Electron-pair bases reaction with

Aromatic amines (p/Cb 9.0-10.0) are considerably weaker bases than are aliphatic amines. Resonance stabilization from interaction of the unshared electron pair on nitrogen with the pi system of the aromatic ring decreases the availability of that electron pair for reaction with an acid. Substitution on the ring by electron-withdrawing groups decreases the basicity of the —NH2 group ... 

Reaction with Co2(CO)g 6.5.2.1 Reaction with electron pair bases 6.2.2.1... 

Reaction with electron pair bases CI5P 12 C215H)H(... 

Mixed-valence compounds. The ground state of monomeric species RM (M = B, Al, Ga, In), which have an electron lone pair at the metal center, is singlet and the singlet-triplet energy gap increases with increasing atomic number. Consequently, these compounds are able to act as Lewis bases. Reactions with Lewis-acidic... 

Because primary aromatic amines are weaker bases/nucleophiles than aliphatic (due to interaction of the electron pair on N with the n orbital system of the aromatic nucleus), a fairly powerful nitrosating agent is required, and the reaction is thus carried out at relatively high acidity. Sufficient equilibrium concentration of unprotonated... 

This step in the reaction has exactly the same form as the Lewis acid-base reaction, with H+ playing the role of the Lewis acid, H20 the role of the Lewis base, and H,0+ the resulting complex. It is this analogy to the behavior of H+ (the species typical of acids) that led to the use of the term acid to describe an electron pair acceptor like BF3. 

The interaction between a metal ion and a ligand can be viewed as a Lewis acid-base reaction, with the ligand donating a lone pair of electrons to an empty orbital on the metal ion to form a coordinate covalent bond ... 

The Bronsted-Lowry definition of a base is an acceptor of protons. Pharmaceutical and biological sciences are concerned mainly with the behaviour of drugs in aqueous systems. Under these conditions, drugs will behave as bases only if they contain a nitrogen atom with a lone pair of electrons available for reaction with protons. The major class of compound to work in this way is the amines. An amine in aqueous solution will react with water to release hydroxide ions (OH-) as shown in equation (3.4). 

Most theories of metal-Ugand bonding consider the Lewis behavior of the species involved. In a Lewis add-base reaction, a pair of electrons from a species is used to form a covalent bond with another spedes. A Lewis base is the species that donates an electron pair, and a Lewis acid is the species that accepts the electron pair. The reaction can be written. 

Boron, a Group 3A element, has three electrons in its valence shell, and after forming single bonds with three fluorine atoms to give BFj, boron still has only sbc electrons in its valence shell. Because it has an empty orbital in its valence shell and can accept two electrons into it, boron trifluoride is electron deficient and, therefore, a Lewis add. In forming the O—B bond, the oxygen atom of diethyl ether (a Lewis base) donates an electron pair and boron accepts the electron pair. The reaction between diethyl ether and boron trifluoride is dassified as an acid-base reaction according to the Lewis model, but because there is no proton transfer involved, it is not classified as an add-base reaction by the Bronsted-Lowry model. Said another way, all Bronsted-Lowry acids are protic acids Lewis adds maybe protic acids or aprotic acids. 

The Fe ion also undergoes a similar Lewis acid—base reaction with cyanide ions. In this case, the Fe ion bonds to the electron pair on the carbon atom of CN . 

The reaction begins with an attack on a hydrogen of the electrophile, HaO", by the electrons of the nucleophilic tt bond. Two electrons from the 7T bond form a new a bond between the entering hydrogen and an alkene carbon, as shown by the curved arrow at the top of Figure 7.6. The carbocation intermediate that results is itself an electrophile, which can accept an electron pair from nucleophilic H2O to form a C-0 bond and yield a protonated alcohol addition product. Removal of H" " by acid-base reaction with water then gives the alcohol product and regenerates the acid catalyst. 

Lewis acid-base behaviour is a simple extension of this idea, with one species providing both electrons and the other species providing a pair of holes (the absence of two electrons in a cloud), so when complex formation occurs, both the former electrons plug the double hole and form a bond. Lewis acid-base reactions are indeed acid-base reactions (with our new definition of acids and bases). 

Ammonia is a two-state system [16], in which the two base states lie at a minimum energy. They are connected by the inversion reaction with a small baiiier. The process proceeds upon the spin re-pairing of four electrons (Fig. 15) and has a very low barrier. The system is analogous to the tetrahedral carbon one... 

When carbon forms four covalent bonds with halogen atoms the second quantum level on the carbon is completely filled with electrons. Most of the reactions of the Group IV tetrahalides require initial donation by a Lewis base (p. 91) (e.g. water, ammonia) which attaches initially to the tetrahalide by donation of its electron pair. Hence, although the calculated free energy of a reaction may indicate that the reaction is energetically favourable, the reaction may still not proceed. Thus we find that the tetrahalides of carbon... 

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