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Let's start with this compound |dw:1442717384228:dw| React this with 1. HBr 2. HBr, HOOH 3. Br2 4. 1. BH3/THF , 2. H2O2, OH-
|dw:1442717567012:dw| |dw:1442717707774:dw| Bromine can attack the carbocation from either side. I believe this racemic/ 50:50
Yeah definitely. Next one I guess I'll do that, it starts out with the peroxides breaking homolytically: |dw:1442720990636:dw| Now you might think the next step would be for this to react with water to reform the water as a radical, but that's wrong! It propagates forward like this: |dw:1442721136165:dw| Because of this you need really little concentration of peroxide for your reaction to propagate. Part of the proof that this mechanism is really happens is you will end up with this kind of product sometimes (Although probably not specifically for this molecule since it's pretty hindered) |dw:1442721233219:dw| that's probably the worst picture I've ever drawn but my hand is shaking because I drank too much coffee haha so I'll leave it. Anyways so you can see that this will be the opposite addition of the last one, I think they call this "Anti-Markovnikov" however you can see that as long as you can draw arrows you can figure out the mechanism and remembering this silly name is not important.
it seems in that mechanism, the bromine radical attacks the double bond to form the more stable tertiary radical, which would make sense why it attaches at the less substituted position.
Yeah, excellent! This reaction is particularly interesting I think because it is stereospecific, you will always have anti instead of syn due to the mechanism. I think that's why I love organic chemistry, it's the mechanisms when you get to the point where you can start solving the problems and can begin to reason out other plausible mechanisms through experience with things like this.
To be honest, I really love the 1-2 and 1-4 reactions where you can look at kinetic vs. thermodynamic products. If this compound was conjugated to another double bond, we'd see some more interesting stuff. :)
@Woodward i always forget the stereospecific, stereoselective, enantioselecctive, and regioselective
If I remember this enantioselective = prefers one enantiomer over another stereoselective = one stereoisomer preferred over the other. regioselective = what carbons the atoms attach themselves to stereospecific =?
Yeah I don't remember or really know any of those words either
but look, you know whatever it is, so the name doesn't really matter, you just have to look up the name in a book if you want to publish a paper or something, but if you want to synthesize something that looks this way, where the added parts are flip-flopped you've done it, which is what's important. so what if you just forgot a silly name! :D |dw:1442771548791:dw|
The concepts are all contained in a little understanding and pushing electrons around with arrows! It's like the 'math' of organic chemistry if that's a safe comparison to make. So similarly I can say "Oh that number that means the amount of stuff you can cram into a box with side lengths l, w, h" sure, you have forgotten it's called "volume" but you knew l*w*h intuitively so it all falls into place... Of course this is just my way of thinking about it, I'm not like the end all be all, you can say you don't like it! But it's worked for me so I'm just offering it as best as I can and maybe this way of thinking about organic chemistry will help in some way. :D
I see thanks for the insight @Woodward
last one though
I believe these are two separate steps |dw:1442774302979:dw|
The step with the peroxides, and the hydroxyl group, i think those mechanism resemble a radical mechanism. i'm pretty sure it's the reaction with the borohydride first, then you use H2O2 and OH-
Yeah this is not a mechanism you can understand quickly or all at once, it's quite involved in that it's based on a quirky thing about Borane. The thing is, this is one of the few times you'll see a Hydrogen atom more electronegative than another atom. So what it does is it adds antimarkovnikov in a concerted reaction all at once. |dw:1442775092227:dw| So imagine it coming in like this with the plane of BH3 over the plane of the double bond, like one hand over the other, about to clap. Then the reaction shifts the double bonds around all at once, so then you just end up with this: |dw:1442775225689:dw| The next step with peroxide will then go through some tricky steps that I don't quite remember that retains stereochemistry and the BH2 group will shuffle around a bit and be turned into an OH group. Overall this reaction has the effect of giving you an antimarkovnikov alcohol group and a hydrogen atom syn to each other, which just means they added on the same face as opposed to the other way. I'm sure you can find some mechanism on the internet of this, there are multiple great sites out there, I suggest getting Master Organic Chemistry's reagent guide, totally worth the price but at the very worst I can probably dig up the version I bought 3 or so years ago if you can't afford it or whatever.