Many primary amines, \(\mathrm{RNH}_{2}\), where \(\mathrm{R}\) is a carboncontaining fragment such as $\mathrm{CH}_{3}, \mathrm{CH}_{3} \mathrm{CH}_{2},$ and so on, undergo reactions where the transition state is tetrahedral. (a) Draw a hybrid orbital picture to visualize the bonding at the nitrogen in a primary amine (just use a C atom for "R"). (b) What kind of reactant with a primary amine can produce a tetrahedral intermediate?

To visualize the bonding in a primary amine molecule with a nitrogen atom, start by drawing a simple Lewis structure. The primary amine, \(\mathrm{RNH_{2}}\), consists of a nitrogen atom with two hydrogen atoms and one R carbon-containing fragment attached to it. Now, focusing specifically on the nitrogen atom, it has three bonding orbitals that form sigma bonds with the other atoms in the molecule, and one non-bonding orbital that carries the lone pair electrons. As we're considering a hybrid orbital picture, the nitrogen atom undergoes sp3 hybridization, resulting in four sp3 orbitals. Here is a representation of the hybrid orbital picture of a primary amine (using a C atom for R): ``` H | R-C-N | H ``` Three of the sp3 orbitals form sigma bonds with the three surrounding atoms (R and two hydrogen atoms), while the fourth sp3 orbital houses the lone pair electrons.

To produce a tetrahedral intermediate with a primary amine, we need to find reactants that are compatible with the lone pair on the nitrogen atom. One such type of reactant are electrophilic compounds, which have a deficiency of electrons and can accept the lone pair during a reaction to create a new bond while retaining the tetrahedral geometry. A common reactant that can produce a tetrahedral intermediate with primary amines is an acid chloride (\(\mathrm{RCOCl}\)). In this system, the lone pair on the nitrogen atom of the amine can attack the electrophilic carbon atom in the acid chloride, leading to the release of the chloride ion and the formation of a new bond between nitrogen and carbon. As a result, a tetrahedral transition state is formed, which upon further rearrangements leads to the formation of an amide as the final product. In conclusion, the bonding in a primary amine involves sp3 hybridization of the nitrogen atom, with three sigma bonds and one lone pair. To form a tetrahedral intermediate, reactants need to accept the lone pair from the nitrogen atom of the primary amine, with acid chlorides being one such example.