, which react further (see equations 15 and 47) Single-electron transfer (SET) from the nucleophile to the halide can produce intermediate radicals that react by an SrnI process (see equation 57) When these chain mechanisms can occur, they allow reactions that were previously unknown Perfluoroalkylation, which used to be very rare, can now be accomplished by new methods (see for example equations 48-56, 65-70, 79, 107-108, 110, 113-135, 138-141, and 145-146)... 

A simple preparative route to the previously unknown lH-3-pyrazolines via azomethine imines was developed. Olefins of the type R cH=CHR react with hexafiuoroacetone azine to give azomethine mines, which undergo a sequence of prototropic shifts to form 17/-3-pyrazolines [196, 202], On heating, the latter are transformed into 3-trifluoromethylpyrazoles [196, 206] and, on treatment with bases, into 1,2,5,6-tetrahydropynmidines [206] (equation 45)... 

A. M. del Rio in 1801 claimed to have discovered the previously unknown element 23 in a sample of Mexican lead ore and, because of the red colour of the salts produced by acidification, he called it erythronium. Unfortunately he withdrew his claim when, 4 years later, it was (incorrectly) suggested by the Frenchman, H. V. Collett-Desotils, that the mineral was actually basic lead chromate. In 1830 the element was rediscovered by N. G. Sefstrom in some Swedish iron ore. Because of the richness and variety of colours found in its compounds he called it vanadium after Vanadis, the Scandinavian goddess of beauty. One year later F. Wohler established the identity of vanadium and erythro-nium. The metal itself was isolated in a reasonably pure form in 1867 by H. E. Roscoe who reduced the chloride with hydrogen, and he was... 

As a result, we could open the door to a new frontier in indole chemistry. Various 1-hydroxyindoles (4a), l-hydroxytryptophans(la), 1-hydroxytryptamines (lb), and their derivatives have been given birth for the first time. As predicted, 1-hydroxytryptophan and 1-hydroxytryptamine derivatives are found to undergo previously unknown nucleophilic substitution reactions. In addition, we have been uncovering many interesting reactivities characteristic of 1-hydroxyindole structures. From the synthetic point of view, useful building blocks for indole alkaloids, hither to inaccessible by the well-known electrophilic reactions in indole chemistry, have now become readily available. Many biologically interesting compounds have been prepared as well. 

The previously unknown 2-nitroindoles have been conveniently prepared from o-nitroben-zaldehyde via the Sundberg indole synthesis fEq 10 61 ... 

Plouvier then prepared the previously unknown racemic form of proto-quercitol by mixing equal weights of the two enantiomers. The melting point (237°C.) of the mixture was not depressed, and its (presumably solid state) infrared spectrum reportedly (36) was identical with that of either active form. It thus appears that DL-proto-quercitol exists as a solid solution, not a racemic compound or conglomerate. 

The vapour pressure relations of mixed liquids were cleared up experimentally by the Russian chemist, Dmitri Konowalow (1881) the theory had previously (unknown to Konowalow) been developed by J. Willard Gibbs in 1875. 

On the basis of experimental findings Heinze et al. propose the formation of a particularly stable, previously unknown tertiary structure between the charged chain segments and the solvated counterions in the polymer during galvanostatic or potentiostatic polymerization. During the discharging scan this structure is irreversibly altered. The absence of typical capacitive currents for the oxidized polymer film leads them to surmise that the postulated double layer effects are considerably smaller than previously assumed and that the broad current plateau is caused at least in part by faradaic redox processes. 

We note a limitation of synthesis by P decay. Failing careful structure analysis the possibility remains that a new, previously unknown, structure type is present which, because of its properties being similar to those of another expected compound, may not initially be recognized as a new type of compound. 

Aryl-l,2,4,5-tetrazines are oxidised by methyl(trifluoromethyl)dioxirane to their previously unknown iV-oxides 96. NMR studies have shown that N-l is oxidised regioselectively <96X2377 >. 

Set the task of discovering new, previously unknown druggable receptors, how would we go about it In particular, how would we find a GPCR The first step toward functional annotation of a new GPCR sequence usually involves searching a primary sequence database with pairwise similarity tools. Such searches can reveal clear similarities between the query sequence... 

D. Pseudohalogeno-derivatives.—Little work has been carried out in this area. Isocyanates of cyclic phosphazenes, previously unknown, are thought to be formed in the reaction of NgPaBrg with AgOCN in nitro-methane. They were detected by i.r. spectroscopy, and underwent ready polymerization, which precluded their isolation. On the other hand, isothiocyanates, [NP(NCS)2] (n = 3 or 4), are well known and a detailed study of their spectra has been reported. The azide, N3Pa(N3)8, has been the subject of an i.r. study which suggests that the molecule has Z)3A symmetry. 

OS 71] [no details on reactor] ]P 52] An intermediate, previously unknown, was discovered during micro-channel Schiff base formation [127]. 

The NHCs have been used as ligands of different metal catalysts (i.e. copper, nickel, gold, cobalt, palladium, rhodium) in a wide range of cycloaddition reactions such as [4-1-2] (see Section 5.6), [3h-2], [2h-2h-2] and others. These NHC-metal catalysts have allowed reactions to occur at lower temperature and pressure. Furthermore, some NHC-TM catalysts even promote previously unknown reactions. One of the most popular reactions to generate 1,2,3-triazoles is the 1,3-dipolar Huisgen cycloaddition (reaction between azides and alkynes) [8]. Lately, this [3h-2] cycloaddition reaction has been aided by different [Cu(NHC)JX complexes [9]. The reactions between electron-rich, electron-poor and/or hindered alkynes 16 and azides 17 in the presence of low NHC-copper 18-20 loadings (in some cases even ppm amounts were used) afforded the 1,2,3-triazoles 21 regioselectively (Scheme 5.5 Table 5.2). 

Figure 24. Measured 6 Tla) vs. Th diagram used to infer the ages of lava flows from Mt. Etna in the age range 0 to 8 ka. The eurves labeled 0, 0.5, 1... ka correspond to isochron curves. The isochron 0 is defined by the 6 Tla)o-Th correlation observed in historical lava flows of the last two millennia (Condomines et al. 1995). Five samples of previously unknown ages are reported in this diagram (Condomines et al. 1995, and unpublished results).

The results presented above indicate that the previously unknown head-to-tail polymerization is the major reaction product of the iminium methide species. To investigate the generality of this reaction, we next studied a neutral ene-imine species shown in Scheme 7.9.48 As illustrated in this scheme, the generation of this reactive species requires quinone reduction followed by elimination of acetic acid. The ene-imine is structurally related to the methyleneindolenine reactive species that is a metabolic oxidation product of 3-methylindole (Scheme 7.9).57 59... 

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