Electron-rich atom

Charge-Transfer Forces. An electron-rich atom, or orbital, can form a bond with an electron-deficient atom. Typical examples are lone pairs of electrons, eg, in nitrogen atoms regularly found in dyes and protein and polyamide fibers, or TT-orbitals as found in the complex planar dye molecules, forming a bond with an electron-deficient hydrogen or similar atom, eg, —0 . These forces play a significant role in dye attraction. 

The molecule below has four stereoisomeric forms exoO exoCH2Br, exoO endoCH2Br, and so on. Examine electrostatic potential maps of the four ions and identify the most nucleophilic (electron-rich) atom in each. Examine the electron-acceptor orbital (the lowest-unoccuped molecular orbital or LUMO) in each and identify electrophilic sites that are in close proximity to the nucleophilic. Which isomers can undergo an intramolecular E2 reaction Draw the expected 8 2 and E2 products. Which isomers should not readily undergo intramolecular reactions Why are these inert ... 

What does functional-group polarity mean with respect to chemical reactivity Because unlike charges attract, the fundamental characteristic of all polar organic reactions is that electron-rich sites react with electron-poor sites. Bonds are made when an electron-rich atom shares a pair of electrons with an electron-poor atom, and bonds are broken when one atom leaves with both electrons from the former bond. 

Hydrolysis Reactions. Hydrolysis reactions involve cleavage of a single bond by reaction with water, a hydronium, or a hydroxide ion (78). The bond is typically polarized between an electron-deficient atom (C in carbonyl, P in organophosphates) and an electron-rich atom (0, Cl, Br). The reaction may be neutral, base-, or acid-promoted, depending on the substrate properties and the reaction conditions, such as pH, temperature, and ionic strength (78, 79). 

The basic idea behind these reactions is the same An electron-rich atom with a lone pair (a nucleophile) donates that lone pair to an electron-poor atom (an electrophile). 

These are molecules, which have an electron-rich atom. They are therefore electron donating and tend to react with electrophiles. 

Some atoms are more electronegative than others that is, they more strongly attract electrons. The relative electronegativities of atoms encountered in this text are F > O > N > 0 S > P 11. For example, the two electron pairs making up a 0=0 (carbonyl) bond are not shared equally the carbon is relatively electron-deficient as the oxygen draws away the electrons. Many reactions involve an electron-rich atom (a nucleophile) reacting with an electron-deficient atom (an electrophile). Some common nucleophiles and electrophiles in biochemistry are shown at right. 

Other possible ambident nucleophiles include cyanide anion (CN ), methyl sulfinate anion (CH3S02 ), and acetone enolate (CH3COCH2 ). Identify the most electron-rich atom(s) in each anion (based on charges alone), and indicate the major product that should result from an SN2 reaction with methyl bromide at this atom(s). 

These reactions are the results of the complexing of the electron-poor atoms of the acid with the electron-rich atoms of the base through the lone pain of the latter. Thus ... 

Electrophilic species that are positively charged or have a partial positive charge and therefore a tendency to bond to electron-rich atoms and functional groups, particularly N, O, and S, that abound on nucleic acids and proteins (including proteinaceous enzymes), which are commonly... 

An additional complication affecting silicon surface chemistry is the well-established fact that dimers tilt away from the symmetric position (c.f. Fig. 1(b)). Associated with dimer tilting is a charge transfer from the down atom to the up atom. Hence, the dimers exhibit somewhat zwit-terionic character, with one electron-poor atom and one electron-rich atom. Such a property of the Si(100)-(2 x 1) surface makes it possible to use nucleophilic and electrophilic attachment reactions. At temperatures less than 120 K, dimer tilting on Si(100)-(2 x 1) can be observed in STM experiments [3,9], while at higher temperatures the direction of the tilt oscillates on a time scale faster than the order milliseconds sampling times of the STM. 

Most organic reactions are ionic. Electrons move from an electron-rich atom towards an electron-poor atom anions or cations are intermediates. Formation of a cyclic ester (a lactone) is an example. 

Almost all compounds polymerizing by the radical mechanism belong to the classical monomers with a double or triple bond. Radicals of relatively low reactivity formed from the initiators do not usually attack the bonds of electron-rich atoms (with an excess of electrons). They react readily with electron-deficient atoms. Thus the anionically polymerizing monomers usually also polymerize by a radical mechanism. Typical cationic monomers do not undergo radical polymerization. The quite neutral ethylene forms a transition between the two groups. It polymerizes reluctantly by the radical and ionic mechanisms cationically it only yields oligomers. 

Coordinate bonding is another type of direction-specific interaction. This type of interaction occurs between metal ions and electron-rich atoms and is of moderate strength. Such interactions have also been utihzed in the formation of supramolecular assemblies, and several examples are given in Chap. 3. 

Figure 2.1 The contiriuum in bonding from covalent to ionic is a result of an unequal distribution ot bonoing electrons between atoms. The symbol 8 (lowercase Greek delta means part/a/charge, either partial positive ((S+) for the electron-poor atom or partial negative (o-) fnr the electron-rich atom.

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