razblo

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I have two questions regarding the DAT Destroyer Road Maps (and neither of them are where are the road maps located :p).

1. Referring to bromination from road map #2 and #3.

On road map #2, A benzene ring with a methyl group attached (Toluene) reacts with the reagents Br2, hv and a bromine attaches to the methyl group making a benzene with a CH2Br group (primary halide). On road map #3 a cyclopentane with a methyl group attached reacts with the same reagents (Br2, hv) but this time the bromine is attached directly to the ring at the same position as the methyl group (tertiary halide).

Is there some kind of steric hindrance or something that prevents the bromine from attaching directly to the benzene ring?

2. The other question is how similar are the reagents that are used in the Destroyer Road Maps to those that are used on the DAT?

I'm familiar with most of the reagents/reactions from my organic chemistry class but a fair number of them seem different than the ones the teacher used on tests and in-class.
 
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alanan84

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I'll take a crack at it.

I'd say that the reason the Br substitutes with an H from the methyl group is because it can't in the benzene ring. There's no H attached to the carbon where the methyl group comes off. Do you see what I mean? Whereas with the cyclopentane, the tertiary carbon that is part of the ring also has a H (because there are no double bonds) so the Br wants to go there...

As far as your second question goes, I'd also like to hear some input there. Especially as far as the Sn1, Sn2, E1, E2 reagents go... Are they similar to the reagents used in destroyer or do you get some weird nucleophiles?
 
May 22, 2009
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I have two questions regarding the DAT Destroyer Road Maps (and neither of them are where are the road maps located :p).

1. Referring to bromination from road map #2 and #3.

On road map #2, A benzene ring with a methyl group attached (Toluene) reacts with the reagents Br2, hv and a bromine attaches to the methyl group making a benzene with a CH2Br group (primary halide). On road map #3 a cyclopentane with a methyl group attached reacts with the same reagents (Br2, hv) but this time the bromine is attached directly to the ring at the same position as the methyl group (tertiary halide).

Is there some kind of steric hindrance or something that prevents the bromine from attaching directly to the benzene ring?
Don't know about your second question, but for this one: You have to remember that for radical bromination, you have to use light, peroxide, etc to initiate formation of radicals. Bromine radicals are selective and will attach preferably to tertiary>sec>prim>methyl, but you also have to remember that alkenes don't undergo radical halogenation (I think because the vinylic radical is not stable). So in the first case, the primary methyl is ur only choice for radical bromination. Where as in methylcyclopentane, you have a tertiary carbon which will be selected for instead of the primary methyl group.
If you were to do electrophilic aromatic substitution, you would have a lewis acid catalyst like FeBr3, in which case you will have a Br added to the benzene ring (the position would depend on the other groups attached, with a methyl group attached, the Br would attach ortho/para since methyl is activating).