Chapter 6, Problem 6.1P

Interpretation Introduction

Interpretation:

The curved arrow notation is to be drawn for the proton transfer between ammonia ${\text{(NH}}_{\text{3}}\text{)}$ and water, where water acts as the acid and ammonia acts as the base.

Concept introduction:

In a proton transfer reaction, a proton is transferred from a Bronsted–Lowry acid (proton donor) to a Bronsted–Lowry base (proton acceptor) in a single elementary step in which one bond is broken and another is formed simultaneously. The conjugate acid is the species that the base becomes after gaining a proton, and the conjugate base is the species that the acid becomes after losing a proton. The curved arrow notation shows the movement of valence electrons, not atoms. Each double-barbed curved arrow shows the movement of two valence electrons. To represent bond breaking, the tail of the arrow originates from the center of a bond whereas to represent bond formation, the head of the arrow points to an atom that forms the new bond, that is, $\text{σ}$ bond or the region where the bond is formed if the new bond is a $\text{π}$ bond.

Answer to Problem 6.1P

The curved arrow notation for the proton transfer between ammonia ${\text{(NH}}_{\text{3}}\text{)}$ and water, where water acts as the acid and ammonia acts as the base is drawn as follows:

Explanation of Solution

The given proton transfer reaction is between ammonia ${\text{(NH}}_{\text{3}}\text{)}$ and water, where water acts as the acid and ammonia acts as the base. As water acts as the acid, it is a proton donor and ammonia acts as the base which is a proton acceptor. The reaction would be as shown below:

The bond breaking and bond formation involves only valence electrons, so first, we need to draw all valence electrons in the given two reactants. From this, it is clearly seen which electrons are involved in the reaction, both from the reactants and from the products as shown below:

The appropriate movement of these valence electrons is shown by using curved arrow notations. One curved arrow is to be drawn from the lone pair on N to the H on water to illustrate the formation of $\text{H-N}$ bond. A second curved arrow originates from the center of the $\text{O-H}$ bond to illustrate the breaking of that bond, and points to the O atom, showing that those electrons end up as a lone pair on O. Therefore, the curved arrow notation for the proton transfer between ammonia ${\text{(NH}}_{\text{3}}\text{)}$ and water is as follows:

Conclusion

The curved arrow notation for the proton transfer of the given reaction is drawn on the basis of movement of valence electrons involved in bond breaking and bond formation.