In this example, in part(a) the green atom collides with the brown diatomic molecule and forms the bound triatomic(b). Alternatively, in(c)and(d), a pink atom collides with a green diatomic to break the bond between the two green atoms and form a new bond between the pink and green atoms. Both such reactions are termed bi-molecular because the basic step in which the reaction takes place requires a collision between to independent species(i.e, the atom and the diatomic) A simple example of a unimolecular chemical reaction is offered by the arginine molecule considered above. In the first structure shown for arginine, the carboxylic acid group retains its HOOC-bonding. However, in the zwitterion structure of this same molecule, shown in Fig. 5.4, the HOOC- group has been deprotonated to produce a carboxy late anion group-Coo, with the H ion now bonded to the terminal imine group, thus converting it to an amino group and placing the net positive charge on the adjacer carbon atom The unimolecular tautomerization reaction in which the two forms of arginine are interconverted involves breaking an O-H bond, forming a N-H bond, and changing a carbon-nitrogen double bond into a carbon-nitrogen single bond. In such a process, the electronic structure is significantly altered, and, as a result, the two isomers can display very different chemical reactivities toward other reagents. Notice that, once again, the ultimate structure of the zwitterion tautomer of arganine is determined by the valence preferences of its constitutent atoms as well as by hydrogen bonds formed among various functional groups(the carboxylate group and one amino group and one-NH10 In this example, in part (a) the green atom collides with the brown diatomic molecule and forms the bound triatomic (b). Alternatively, in (c) and (d), a pink atom collides with a green diatomic to break the bond between the two green atoms and form a new bond between the pink and green atoms. Both such reactions are termed bi-molecular because the basic step in which the reaction takes place requires a collision between to independent species (i.e., the atom and the diatomic). A simple example of a unimolecular chemical reaction is offered by the arginine molecule considered above. In the first structure shown for arginine, the carboxylic acid group retains its HOOC- bonding. However, in the zwitterion structure of this same molecule, shown in Fig. 5.4, the HOOC- group has been deprotonated to produce a carboxylate anion group –COO- , with the H+ ion now bonded to the terminal imine group, thus converting it to an amino group and placing the net positive charge on the adjacent carbon atom. The unimolecular tautomerization reaction in which the two forms of arginine are interconverted involves breaking an O-H bond, forming a N-H bond, and changing a carbon-nitrogen double bond into a carbon-nitrogen single bond. In such a process, the electronic structure is significantly altered, and, as a result, the two isomers can display very different chemical reactivities toward other reagents. Notice that, once again, the ultimate structure of the zwitterion tautomer of arganine is determined by the valence preferences of its constitutent atoms as well as by hydrogen bonds formed among various functional groups (the carboxylate group and one amino group and one –NH￾group)