Q17 P. - Organic Chemistry (Mcmurry)

Question

Using curved arrows, show how the species in part (a) can act as Lewis bases in their reactions with HCl, and show how the species in part (b) can act as Lewis acids in their reaction with ${\mathbf{OH}}^{\mathbf{-}}$.

(a) ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{OH}\mathbf{,}\mathbf{HN}{\left({\mathbf{CH}}_{\mathbf{3}}\right)}_{\mathbf{2}}\mathbf{,}\mathbf{P}{\left({\mathbf{CH}}_{\mathbf{3}}\right)}_{\mathbf{3}}$ (b) ${\mathbf{H}}_{\mathbf{3}}{\mathbf{C}}^{\mathbf{+}}\mathbf{,}\mathbf{B}{\mathbf{\left(}\mathbf{CH}\mathbf{\right)}}_{\mathbf{3}}\mathbf{,}{\mathbf{MgBr}}_{\mathbf{2}}$

Step-by-Step Solution

Answer

(a)

(b)

Lewis acid and bases

Lewis acid and bases are defined by the Lewis theory of acid and base reaction as electron pair acceptor and electron pair donor respectively. Therefore a Lewis base can donate a pair of electrons to a Lewis acid to form a product containing covalent bond.

${\mathrm{A}}^{+} + {\mathrm{B}}^{-} \to \mathrm{A}-\mathrm{B}$

Lewis    Lewis      Coordinate     

Acid      Base      Covalent bond

 (Electron acceptor)(Electron donor)

(a) can act as Lewis bases in their reactions with HCl

Locate the electrons pairs of the Lewis base and draw the curved arrow from the electron pair to the Lewis acid. The electron pair moves from the atom at the tail of the arrow (Lewis base) to the atom at the point of the arrow (Lewis acid). 

(b) can act as Lewis acids in their reaction with OH -

Locate the electrons pairs of the Lewis base and draw the curved arrow from the electron pair to the Lewis acid. The electron pair moves from the atom at the tail of the arrow (Lewis base) to the atom at the point of the arrow (Lewis acid).