Hydrogen atom electron cloud

An electrophile (E+) reacts with the benzene ring and substitutes for one of its six hydrogen atoms. A cloud of tt electrons exists above and below the plane of the benzene ring. These tt electrons are available to electrophiles. Benzene s closed shell of six tt electrons gives it a special stability. 

The size and shape of an electron cloud is described by the electron density (the number of electrons per unit volume). Consider a graph of electron density in the hydrogen atom as a function of distance from the nucleus. 

The natural orbitals %2v and %3p are, in contrast to the hydrogenlike functions, localized within approximately the same region around the nucleus as the Is orbital. This means that the polarization caused by the long-range interaction is associated mainly with an angular deformation of the electronic cloud on each atom. If %2p and %3p are expanded in the standard hydrogen-like functions, an appreciable contribution will again come from the continuum. 

Astrophysicists believe that the early universe was composed mostly of hydrogen. As a cloud of hydrogen collapses, heating breaks its hydrogen atoms into a plasma of protons and electrons. A first-generation star forms... 

Therefore, electrons adjust their state to any instant position of the proton and solvent polarization in both the initial (hydroxonium ion) and final (adsorbed hydrogen atom) states. The proton in the hydroxonium ion sees an average electron cloud but feels any instant configuration of solvent polarization. 

Two structures are possible for the interaction of aromatic hydrocarbons with acids.270 In the a-structures a covalent bond is established between the acidic reagent and a particular carbon atom of the benzene ring. The a-structures are essentially classical carbonium ions. In the -structures a non-classical bond is established, not to any particular atom, but to the -electron cloud in general. It is quite likely that both types of structure are represented by actual examples. Thus m-xylene interacts more strongly with hydrogen chloride than does o-xylene, but the difference between the two hydrocarbons is much more pronounced when their interactions with a boron trifluoride-hydrogen fluoride mixture are compared. This is readily understandable... 

The peculiar behavior of H might be relevant to understand the hydrogen bond, which deforms the electronic cloud of the proton. On the other hand, it is surprising to discover an anomalous behavior for a closed-shell atom like He. However, it has been demonstrated in helium-atom-scattering that interactions between He atoms... 

A) almost equals the van der Waals distance. As in [2.2]para-cyclophane, the hydrogen atoms of the aromatic moieties are directed towards the interior of the molecule because of the increased -electron density on the outside of the molecule caused by the intraannular interaction of the 7r-electron clouds. 

Hydrogen bonds are due to the attractive forces between the distorted electron cloud of a hydrogen atom and other more electronegative atoms such as oxygen and nitrogen. The attractive forces are weaker than covalent bonds, but many hydrogen bonds can be formed in macromolecular protein molecules. Van der Waals forces are weaker attractive forces, due to the attraction between neutral atoms. 

The next two columns now give the monovalent structural radii r, and the ratio of these to the r.m.s. electron-cloud radii y. This ratio is about two for most ions and rather larger for the inert gases, but oiJy about unity for the covalently bound atoms smaller still for the special case of hydrogen). 

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