Nitrogen nonbonding pair

The nonbonding pair on the nitrogen atom occupies the 2 s orbital, which Is the only valence orbital of this atom not used for bonding. 

Because the breadth of chemical behavior can be bewildering in its complexity, chemists search for general ways to organize chemical reactivity patterns. Two familiar patterns are Br< )nsted acid-base (proton transfer) and oxidation-reduction (electron transfer) reactions. A related pattern of reactivity can be viewed as the donation of a pair of electrons to form a new bond. One example is the reaction between gaseous ammonia and trimethyl boron, in which the ammonia molecule uses its nonbonding pair of electrons to form a bond between nitrogen and boron ... 

Ammonia is a prime example of a Lewis base. In addition to its three N—H bonds, this molecule has a lone pair of electrons on its nitrogen atom, as Figure 21-1 shows. Although all of the valence orbitals of the nitrogen atom in NH3 are occupied, the nonbonding pair can form a fourth covalent bond with a bonding partner that has a vacant valence orbital available. 

FIGURE 5.16 The electron dot structure of a nitrogen atom (left) and an ammonia molecule (right). The pair of electrons above the nitrogen is the nonbonding pair available for coordinate covalent bonding. 

Both the trans conformation 192 and one of the cis conformations 193 are destabilized by a nonbonded interaction between C-l-H and C-(ll)-H, whereas 192 and 194 are possibly destabilized by an interaction between the nitrogen lone pair and the 7t-electron system of the benzene ring. [A... 

Attack at C-3 gives a carbocation that is resonance-stabilized by a nonbonded pair of electrons on the adjacent nitrogen. Attack at C-2 gives a cation in which the positive charge is not adjacent to an atom bearing nonbonded electrons. Any additional resonance contributors disrupt the benzenoid structure in the left ring. Therefore, electrophilic aromatic substitution reactions of indole occur primarily at C-3. 

Conventional hydrogen bonds are formed between a proton donor, such as an O-H or N-H group and a proton acceptor, such as oxygen or nitrogen lone pair. In all such cases a nonbonding electron pair acts as the weak base component. 

The electrons in the o and G MOs formed from the 2s MOs also cancel out—these electrons effectively sit on the atoms, two on each, and form lone pairs—nonbonding pairs of electrons that do not contribute to bonding. All the bonding is done with the remaining six electrons. They fit neatly into a o bond from two of the p orbitals and two Jt bonds from the other two pairs. Nitrogen has a triple bonded structure. 

Amine (Sections 21.11, 25.1) A basic organic nitrogen compound having the general structure RNH2, R2NH, or R3N. An amine has a nonbonded pair of electrons on the nitrogen atom. 

Conceivably, the azo-ir system of II could be derived from the internal redox reaction implied in the elimination-addition sequence depicted in the production of III. Subsequent /3 elimination would afford the desired double bond. In the case of nitrogen as the neighboring atom the ylide intermediate of Scheme 26.1 would not be necessary since the availability of a nonbonding pair of electrons should make the use of base accessory. Thus the reaction pathway would be subsequently shortened. Moreover, the required electrophile, thionyl chloride, would be present in the reaction medium in large quantity. The prospect of a Pummerer-type rearrangement during the transformation of I into II is therefore likely. 

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