2011 DAT Destroyer #96 OCHEM

[pandalove89]

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Which compound reacts fastest in an SN1 type of reaction?

I thought it would be a saturated ring with a halogen because I thought aromatic halides were extremely unreactive during substitution. However, the right answer was an aromatic ring with a halogen..


Why is this? What about SN2 reactions?

 

[PooyaH]

Choice is E is not an aromatic halide! However, if you make a carbocation after kicking out the leaving group, you make an aromatic ring which is very stable!

 

[PooyaH]

Also acyl halide are very unreactive as you mentioned, BUT they would react with NH2-, substituting the halide with NH2. That'd be a very hardcore question on the DAT but it never hurts to know!

 

[pandalove89]

Also acyl halide are very unreactive as you mentioned, BUT they would react with NH2-, substituting the halide with NH2. That'd be a very hardcore question on the DAT but it never hurts to know!

Okay then how come on #180 where it has a benzene with CH2Br and I group reacting with CH3O^- and CH3OH replaces the Br on the CH2Br group instead of the I? Wouldn't it do the same thing in terms of "kicking off" the leaving group?

 

[PooyaH]

Okay then how come on #180 where it has a benzene with CH2Br and I group reacting with CH3O^- and CH3OH replaces the Br on the CH2Br group instead of the I? Wouldn't it do the same thing in terms of "kicking off" the leaving group?

A benzene is not the same thing as what choice E has on #96. Kicking off I would destabilize the aromatic benzene on #180 (which is the case with acyl halides in general). But choice E of #96 is NOT a benzene not an acyl halide and that's why kicking off Cl (halide) is possible in which it actually creates a carbocation which in turn creates an aromatic ring!

If you're still unclear on this, then I highly recommend you to start with the basics first. That way going through the Destroyer will be more effective.