Chapter 26, Problem 91IAE

Interpretation Introduction

(a)

Interpretation:

The names of functional groups present in ephedrine should be determined.

Concept introduction:

Functional groups are atom or groups of atoms which are responsible for special chemical or physical properties of the molecule. IUPAC purposed a complete list of different functional groups with their prefix and suffix which can be used in the naming of the molecule. Some of the atoms can act as functional group such as −Cl, -F, -Br etc whereas some of them are groups of atoms like −NH₂, -NO₂, -OH etc.

Interpretation Introduction

(b)

Interpretation:

Identify the hybridization of numbered C atoms and N atom in ephedrine.

Concept introduction:

Hybridization is the process of mixing of atomic orbitals to form same energy and same shape hybrid orbitals which form covalent bond with overlapping of atomic orbitals of other atoms. The number of chemical bonds formed by the atom always determines type of hybridization. Sigma bonds could only form by hybrid orbitals whereas pi bonds are always formed by overlapping of un-hybrid orbitals hence hybridization is not part of pi bond formation.

Interpretation Introduction

(c)

Interpretation:

Identify the chiral C atoms in ephedrine.

Concept introduction:

A chiral carbon atom is the carbon atom which is bonded with four different atoms or group of atoms. The presence of chiral carbon atom makes that molecule optically active so it can rotate the plane polarized light either clockwise or anti-clockwise. Such molecules are called as optically active molecule and two different configuration of same molecule are called as enantiomers. They are non-superimposable mirror images of each other.

Interpretation Introduction

(d)

Interpretation:

Calculate the pK_b value for ephedrine with the help of given information.

Concept introduction:

Ephedrine is a weak base which is mainly used as a center nervous system stimulant. Since it acts as a weak base therefore it gives OH- ions in its aqueous solution.

${\text{C}}_{\text{10}}{\text{H}}_{\text{15}}{\text{ON}}_{\text{(aq) }}{\text{+ H}}_{\text{2}}{\text{O}}_{\text{(l)}}\rightleftharpoons {\text{ C}}_{\text{10}}{\text{H}}_{\text{15}}{\text{ONH}}^{\text{+}}{}_{\text{(aq)}}{\text{ + OH}}^{\text{-}}{}_{\text{(aq)}}$

The base dissociation constant ${\text{K}}_{{}_{\text{b}}}$ for this reaction can be written as:

${\text{K}}_{\text{b}}\text{=}\frac{{\text{[C}}_{\text{10}}{\text{H}}_{\text{15}}{\text{ONH}}^{\text{+}}{}_{\text{(aq)}}{\text{] [OH}}^{\text{-}}{}_{\text{(aq)}}]}{{\text{[C}}_{\text{10}}{\text{H}}_{\text{15}}{\text{ON}}_{\text{(aq) }}]}$

The relation between ${\text{K}}_{{}_{\text{b}}}$ and ${\text{pK}}_{{}_{\text{b}}}$ is:

${\text{pK}}_{\text{b}}\text{= - log }\left[{\text{K}}_{\text{b}}\right]$