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Ribbon orbitals

The Pauli and aufbau principles dictate where the cuts occur in the ribbon of elements. After two electrons have been placed in the 1. S orbital (He), the next electron must go in a less stable, n — 2 orbital (Li). After eight additional electrons have been placed in the 2 S and 2 p orbitals (Ne), the next electron must go in a less stable, = 3 orbital (Na). The ends of the rows in the periodic table are the points at which the next electron occupies an orbital of next higher principal quantum number. [Pg.515]

The periodic table provides the answer. Each cut in the ribbon of the elements falls at the end of the p block. This indicates that when the n p orbitals are full, the next orbital to accept electrons is the ( + 1 )s orbital. For example, after filling the 3 orbitals from A1 (Z = 13) to Ar (Z = 18), the next element, potassium, has its final electron in the 4 S orbital rather than in one of the 3 d orbitals. According to the aufbau principle, this shows that the potassium atom is more stable with one electron in its 4 orbital than with one electron in one of its 3 (i orbitals. The 3 d orbitals fill after the 4 S orbital is full, starting with scandium (Z = 21). [Pg.517]

For this qualitative problem, use the periodic table to determine the order of orbital filling. Locate the element in a block and identify its row and column. Move along the ribbon of elements to establish the sequence of filled orbitals. [Pg.518]

Convection mixers use a different principle for blending. These mixers have an impeller. This class includes ribbon blenders, orbiting screw blenders, vertical and horizontal high-intensity mixers, as well as diffusion blenders with an intensifier bar. Scale-up considerations are similar to those for the tumble blenders. [Pg.322]

Solid—solid blending can be accomplished by a number of techniques. Some of the most common include mechanical agitation which includes devices such as ribbon blenders, impellers, paddle mixers, orbiting screws, etc a rotary fixed container which includes twin-shell (Vee) and double-cone blenders and fluidization, in which air is used to blend some fine powders. [Pg.562]

Another characteristic property of the electron density of 1 is its relatively high value at the centre e of the ring (more than 80% of that at the CC bond critical point). Density is smeared out over the ring surface and concentrated at its centre because of the occupation of the w0 -orbital (MO 8, 3a(, Figure 6), which has the character of a surface orbital . Cremer and Kraka9, n 13 have termed this phenomenon surface delocalization of electrons, to be distinguished from ribbon delocalization and volume delocalization of electrons (Figure 12)12. [Pg.67]

Figure 21-15 Normal (Hiickel) and Mobius rings of 7r orbitals. To clarify the difference between the two rings, visualize a strip of black-red typewriter ribbon, the black representing the + phase, and the red the — orbital phase. Now join the ends together without, or with, one twist in the strip. At the joint there then will be no node (left) or one node (right). Figure 21-15 Normal (Hiickel) and Mobius rings of 7r orbitals. To clarify the difference between the two rings, visualize a strip of black-red typewriter ribbon, the black representing the + phase, and the red the — orbital phase. Now join the ends together without, or with, one twist in the strip. At the joint there then will be no node (left) or one node (right).
When a cyclic polyene is large enough, it can exist in both cis- and iraws-forms. Our approach to polyene cyclization has tacitly assumed an all cis -n chain in the form of a band or ribbon that would slip smoothly on to the surface of a cylinder of appropriate diameter. Should the orbitals of the two polyenes in (36) have a mismatch in their orbital symmetries, a single twist in the tt band of one of them could remedy this (Fig. 10c). Cycloaddition would now be allowed and the reaction would proceed, provided other factors were favorable. Such cases of Mobius (Zimmerman, 1966), anti (Fukui and Fujimoto, 1966b) or axisymmetric (Lemal and McGregor, 1966), as opposed to Hiickel, syn, or sigma-symmetric ring closure are unknown (or, at least, rare). A Mobius form has, however, been proposed as the key intermediate in the photochemical transformations of benzene (Farenhorst, 1966) in (48) in place of the disrotatory cyclization proposed by van Tamelen (1965). [Pg.222]

Pseudosymmetry of ribbon s orbitals. In our following discussion we shall be looking for symmetry of ribbon s orbitals in the case of reflection in the plane V (Fig. 23). [Pg.79]

Glassification of ribbons. Now let us pass from the classification of molecular orbitals of polyene fragments to classifying the ribbons. It can be done in different ways. Sometimes it is sufficient to indicate only the number of ji-electron centres (n) and the charge (2) of a polyene, denoting each ribbon by the symbol Then, for example, the fragment... [Pg.80]

First, we shall connect only two ribbons and only at one location. The result will be a new acyclic polyene fragment. Let us call it intermediate. If the interacting orbitals of the initial ribbons had an identical pseudosymmetry, e.g. 5, they would combine to form two MOs of the intermediate ribbon with different pseudosymmetries, WS and T A. In this case, the energy WS of the intermediate MO is lower, and the energy WA is higher, than the energies of the initial MOs (Fig. 26a). The same is true when two WA MOs interact (Fig. 266). [Pg.81]

Spirocycles. Now let us turn to the spirocyclic topology of connection of two ribbons. As in the previous case, we shall take into account only the interactions of orbitals possessing identical pseudosymmetry. The new topology, however, calls for imposing new restrictions on the ribbon... [Pg.85]

The parentheses signify that we consider first the orbitals of two pericyclic ribbons and then the change of orbital energies after their interaction with the third ribbon is taken into account. The corresponding molecular orbital diagrams are shown in Fig. 30. [Pg.88]

Screwipaddle blenders Ribbon blenders Orbiting screw blenders Planetary blenders... [Pg.168]

Convection blenders reorient groups of particles in relation to one another as the result of mechanical movement, for example, caused by a paddle or a plow. As a result, circulation patterns result in this type of blenders. Subclasses of convection blenders are typically defined by vessel shape and impeller geometry. Ribbon blenders (Fig. 30), planetary blenders (Figs. 31 and 32), orbiting screw blenders (Fig. 33) are examples of convection blenders. High shear mixers comprise another sub-class of convection blenders that will be discussed separately. [Pg.176]

FIG. 21-157 Examples of low-shear mixers used in granulation, (a) Ribbon blender (h) planetary mixer (c) orbiting screw mixer (d) sigma blender (e) double-cone blender with baffles (/) v blender with breaker bar. (See also Solids Mixing. ) [( ) and (d), Chirkot and Propst, in Parikh (ed.). Handbook of Pharmaceutical Granulation Technology, Taylor 6- Francis, 2005.]... [Pg.2366]


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See also in sourсe #XX -- [ Pg.49 ]

See also in sourсe #XX -- [ Pg.49 ]




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