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Topic: What is more reactive? A double bond or an alcohol?  (Read 2270 times)

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Offline Calicum

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What is more reactive? A double bond or an alcohol?
« on: January 17, 2013, 12:00:48 AM »
Lets say I have a molecule with a double bond and an alcohol, which is more reactive with let's say HBr? I was thinking that the alcohol would react faster than the double bond, but what do you think?

Offline discodermolide

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Re: What is more reactive? A double bond or an alcohol?
« Reply #1 on: January 17, 2013, 12:42:28 AM »
You will have to be more specific about your molecule. For example, is the double bond substituted, i.e. secondary, tertiary etc? Where is it in relation to the alcohol? Is the alcohol primary, secondary….. ?
Trans double bond, cis double bond?
And so on.
If we do not know what you are talking about then we can't answer the question.
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Offline Calicum

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Re: What is more reactive? A double bond or an alcohol?
« Reply #2 on: January 17, 2013, 12:47:25 AM »
Hmm, how about something like this?

CC(C)(O)C=C

Offline discodermolide

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Re: What is more reactive? A double bond or an alcohol?
« Reply #3 on: January 17, 2013, 12:48:55 AM »
OK, what do you think?
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Offline Calicum

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Re: What is more reactive? A double bond or an alcohol?
« Reply #4 on: January 17, 2013, 12:52:42 AM »
I was thinking that the alcohol would react faster than the double bond.

Offline discodermolide

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Re: What is more reactive? A double bond or an alcohol?
« Reply #5 on: January 17, 2013, 12:54:26 AM »
That's what I think too, do you know why?
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Offline Calicum

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Re: What is more reactive? A double bond or an alcohol?
« Reply #6 on: January 17, 2013, 01:04:10 AM »
Hmm I was think that because of the electronegativity of oxygen compared to the rest of the molecule, namely the oxygen is more electron rich (bigger s- charge).

I kind of fear this is the major product:
CC(C)=CCBr

Maybe if I do it at 0o Celsius I will get this?:

CC(C)(Br)C=C


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Re: What is more reactive? A double bond or an alcohol?
« Reply #7 on: January 17, 2013, 01:11:23 AM »
If you protonate the alcohol it will leave as water, the carbocation is tertiary and can be stabilised by the C=C, so perhaps the first compound with the primary bromide will be the product.
You may have to go much lower than 0°C to start seeing temperature effects.
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