Partially selected atom

An adjustable atom or bond is one that is selected. A frozen atom or bond is one which is not selected. A partially selected atom is a selected atom, some but not all of whose bonds are selected. For such an atom, the angle between each pair of circularly contiguous frozen bonds is preserved, whereas angles to the nonfrozen bonds are adjusted and optimized relative to the frozen bonds. 

FIGURE 6.17 (a) Total density of states and the partial densities of states projected on selected atomic wave... 

Numerical integration schemes allow an opportunity to test the numerical nonempirical pseudopotentials without their fit by analytical functions, which can lead to a considerable reduction in computational efforts. Employment of atomic pseudopotentials only at some selected atoms of a system while treating the rest all-electronically makes an impression of the consistency and reliability of such a combined approach. The results obtained for the MgO clusters embedded in some effective pseudopotential surroundings demonstrate a promise of the approach for compensation of broken bond effects. Specifically, the approach offers a tool for a substantial reduction of the artificially introduced nonequivalence of partial densities and the effective charges for atoms equivalent in the lattice. It is worth to mention that our approach can be modified further in many ways because numerical integration schemes can be easily applied/adapted even in those cases where the analytical methods become too complicated. 

When sinO/A, increases, both the atomic scattering functions and temperature factors decrease exponentially (see sections 2.11.4 and 2.11.3, respectively). Thus, the unreasonably high isotropic displacement parameters of selected atoms indicate that the scattering ability of the respective sites is reduced. In the title compound, the only reasonable explanation is that the suspected sites are partially occupied. 

RDF. The distance mode dehnes the mode for distance calculation available modes are Cartesian distances, bond-path distances, and topological distances. Descriptors may be calculated on particular atoms. Exclusive mode restricts the calculation to the atom type, and with ignore mode the selected atom type is ignored when calculating the descriptor. In partial-atom mode an atom number has to be given instead of the atom type. The second atom property is available if 2D RDF is selected as code method. 

Two types of reactions were observed with alkylcyclopentanes. A nonse-lective ring opening would cleave each C—C bond (in positions a, b, and c. Fig. 3) in a random way. This was reported for Pt/Al203 with high dispersion (7). A selective splitting, on larger Pt particles, would break di-secondary C—C bonds (6 and c) only (7,20). The splitting close to the tertiary (or quaternary) C atom is hindered to different extent over various metals in most cases, but the total inactivity of this bond is rare (8). A third, partially selective mechanism (7) was also considered, but its possible mechanism was not elucidated sufficiently. 

PFUs are best viewed as bond-based, i.e., as a set of bonds with their adjacent atoms. Note that in case 1, all the PFU s atoms are necessarily frozen or partially selected. In types 2 and 3, the PFU s atoms and bonds are those in the ring system. Two PFUs may not share a bond, though they may have one or more atoms in common. Algorithm 1 is used to calculate the PFUs of first type. The cyclic PFUs are revealed during ring analysis. 

Exercises la. Nucleophilic substitution is a fundamental class of substitution reaction in which an "electron rich" nucleophile selectively bonds with or attacks the positive or partially positive charge of an atom attached to a group or atom called the leaving group the positive or partially positive atom is referred to as an electrophile. 

Table 2. Partial molar volume increments for some selected atomic groups according to Durchschlag and Zipper, based on the data given in Table 1 [94D1],...

Alkyl halides and sulfonates are the most frequently used alkylating acceptor synthons. The carbonyl group is used as the classical a -synthon. O-Silylated hemithioacetals (T.H. Chan, 1976) and fomic acid orthoesters are examples for less common a -synthons. In most synthetic reactions carbon atoms with a partial positive charge (= positively polarized carbon) are involved. More reactive, "free carbocations as occurring in Friedel-Crafts type alkylations and acylations are of comparably limited synthetic value, because they tend to react non-selectively. 

Benzoates. The selective debenzoylation of sucrose octabenzoate [2425-84-5] using isopropylamine in the absence of solvents caused deacylation in the furanose ring to give 2,3,4,6,1/3/6 -hepta- and 2,3,4,6,1/6 -hexa-O-benzoyl-sucroses in 24.1 and 25.4% after 21 and 80 hours, respectively (54). The unambiguous assignment of partially benzoylated sucrose derivatives was accompHshed by specific isotopic labeling techniques (54). Identification of any benzoylated sucrose derivative can thus be achieved by comparison of its C-nmr carbonyl carbon resonances with those of the assigned octabenzoate derivative after benzoylation with 10 atom % benzoyl—carbonyl chloride in pyridine. 

Pyridazine and its 3-methyl and 4-methyl derivatives react with sym-trioxanyl radicals. The reaction takes place selectively at positions 4 and/or 5, and partially at the a-position to a ring nitrogen atom, leading thus to the formylmethylpyridazine derivatives (80JHC1501). 

In our design, divalent Ca was chosen to partially substitute the trivalent atoms, and La and Ce were selected for a trivalent element because their ionic size (rLas+ = l.SOA rce3+=l-48A) was close to that of Ca (rca2+ = T48A) [21]. Like La, the Ce element also generally shows a formal -i-3 oxidation state in in-termetallics. Erom the reactions of the elements, we have identified as major phases the electron-precise/deficient alloys, Ln5.xCaxGe4 (Ln=La, Ce x=3.37,... 

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