= Solution
\b[The primary chloride undergoes an <SN2 reaction>; the triphenylmethyl chloride undergoes an <SN1 reaction>.] The primary site is accessible to back-side attack, whereas three phenyl groups make back-side attack at the triphenylmethyl site extremely hindered and stabilize its <carbocation> through <resonance>.
For the <SN2 reaction>, a suitable <transition state> is
$$
\left[\mathrm{N\equiv C\;\cdots\;CH_2(CH_2)_3CH_3\;\cdots\;Cl}\right]^{\ddagger-},
\qquad \boxed{v=k_2[\mathrm{CH_3(CH_2)_4Cl}][\mathrm{CN^-}]}.
$$
The entering C and leaving Cl lie on opposite sides of the reacting carbon, with partial C–C and C–Cl bonds. The total charge is $-1$. This <transition state> is not a discrete <reaction intermediate>.
For the <SN1 reaction>, the approximately planar $\mathrm{Ph_3C^+}$ <carbocation> is a genuine <reaction intermediate>. Assuming its formation by C–Cl <heterolysis> is rate determining and trapping is rapid,
$$
\boxed{v=k_1[\mathrm{Ph_3CCl}]}.
$$
Thus the limiting <rate law> is independent of <ethanol> <concentration>. The successive attack and <proton transfer> occur after the slow ionization; a cation-stabilizing environment and efficient trapping underpin this idealized <SN1> description.
Back to article page
