Nitrogen point

Unless otherwise noted, the phosphorus atom is placed at the origin of the reference frame, with nitrogen pointing in the positive z direction... 

The increase in the percentage of chemically linked nitrogen points to the existence of a reaction between the reactants and inorganic powder—that is, finely ground porcelain—inevitably present as a result of the balls contact with the walls of the equipment. As a matter of fact, the possibility of a mechanochemical activation of inorganic materials by vibratory milling has been reported earlier (19-21). 

Likewise, in a "3+2" acid-catalyzed condensation of N-confused tripyr-rane 140 and dipyrromethane-dicarbinol 14 (R1=R2=R3=Ar), the N-fused pentaphyrin 141 with all nitrogens pointing inward was obtained. Subsequent oxidation of 141 (Scheme 58) gave 142, which isomerized into doubly N-fused pentaphyrin 143, devoid of aromaticity (04ACI876). 

Electrostatic forces provide a generalized attraction between molecules in chemical reactions. In the reaction between chloride anions and sodium cations described above, the way in which these two spherical species approached one another was unimportant because the charges attracted one another from any angle. In most organic reactions the orbitals of the nucleophile and electrophile are directional and so the molecular orbitals of the reacting molecules exert important control. If a new. bond is to be formed as the molecules collide, the orbitals of the two species must be correctly aligned in space. In our last example, only if the sp3 orbital of the lone pair on nitrogen points directly at the empty orbital of the BF3 can bond formation take place. Other collisions will not lead to reaction. In the first frame a successful collision takes place and a bond can be formed between the orbitals. In the second frame are three examples of unsuccessful collisions where no orbital overlap is possible. There are of course many more unproductive collisions but only one productive collision. Most collisions do not lead to reaction. 

Point 2 is located on the 0.810 MPa saturated liquid curve for a concentration of 79 mol % nitrogen. Point 3 is identical with point 2 because of the throttling process. Similarly, points 4 and 5 are located on the 0.506 MPa saturated liquid curve at a concentration of 0.59 mol % nitrogen. 

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