Vinyl halides (CH2=CHX) and aryl halides (PhX) do NOT undergo normal SN1 or SN2 reactions:

SN2 blocked: The electrophilic carbon is sp2 → the C-X bond is in the plane of the molecule → backside approach by nucleophile is blocked by the pi electron cloud above and below.

SN1 blocked: Vinyl cation and phenyl cation are extremely unstable (sp hybridized cation with empty orbital in the sigma framework, not stabilized by resonance).

C-X bond is STRONGER: In sp2 systems, the C-X bond has more s-character → shorter and stronger. In aryl halides, additional resonance overlap of X lone pair with ring further strengthens the bond.