State whether each of the following $\mathrm{R}^{+}$'s is stabilized or destabilized by the attached atom or group:
(a)
<smiles>C[C](C)C(C)(C)F</smiles>
(b) $: \ddot{\mathrm{F}}_3 \mathrm{C}^{+}$
(c)
<smiles>C[C](C)N</smiles>
(d)
<smiles>C[C](C)N</smiles>
If an electron-withdrawing group is adjacent to the positive $\mathrm{C}$, it will tend to destabilize the carbocation. Electron Donating groups, on the other hand, delocalize the + charge and serve to stabilize the carbocation.
(a) Destabilized. The strongly electron-withdrawing F's place a $\delta+$ on the atom adjacent to $\mathrm{C}^{+}$:
<smiles></smiles>
(Arrows indicate withdrawn electron density.)
(b) Stabilized. Each $\mathrm{F}$ has an unshared pair of clectrons in a $p$ orbital which can be shifted to $-\stackrel{+}{\mathrm{C}}-$ via $p-p$ orbital overlap.
<smiles>CC(F)=C(C)[I+]</smiles>
(c) Stabilized. The unshared pair of electrons on $\mathrm{N}$ can be contributed to $\mathrm{C}^{+}$.
<smiles>C[CH+]=C(C)C(C)=N</smiles>
(d) Destabilized. The adjacent $\mathrm{N}$ has a + charge.