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How to determine whether a reaction is an SN1 or SN2 reaction? I am unable to determine whether a reaction would form a transition state or not, I referred the NCERT textbook but didn't found anything that could clear my doubt.

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  • $\begingroup$ I would like to suggest this book: Electron Flow in Organic Chemistry by Paul H. Scudder. Helped me a lot! $\endgroup$ Jun 14, 2017 at 17:50

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SN1 is characterized by the possibility of formation of a stable carbocation during the reaction, whereas in the case of SN2 there cannot be formed a stable carbocation, so the most stable "intermediate" structure would be a transitional state. Stable carbocations are formed via groups with strong inductive electronic effects (+I those that repell electrons) or they can be stabilized by conjugation (the case for this one is when you have a double, triple bond or an aromatic ring directly bound to the carbon atom where the substitution takes place) so, for example, (CH3)3C-Cl would make for an SN1 when reactiong with alcohols. Also compounds like CH2=CH-CH2-Cl. The remaining cases, for example CH3-Cl or CH3-CH2-Cl would work via SN2, because the carbocation cannot be stabilized. Hope that's gonna help you :)

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  • $\begingroup$ Sn2 will form a transition state and Sn1 will form an intermediate product. $\endgroup$ Jun 14, 2017 at 9:42

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