Angular molecules

It is generally true that a divalent atom with two p orbitals as valence orbitals forms an angular molecule. Since this prediction is reliable, the bonding is usually characterized by identifying the valence orbitals. Oxygen is said to use p5 (read, p two ) bonding in water and FjO. 

The compound SnCl2. which appears superficially to be similar to Be( l2. actually is different because P - 3, which leads to a triangular coplanar electron-pair geometry. Here, however, BP = 2 and LP = I. and the net result is that SnCI2 is an angular molecule (Figure 9-3) rather than a linear one. 

Still another type of molecule exists for P = 4 water 18 examPle (Flgure 9-7). Here, BP = 2, and LP = 2. The net result is an angular molecule with the two lone pairs occupying tetrahedral positions in the electron-pair geometry. 

In cases where the various factors controlling regiospecificity are in conflict, mixtures of products may arise. Thus 1,3,5-trihydroxyxanthone affords a mixture of the chromenes (79) and (80) <70JCS(C)1662). The transition state leading to the linear chromene allows retention of the chelate stabilization with loss of pyranone resonance, whilst the reverse situation obtains in the formation of the angular molecule. 

The angular molecule has the following symmetry operations (symmetry C2V) ... 

Exercise 21-24 a. Sulfur dioxide is an angular molecule that can be represented as having a nonbonding electron pair in an sp2 hybrid orbital and one vacant p orbital on sulfur. Use this formulation to derive a thermally allowed transition state for the reversible 1,4-cycloaddition of S02 to 1,3-butadiene (Section 13-3C). b. The three-membered ring sulfone, shown below, is very unstable and rapidly dissociates to S02 and ethene. This process is used for the synthesis of alkenes by the dissociation of cyclic sulfones (Ramberg-Backlund reaction). Determine whether the transition state for the thermally favorable reaction is conrotatory or disrotatory. 

Step 3. This results in an angular molecule as shown in Table 9.2. The electron group geometry is tetrahedral. 

The double bond is considered one electron group, the single bond is another, and the lone pair is a third. The three groups arrange themselves as far apart as possible 120°. The addition of the oxygen atoms results in an angular molecule ... 

In the course of a recent low-temperature study of the system S/Cl it was possible to prepare single crystals of SCI2 and to determine the solid-state structure at - 134°C (233). As shown in Fig. 26, there are two independent angular molecules in the unit cell that are weakly associated through S--C1 and S---S contacts to form bimolecular layers and that have intramolecular dimensions very close to the values of the free gaseous molecule (322,432) (Table 11). Additional literature on properties of the chalcogen dihalides is abstracted in (160). 

Structural details of the angular molecules SCI2 and TeBr2 are included in Table 16.2. 

Sulfur dioxide is a colorless, poisonous, corrosive gas with a very irritating odor. Even in small quantities, it causes coughing and nose, throat, and lung irritation. It is an angular molecule with trigonal planar electronic geometry, sp hybridization at the S atom, and resonance stabilization. 

If we recall that H2O is an angular molecule with the following Lewis structure,... 

Ref. (6).f The most important consequence of weak localization on alumina is a resulting preference for the adsorption of linear Of near-line sample molecules. A linear molecule such as anthracene is better able to align with a linear row of adsorbent sites than is an angular molecule such as phenanthrene. As a result anthracene is adsorbed ort alumina more-strongly than is its isomer phenanthrene. ... 

Water is an angular molecule with an H-O-H bond angle of 104.5° and an O-H bond length of 0.96 A. The energy of dissociation of the O-H bond is about 450 kJ/ mol, much higher than that for typical C-C bonds which average around 350 kJ/ mol. 

Fig. 3.17 The reactivity of a series of benzooxirenes was studied by semiempirical, ab initio and DFT methods [91], The numbers over the arrows are the activation energies (kJ mol ) for conversion to the oxo carbenes, calculated by a DFT method. 21-24 are drawn with a resonance form that maximizes the number of benzenoid rings this forces the formal oxirene rings to be formally dimethyleneoxirane moieties in the linear 21 and 23, and oxirene moieties in the angular 22 and 24. Comparing the linear with the angular molecules, former have much higher calculated barriers to rearrangement...

Ethyl chloride. . C2H6CI 192 66.0 50.1 75,9 1 angular molecule according... 

Anthracene and phenanthrene (Fig. 14.14) are isomers. In anthracene the three rin are fused in a linear way, and in phenanthrene they are fused so as to produce an angular molecule. Both of these molecules also show large resonance energies and chemical properties typical of aromatic compounds. 

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