Planar arrangement

Section 1 10 The shapes of molecules can often be predicted on the basis of valence shell electron pair repulsions A tetrahedral arrangement gives the max imum separation of four electron pairs (left) a trigonal planar arrange ment is best for three electron pairs (center) and a linear arrangement for two electron pairs (right)... 

The structural features especially the very polar nature of the carbonyl group point clearly to the kind of chemistry we will see for aldehydes and ketones in this chapter The partially positive carbon of C=0 has carbocation character and is electrophilic The planar arrangement of its bonds make this carbon relatively uncrowded and susceptible to attack by nucleophiles Oxygen is partially negative and weakly basic... 

What structural features are responsible for the reactivity order of carboxylic acid derivatives Like the other carbonyl containing compounds that we ve studied they all have a planar arrangement of bonds to the carbonyl group Thus all are about the same in offering relatively unhindered access to the approach of a nucleophile They differ m the degree to which the atom attached to the carbonyl group can stabilize the carbonyl group by electron donation... 

Mesomerism involving polarized and nonpolarized contributing enamine forms influences the enamine s spectral properties and chemical reactivity. For mesomerism to be present, a planar arrangement is required for the three atoms of enamine grouping and the five atoms immediately bound to this system. If this condition is not fulfilled, full interaction of the tt electrons of the double bond with the free electron pair on the nitrogen atom is impossible. Enamines in which mesomerism is inhibited do not show the properties characteristic of enamines, and only the mutual electrostatic interaction of the double bond and lone electron pair of the nitrogen atom can be observed. Such steric hindrance of mesomerism occurs mainly in polycyclic systems. 

Figure 11.4 The transition state of an Sjvj2 reaction has a planar arrangement of the carbon atom and the remaining three groups. Electrostatic poten tial maps show that negative charge (red) is delocalized in the transition state.

Developing electron-deficient orbital Is stabilized by conjugation with jc-orbita in a planar arrangement... 

FIGURE 3.6 The square planar arrangement of atoms taken up in AX4E, molecules the two lone pairs are farthest apart when they are on opposite sides ol the central atom. 

Answer Three cr-bonds formed from F2/7c-orbitals and B2s/r hybrids in a trigonal planar arrangement]... 

Calculate the radius of the cavity formed by three circular disks of radius r that lie in a dose-packed planar arrangement. Check your answer experimentally by using three compact disks and measuring the radius of the cavity that they form. 

The double bond in alkenes makes them more rigid than alkanes. Some of the atoms of alkene molecules are locked into a planar arrangement by the TT-bond hence, they cannot roll up into a ball as compactly as alkanes can. Because they do not pack together as compactly as alkanes do, they have lower boiling and melting points. 

Fig. 11. Possible planar arrangements of poly(tetrahydropyran-2,6-diylimino-carbonyl) molecules provided all hydrogen bonds are ideally regularly formed between the chains58)...

Note that (35) must be the stereoisomer with Ph and Cl trans for the anti-peri-planar arrangement required for the stereospecific rearrangement, and so the GrIgnard addition must be highly stereoseleetive. This all makes sense by con formatlonal analysis. 

KMg3(AlSi3 Oio) (0H)2 —contain sheets in which every fourth silicon atom is replaced by an aluminum atom. Because of the planar arrangement of its aluminosilicate network, mica is easily broken into flakes. Figure 9-19 includes a photograph of mica. 

Each heme unit in myoglobin and hemoglobin contains one ion bound to four nitrogen donor atoms in a square planar arrangement. This leaves the metal with two axial coordination sites to bind other ligands. One of these sites is bound to a histidine side chain that holds the heme in the pocket of the protein. The other axial position is where reversible binding of molecular oxygen takes place. 

As we turn to complexes with only four groups bound in a planar arrangement and two potential coordination positions open it should not be too surprising... 

Fig. 9 Honeycomb-like architectures formed on self-assembly of halide anions (which work as tridentate XB acceptors and sit at the networks nodes) with 1,4-DITFB (which works as bidentate donor and forms network sides) (A). The angles formed by the XBs around the halide anions determine the corrugation of the honeycomb architecture, a more planar arrangement around the halide anions (as is the case of the iodide anions in adduct l,4-DITFB/Me4P+r (B) with respect to the bromide anions in adduct l,4-DITFB/Ph4P+Br (C)) results in a less corrugated honeycomb architecture...

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