Hi /sci/ I'm doing work for my organic chem 2 class and

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Anonymous
2016-01-22 05:19:50 Post No. 7801361
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Anonymous 2016-01-22 05:19:50 Post No. 7801361 [Report]

Hi /sci/

I'm doing work for my organic chem 2 class and it's been about three years since I did the first class in the series. I think I'm understanding the current material being presented but there are a couple of blanks in the middle that I think I'm missing out because lack of background knowledge.

This question is based on carbene addition to alkenes.

Two points I'd appreciate being clarified:

1. In (c), through what mechanism is there a carbene being formed to be able to attack the double bond on the cyclohexene? I'm assuming the third molecule in the equation reacts with tribromomethane to remove an H.

2. In general, the carbene attacks the double bond on the alkene to form a cyclic formation (epoxide?). When I was comparing my answers on chegg, I noticed that in (b) and (e), the carbene's carbon in the product is no longer bonded with I, while in (c), the carbene's carbon in the product *is* still bonded with the original two Br. Why is this?

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Anonymous 2016-01-22 05:21:52 Post No.7801366
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Anonymous 2016-01-22 05:21:52 Post No.7801366 [Report]

Okay, I just figured out the reasoning for question 1. I'd still appreciate input on 2 though.

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Anonymous 2016-01-22 05:25:22 Post No.7801372
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Anonymous 2016-01-22 05:25:22 Post No.7801372 [Report]

>>7801361
>In (c), through what mechanism is there a carbene being formed to be able to attack the double bond on the cyclohexene?
That's the Simmons-Smith reaction, and the mechanism generally gets ignored in undergrad organic classes b/c no one gives a fuck.

>2. In general, the carbene attacks the double bond on the alkene to form a cyclic formation (epoxide?).
Not an epoxide, but a cyclopropane.
In c) the carbene is dibromocarbene (deprotonation of bromoform followed by alpha-elimination of bromide from the anion).

In b,d,e it's a zinc carbenoid. (CH2 bound to Zn)

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Anonymous 2016-01-22 05:26:50 Post No.7801377
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Anonymous 2016-01-22 05:26:50 Post No.7801377 [Report]

>>7801372
argh I fucked up the lettering at the beginning of my reply b,d,e are all simmons smith, c is not

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Anonymous 2016-01-22 05:30:42 Post No.7801387
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Anonymous 2016-01-22 05:30:42 Post No.7801387 [Report]

>>7801372
Ah, sorry, that's right, epoxides are triangular structures with an O.

So what happens to iodine in b, d, and e?

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Anonymous 2016-01-22 05:33:27 Post No.7801392
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Anonymous 2016-01-22 05:33:27 Post No.7801392 [Report]

>>7801387

Nevermind, looked up the Simmons-Smith reaction and apparently the Zinc grabs the 2 I's.

>>7801372
Thank you for the help!