Group occurrence

Tallstedt L, Lundell G, Torring O, Wallin G, Ljunggren JG, Blomgren H, Taube AThe Thyroid Study Group. Occurrence of ophthalmopathy after treatment for Graves hyperthyroidism. N Engl J Med 1992 326(26) 1733-8. 

In 2011, a group of Department of Natural Drugs, Faculty of Pharmacy, University of Veterinary and Pharmaceutical Sciences Brno, Brno, Czech Republic identified a novel isoflavanone 2, 2,5-trimethoxy-6,7-methylenedioxyisoflavanone (12) (Figure 4) with first a methoxy group occurrence at position 2 of the isoflavanone skeleton, together with tlatlancuayin (2 ,5-dimethoxy-6,7-methylenedioxyisoflavone, 10) from the aerial parts of a non-cold resistance perennial foliage plant Iresine herbstii in the amaranth family, Amaranthaceae by spectroscopic analysis. 

It has been postulated that intramolecular rather than intermolecular chain-transfer contributes the predominant reaction in a solution of living poly(methyl-phenylsiloxane), and poly(dimethylsiloxane) with trimethylsilyl end-blocked groups. Occurrence of the intramolecular reaction, leading to formation of cyclic compounds of various sizes, was ascribed to the flexibility of siloxane chains. 

Space Group % Occurrence Crystal System Z Degrees of Freedom Cell Trans. Rot. Total... 

Hydroperoxide / -H0(0)CPhC(CH3)200H in which hydroperoxide moiety is directly connected with aromatic ring shows the highest reactivity. Aliphatic group occurrence between hydroperoxide moiety and aromatic ring leads to the decrease o/hydroperoxide reactivity in the reaction of catalytic decomposition in the presence of Et NBr. According to the values listed in Table 2 the reactivity of the complex-bonded hydroperoxides increases as follows phCH2C(CH3)2 OOH < Ph(CH2)2C(CH3)2 OOH... 

Figure Bl.25.9(a) shows the positive SIMS spectrum of a silica-supported zirconium oxide catalyst precursor, freshly prepared by a condensation reaction between zirconium ethoxide and the hydroxyl groups of the support [17]. Note the simultaneous occurrence of single ions (Ff, Si, Zr and molecular ions (SiO, SiOFf, ZrO, ZrOFf, ZrtK. Also, the isotope pattern of zirconium is clearly visible. Isotopes are important in the identification of peaks, because all peak intensity ratios must agree with the natural abundance. In addition to the peaks expected from zirconia on silica mounted on an indium foil, the spectrum in figure Bl. 25.9(a)...

Structural keys describe the chemical composition and structural motifs of molecules represented as a Boolean array. If a certain structural feature is present in a molecule or a substructure, a particular bit is set to 1 (true), otherwise to 0 (false). A bit in this array may encode a particular functional group (such as a carboxylic acid or an amidelinkage), a structural element (e.g., a substituted cyclohexane), or at least n occurrences of a particular element (e.g., a carbon atom). Alternatively, the structural key can be defined as an array of integers where the elements of this array contain the frequency of a specific feature in the molecule. 

The group contribution method allows the approximate calculation of solubility by summing up fragmental values associated with substmctural units of the compounds (see Section 7.1). In a group contribution model, the aqueous solubility values are computed by Eq. (12), where log S is the logarithm of solubility, C is the number of occurrences of a substmctural group, i, in a molecule, and is the relative contribution of the fragment i. 

As a guide to the probable occurrence of a constant-boiling mixture, it should be noted that such mixtures most frequently occur when one of the components contains an hydroxyl (— OH) group. Only aqueous and alcoholic mixtures therefore are likely to have a constant boiling-point. 

The lists are arranged according to the occurrence of functional groups. 

Since all A groups have the same reactivity by hypothesis, the probability of this occurrence is simply p. 

Occurrence. Niobium and tantalum usually occur together. Niobium never occurs as the metal, ie, ia the free state. Sometimes it occurs as a hydroxide, siUcate, or borate most often it is combiaed with oxygen and another metal, forming a niobate or tantalate ia which the niobium and tantalum isomorphously replace one another with Htde change ia physical properties except density. Ore concentrations of niobium usually occur as carbonatites and are associated with tantalum ia pegmatites and alluvial deposits. Principal niobium-beariag minerals can be divided iato two groups, the titano- and tantalo-niobates. 

The pareto chart, tool number six, is a special type of histogram (48) where the frequency data is grouped in order of decreasing occurrence or other measures of importance rather than in sequential or numerical order. The chart, an example of which is shown in Figure 6, illustrates the causes in decreasing order of importance. It enables the improvement effort to be focused where it can have the most impact and is an effective management communication tool. 

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