# Why are allyl halides reactive towards both SN1 and Sn2 reactions?

I know that allyl halides are reactive towards SN1 reactions due to the stabilization of carbocation due to resonance but why are they reactive towards SN2 too?

• I actually read that allyl halides are more reactive towards SN2 than primary alkyl halides, whom I thought were most reactive. – Kirti Agrawal Feb 26 '18 at 12:01
• Can you add what you just said above to your question? – dr.drizzy Mar 4 '18 at 5:58

Keep in mind that the electronegativity order of hybridized carbons is $\ce{sp > sp2 > sp3}$. So in an allylic halide, such as $\ce{CH2=CH-CH2Br}$, the alpha carbon is much more partially positive than the alpha carbon in $\ce{CH3-CH2-CH2Br}$. Therefore, the attacking nucleophile will be attracted to the alpha carbon more in the allylic halide compound than in the primary halide. Hence, allylic halides tend to follow SN2 pathways more than primary halides.