Sn1/Sn2 - benzylic/allylic

[SCDP]

So for primary alkyl halides I know it is most likely going to be Sn2, but in Chad's vids he did say benzylic/allylic carbons with the halogen attached can undergo Sn1. So if you have a molecule with a benzylic/allylic carbon with a primary alkyl halide, if you have a strong nucleophile is that just Sn2, and with a weak nucleophile Sn1(despite the primary halide)???

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[DAT Destroyer]

So for primary alkyl halides I know it is most likely going to be Sn2, but in Chad's vids he did say benzylic/allylic carbons with the halogen attached can undergo Sn1. So if you have a molecule with a benzylic/allylic carbon with a primary alkyl halide, if you have a strong nucleophile is that just Sn2, and with a weak nucleophile Sn1(despite the primary halide)???

A benzylic or allylic halide can undergo either SN1 or SN2 depending on the conditions. Here is a nice guideline......If a primary benzylic/allylic reacts with a CN-. Sulfur nucleophile.. like CH3S-.....NH2-......hydroxide.... methoxide, ethoxide....do SN2...since these are strong nucleophiles and favor the SN2 process. If you see a weaker nucleophile like alcohols, water, or polar protic conditions .....do Sn1.

Lets do an example.....react benzyl chloride with Sodium cyanide,,,,,,, then in another process we react it with ethanol......we get which mechanisms ? SN2...and SN1 respectively.

Hope this helps.

Dr. Romano

 

[SCDP]

A benzylic or allylic halide can undergo either SN1 or SN2 depending on the conditions. Here is a nice guideline......If a primary benzylic/allylic reacts with a CN-. Sulfur nucleophile.. like CH3S-.....NH2-......hydroxide.... methoxide, ethoxide....do SN2...since these are strong nucleophiles and favor the SN2 process. If you see a weaker nucleophile like alcohols, water, or polar protic conditions .....do Sn1.

Lets do an example.....react benzyl chloride with Sodium cyanide,,,,,,, then in another process we react it with ethanol......we get which mechanisms ? SN2...and SN1 respectively.

Hope this helps.

Dr. Romano

Yup that does, thanks! Basically it's just the nucleophile strength that determines sn1/sn2 in those cases