Questions on OC?

[simonlee]

1) In the real DAT, is there any reaction that has alkyl/hydride shift in SN1?
2) Do I need to remember the name of the reaction type(e.g. William ether synthesis)?
Thx.

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[Sprgrover]

Day by day my memory of the DAT is merging with things like my shopping list, so I'll try my best. I think I did have one question dealing with an alkyl/hydride shift. It listed the starting material and reagents and the choices provided made the answer very apparent. I don't recall having to know the name of the reaction type per se, though I did have to pick which set of reagents would be best for a W.E.S. With that said, if you know the reactions then their names should not be a problem.

 

[HBomb]

I did not have one on my exam. If it's on the exam, it'll definitely be one of the harder/trickier questions. Also, it's an implicit type of question...that is, it doesn't have to be directly asked because the carbocation will rearrange, and you'll just have to know that.

But a couple of points here:
1) From my understanding, the hydride/methyl shift is definitely in scope (though probably rare), so I'd recommend just learning it. It won't take much time to learn. Also if you do, it'll put a lot of OChem into perspective...meaning it'll make you understand OChem even better!!!

2) Because of rearrangement, there is a possibility of multiple products, though some major, some minor. For instance if you have an SN1 reaction, it'll get couple with E1 with the possibilities of rearrangement in both, so you'll have a ton of products. What I'm gettin at is that because of the possibility of multiple products, it's hard to write a test question that covers hydride/methyl shifts. That's probably why it's not asked a lot.

 

[Jess_SB]

Simonlee -

I had a question which asked 'which of the following reactants would most likely undergo a methyl shift' - and the answer was very apparent. But I saw no questions dealing with the names of certain rxns. These so-called 'brand-name' reactions are defintely good ones to know and understand though, even if you can't name them.

Good luck,
Jess

 

[Nismoboy]

'which of the following reactants would most likely undergo a methyl shift'

Can someone tell me how the mthyl hydride shift works, or is it just methyl shift and I'm confusing myself?

thanks in advance.

 

[sinned]

OK,

say you have a 1-chloro-2-methyl butane,

during a reaction with chlorine being the leaving group, the intermediate would be a primary carbocation with a positive charge on the #1 carbon. Once that happens, the methyl group on the #2 carbon will shift to the #1 carbon position, giving the #2 carbon the positive carbocation configuration, which would make it a secondary carbocation which is more stable than the original primary carbocation. Once the shift happens, the nucleophile can now attack the #2 carbon that is a secondary.

during a hydride shift, just a hydrogen shifts from the #2 carbon to the #1 carbon, giving the #2 carbon the positive charge, then a nucleophilic attack can proceed.

both are same ideas, where one is a methyl group shifts and the other is a hydride shifting...

also, a "1,2" shift means that it is just shifting from one carbon position to the other carbon directly next to it...the numbers don't necessarily designate that the shift occurs only at the #1 carbon and the #2 carbon...

Draw the structure out and take off the chlorine leaving group and look at the carbocation intermediate and it will make sense...

 

[Nismoboy]

OK,

say you have a 1-chloro-2-methyl butane,

during a reaction with chlorine being the leaving group, the intermediate would be a primary carbocation with a positive charge on the #1 carbon. Once that happens, the methyl group on the #2 carbon will shift to the #1 carbon position, giving the #2 carbon the positive carbocation configuration, which would make it a secondary carbocation which is more stable than the original primary carbocation. Once the shift happens, the nucleophile can now attack the #2 carbon that is a secondary.

during a hydride shift, just a hydrogen shifts from the #2 carbon to the #1 carbon, giving the #2 carbon the positive charge, then a nucleophilic attack can proceed.

both are same ideas, where one is a methyl group shifts and the other is a hydride shifting...

also, a "1,2" shift means that it is just shifting from one carbon position to the other carbon directly next to it...the numbers don't necessarily designate that the shift occurs only at the #1 carbon and the #2 carbon...

Draw the structure out and take off the chlorine leaving group and look at the carbocation intermediate and it will make sense...

Thanks a lot sinned, that just clarified it all.

 

[sinned]

OT but, do you happen to have a 350Z?

 

[Nismoboy]

OT but, do you happen to have a 350Z?

LOL, no I wish, but I do have a 01 Sentra SE

 

[Dr. Steve Brule]

LOL, no I wish, but I do have a 01 Sentra SE

hey aren't u a member of b15sentra.net? i think i've seen ur name on there

 

[Nismoboy]

Yes, actually I am, and I sport the same forum name. what's your forum name? It's pretty cool to see another person with the same interests. so do you have a se-r or spec-v? what color? have you seen the new Syndicate Kustomz CF lip kit...nice huh? Well, after asking all of these questions, I just remembered I shouldn't be talking about stuff like this, but rather stick to the subject at hand...the DAT. So are you ready for your DAT on 8/5 yet? I can't wait until it's over...mine is on 8/16.

see you at b15sentra.net

 

[Dr. Steve Brule]

i've just got the regular se-r..it's on 02 vibrant blue with a slushbox tranny..my name on here is the same as on b15 board..to tell u the truth i haven't been visiting it very much since i started studying for the DAT..so i havent' even seen the lip kit! i'll catch up on all the missed posts once i take the DAT..and to answer ur question i sure as hell hope im ready cuz i really don't want to take it again! i'll post my scores if they're not too horrible..good luck man!

 

[Nismoboy]

goodluck to you too...