Molecule bent-shaped

In addition to the pear-shaped molecules, bent-shaped molecules were used to illustrate the dipolar origin of the flexoelectric effects in nematic liquid crystals. It was assumed that the constituent molecules of the nematic liquid crystals are free to rotate around their axes, and in the absence of electric fields, their dipole moments average out so the net polarization of the material is zero. However, when liquid crystals made from polar pear- or banana-shaped molecules are subjected to splay or bend deformations, respectively, they can become macroscopically polar, because the polar structures correspond to a more efficient packing of the molecules. It follows from symmetry considerations that the deformation-induced fiexo-electric polarization Pa can be written as ... 

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. 

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. 

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. 

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]...

Fig. 21 Chirality control by circularly polarized light. The molecules used are bent-shaped twin dimer shown in the top, which has azo-linkages at both arms and shows ShiCa to B4-like phase. By CPL irradiation, almost 100% ee is obtained. In the photo taken between decrossed polarizers, only a very tiny darker domain can be seen in the lower region in a 3-mm domain [21]...

Gorecka E, Nakata M, Mieczkowski J, Takanishi Y, Ishikawa K, Watanabe J, Takezoe H, Eichhorm SH, Swager TM (2000) Induced antiferroelectric smectic-CA phase by doping ferroelectric-C phase with bent-shaped molecules. Phys Rev Lett 85 2526-2529... 

Takekoshi K, Ema K, Yao H, Takanishi Y, Watanabe J, Takezoe H (2006) Appearance of a liquid crystalline nematic-isotropic critical point in a mixture system of rod- and bent-shaped molecules. Phys Rev Lett 97 197801-14... 

Figure 8.4. Inversion of 9,10-dihydroanthracene in the excited singlet state, (a) The equilibrium bent shape of excited molecule, (b) the double-well potential for inversion, and (c) the fluorescence excitation spectrum of the jet-cooled molecule. (From Chakraborthy and Choudhury [1990].)...

In a water molecule, the two hydrogen atoms bond to the oxgen atom at an angle of 109.5 degrees to form a bent-shaped molecule. This is because the bonding occurs with oxygen atom electrons in p orbitals. 

Without its bent-shaped molecule, water might be a gas at room temperature and ice might sink in water leaving our world uninhabitable. 

Find a flowering plant that interests you. Look at the root formation, leaf shapes and how they are attached to the stem, and the shape of the flower. Draw these different shapes. Find molecules that resemble these different shapes. Remember that group 3A elements form trigonal planar shaped molecules, group 4A elements form tetrahedral shaped molecules, group 5A elements form pyramid shaped molecules and group 6A elements form bent shaped molecules. Carbon chains have a zigzag shape and the DNA molecule is a double helix. You will see that these molecular shapes are duplicated in natural objects. See how many molecular shapes you can find in an ordinary flower. 

Figure 10 Reorientation of an azobenzene dye by photoisomerization with polarized light. Molecular representations of the lruns and cis forms of an azobenzene are represented by straight and bent shapes to illustrate how a trans-cis-trans cycle can effect a reorientation of the traru-azobenzene. If the inducing hght is polarized in the horizontal direction, the vertically oriented molecule will be unable to absorb the hght, and this orientation will therefore be photostable.

It is this bent shape of the water molecule that is responsible for its solvent power for so many salts. We speak of the water molecule as a dipole because its center of positive charge and negative charge are located at different points in space as shown ... 

In a water molecule, there are four electron pairs around the oxygen atom. Two of these pairs bond with the hydrogen. The electron pairs are arranged in a shape that is nearly tetrahedral. When you draw the molecule, however, you draw only the oxygen atom and the two hydrogen atoms. This is where the bent shape comes from, as you can see in Figure 3.28. 

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