Bent shape

The H3 and molecules are special cases of AH2 molecules in that neither of them has the linear or bent shape already discussed. They are both cyclic molecules although H3 is known only in excited electronic states since, in its ground state, it is unstable with respect to H + H2. 

Quartz, a common form of silica, is a network of Si—O bonds. Silicon and oxygen both have tetrahedral electron group geometry. All the silicon atoms have tetrahedral shapes and all the oxygen atoms have bent shapes. 

A polymeric structure is also observed in the adduct LE 2I2 (LE = 4,5-6z s(bromomethyl)l,3-dithiole-2-thione). LE-I2- I2 bent-shaped units, which are typical in discrete extended spoke adducts with 1 2 (LE/I2) stoichiometry, are joined head-to-tail by soft-soft I- -I interactions involving the terminal iodide atom of the LE-I2 moiety and the terminal iodide atom of the second coordinated di-iodine molecule.37... 

This determination of the molecular geometry of carbon dioxide and water also accounts for the fact that carbon dioxide does not possess a dipole and water has one, even though both are composed of polar covalent bonds. Carbon dioxide, because of its linear shape, has partial negative charges at both ends and a partial charge in the middle. To possess a dipole, one end of the molecule must have a positive charge and the other a negative end. Water, because of its bent shape, satisfies this requirement. Carbon dioxide does not. 

Fullerenes are cage-like carbon structures which derive from a graphene sheet where a few six-membered rings are replaced by five-membered ones which forces the layer into a bent shape. Placing the pentagons at suitable positions, a spherical structure of 60 carbon atoms is obtained - the buckminsterfullerene. Fullerenes with... 

Polarity of functional group The bent shape around the oxygen atom in an ether means that the two C—0 dipoles do not counteract each other. Because a C—0 bond is less polar than an 0—H bond, an ether is less polar than an alcohol. 

What VSEPR notations correspond to a molecule that have a bent shape ... 

The discussion of the distortion of the water molecule from a linear to a bent shape allows a tentative general conclusion to be reached. This is that if a distortion of a molecule from a particular symmetry allows two MOs to mix, so that the lower occupied orbital is stabilized at the expense of the higher vacant orbital, such a distortion will occur and will confer stability on the distorted molecule. A gain of stability will only occur if the two orbitals concerned in the stabilization process are the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO).. If both orbitals are doubly occupied, interaction between them does not lead to any change in stability. The generality of this conclusion is explored further in the next sections of this chapter and in Chapter 6. 

The idea that distortion of a triatomic molecule from a linear to a bent shape occurs if the HOMO and LUMO are of the same symmetry representation, so that electrons in the HOMO are stabilized, was discussed as a tentative general approach to molecular shape. 

MO treatment would use Figure 5.20 and the accommodation of the 19 valence electrons (seven from Cl and six each from the oxygen atoms) would be best in the bent shape using orbitals on the right-hand side of the diagram. The strongly angle-dependent 6a, orbital would be occupied and that would stabilize the bent ion. 

H 0 also has polar bonds. However, since there is a net dipole moment, the individual bond moments do not cancel, and the molecule must have a bent shape ... 

Because valence electron octets are so common, particularly for second-row elements, the atoms in a great many molecules have shapes based on the tetrahedron. Methane, for example, has a tetrahedral shape, with H-C-H bond angles of 109.5°. In NH3, the nitrogen atom has a tetrahedral arrangement of its four charge clouds, but one corner of the tetrahedron is occupied by a lone pair, resulting in a trigonal pyramidal shape for the molecule. Similarly, H20 has two corners of the tetrahedron occupied by lone pairs and thus has a bent shape. 

Fig. 1 Due to their strongly bent shape and the excluded volume effects bent-core molecules tend to form polar layers, v is the layer normal and p the electric polarization...

Bedel JP, Rouillon JC, Marcerou JP, Nguyen HT, Achard MF (2004) Evidence for different polymorphisms with and without an external electric field in a series of bent-shaped molecules. Phys Rev E 69 061702... 

Gorecka E, Pociecha D, Mieczkowski J, Matraszek J, Guillon D, Donnio B (2004) Axially polar columnar phase made of polycatenar bent-shaped molecules. J Am Chem Soc 126 15946-15947... 

Essentially, the origin of spontaneous chiral resolution is the same as the previous example. When molecules with the same chiral conformation form small chiral domains due to packing entropy effects, the same chiral conformation of molecules is stabilized when they approach the chiral domain. Thus both chiral domains with different chiral conformations grow, resulting in spontaneous chiral resolution [6-8]. Chirality enhancement occurs even in such chiral domains. For instance, chirality in both segregated chiral domains is enhanced by doping nonchiral bent-shaped molecules (BSMs) with nonchiral rod-shaped molecules (RSMs), as observed by circular dichroism (CD) or optical rotatory power (ORP) [9],... 

Experimental Observation of Enhanced Chirality in Chiral Phases by Achiral Bent-Shaped Molecules... 

Fig. 3 Inverse structural pitch (1/nP) as a function of dopant ratio. Bent-shaped molecule P12-0-PIMB enhances the twisting power, which is proportional to 1/nP, whereas rod-shaped molecule TBBA gives just a dilution effect the helical pitch increases...

Fig. 4 Selective reflection wavelength (optical pitch) as a function of temperature for three samples host material showing SmC and SmCA without dopant, with 1% and 3% dopant The chemical structures of the rod-shaped host and the bent-shaped dopant molecules are also shown. As shown in inset, inverse pitch increases almost linearly with dopant content [4]...

Fig. 5 Induction of the blue phase by doping a N material with (a) a rod-shaped molecule MHPOBC and (b) a bent-shaped molecule P8-PIMB. In both cases, the blue phase is induced above the N phase. The bent-shape of the antiferroelectric molecule is responsible for the blue phase induction in (a), since the doping of a real rod-shaped molecule (TBBA) does not induce the blue phase [26]...

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