Space-filling models benzene

The metal-ion complexmg properties of crown ethers are clearly evident m their effects on the solubility and reactivity of ionic compounds m nonpolar media Potassium fluoride (KF) is ionic and practically insoluble m benzene alone but dissolves m it when 18 crown 6 is present This happens because of the electron distribution of 18 crown 6 as shown m Figure 16 2a The electrostatic potential surface consists of essentially two regions an electron rich interior associated with the oxygens and a hydrocarbon like exterior associated with the CH2 groups When KF is added to a solution of 18 crown 6 m benzene potassium ion (K ) interacts with the oxygens of the crown ether to form a Lewis acid Lewis base complex As can be seen m the space filling model of this... 

The connection between a molecule s electron density surface, an electrostatic potential surface, and the molecule s electrostatic potential map can be illustrated for benzene. The electron density surface defines molecular shape and size. It performs the same function as a conventional space-filling model by indicating how close two benzenes can get in a liquid or crystalline state. 

Fig. 26 Crystallographic packing in PhBABI (left), including solvated voids (right, solvent hexane and benzene shown as space-filling models).

Figure 11 shows a space-filling model of the nonstrained, yet extremely overcrowded, radical PTM-, with its propeller-blade-like pentachlorophenyl groups. It may also be noted that the central trivalent carbon is completely shielded by the six o-chlorines and the three benzene rings. The normally reactive radical site, its central carbon atom where most of the electron spin density resides, is enveloped in a cage of carbons and chlorines, and is unable to approach within the chemical-bonding distance of other molecular species. Furthermore, no molecular distortion, no matter how extensive, would allow any additional medium-sized atom or group to be accommodated on the a-carbon. 

Ball-and-stick and space-filling models of benzene. 

Recall that the resonance structures indicate that the true structure of benzene is an average between the two structures. In other words, all carbon-carbon bonds in benzene are equivalent and are midway between a single and double bond. The space-filling model of benzene is ... 

The space-filling model of benzene shows that all carbon-carbon bond distances are identical. 

The simplest aromatic hydrocarbon is benzene, CgHg. Chemists have struggled for decades to find a structural diagram for benzene that is consistent with its physical and chemical properties, but without success. Common forms and its space-filling model are... 

The barium bis(dnunod) complex is readily prepared by a redox reaction combining elemental barium with Hdnunod (equation 43). Purified by distillation of the excess Hdnunod, Ba(dmmod)2 was identified to be authentic by elemental analysis, and found to be monomeric in benzene solution. Examination of the literature reports currently available indicates that this represents the first observation of an ambient condition liquid barium compound that is based on )3-diketonate ligands. Utihzing the data, it would appear that the metal center is six coordinate. Examination of space-filling molecular models lends some credence to this suggestion. 

According to space-filling scale models, the molecules of chlorocarbons with the alkyl substituent flanked by two o-chlorines, such as perchlorotoluene, perchloroethylbenzene, perchloro-p-xylene and perchlorobi-p-tolyl, are highly strained (pp. 273, 274). In order to partly relieve that strain, some bending of bonds in the benzene ring takes place strained benzenes of this type are frequently severely distorted. In many cases, this has been ascertained by X-ray structural measurements. 

Use a molecular mechanics program to generate energy-minimized structures and estimate the hydrodynamic radii of benzene and monochlorobenzene. For diatomic molecules, covalent and van der Waals radii are useful to calculate molecular size. From a molecular mechanics viewpoint, space-filling molecular models illustrate the van der Waals radius of each atom in the molecule. Use these hydrodynamic radii to calculate liquid-phase diffusion coefficients via the Stokes-Einstein equation. 

---