Munrhe
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#1
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In forming Alcohols or other substitution:

Is it correct that
i) tertiary carbocation is the most stable as it has 3 alkyl groups surrounding the C-atom which has lost an electron and became a cation
ii) but the tertiary halogenoalkane which is the basis for this reaction is actually the least stable and thus most reactive?

I.e. there is both most and least stability in this structure:
i) most in terms of the cation that is surrounded by the alkyl groups and
ii) least in terms of the overall molecule that is reacting fastest? And the reason that tertiary halogenoalkanes are least stable and thus able to react so fast is due to the cation that can be formed only as it is being stabilised by the alkyl groups. So effectively, the stability and instability are kind of linked.
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username3249896
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i) "tertiary carbocation is the most stable as it has 3 alkyl groups surrounding the C-atom which has lost an electron and became a cation"
Yes

ii) "but the tertiary halogenoalkane which is the basis for this reaction is actually the least stable and thus most reactive?"
Sure, if you are considering SN1 reactions only
For SN2 reactions tertiary alkyl halides are least reactive.
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charco
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(Original post by Munrhe)
In forming Alcohols or other substitution:

Is it correct that
i) tertiary carbocation is the most stable as it has 3 alkyl groups surrounding the C-atom which has lost an electron and became a cation
ii) but the tertiary halogenoalkane which is the basis for this reaction is actually the least stable and thus most reactive?

I.e. there is both most and least stability in this structure:
i) most in terms of the cation that is surrounded by the alkyl groups and
ii) least in terms of the overall molecule that is reacting fastest? And the reason that tertiary halogenoalkanes are least stable and thus able to react so fast is due to the cation that can be formed only as it is being stabilised by the alkyl groups. So effectively, the stability and instability are kind of linked.
You are beginning to understand that there are often several factors involved in any process. This is good.

Check out this interactive on haloalkanes for a little more.
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isiaiah d
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you might not get away with just saying it has 3 alkyl groups so best to say 3 electron releasing alkyl group which stabilise the cation
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Munrhe
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(Original post by BobbJo)
i) "tertiary carbocation is the most stable as it has 3 alkyl groups surrounding the C-atom which has lost an electron and became a cation"
Yes

ii) "but the tertiary halogenoalkane which is the basis for this reaction is actually the least stable and thus most reactive?"
Sure, if you are considering SN1 reactions only
For SN2 reactions tertiary alkyl halides are least reactive.
Thank you but I thought SN1 is there only route for tertiary halogenoalkanes (or at least preferred) due to the fact that an intermediate carbonation can be formed?
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username3249896
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(Original post by Munrhe)
Thank you but I thought SN1 is there only route for tertiary halogenoalkanes (or at least preferred) due to the fact that an intermediate carbonation can be formed?
Yes this is true. SN1 is not a viable reaction route due to steric effects. Hence tertiary do not react via Sn2. [which is why I said tertiary is least reactive towards Sn2, in fact there is no reaction (or very little reaction)]
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charco
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(Original post by BobbJo)
Yes this is true. SN1 is not a viable reaction route due to steric effects. Hence tertiary do not react via Sn2. [which is why I said tertiary is least reactive towards Sn2, in fact there is no reaction (or very little reaction)]
If you look at the interactive I uploaded you will see that both mechanisms are "viable" but the rate at which they occur depends on the stucture of the haloalkane (and the solvent used).
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username3249896
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(Original post by charco)
If you look at the interactive I uploaded you will see that both mechanisms are "viable" but the rate at which they occur depends on the stucture of the haloalkane (and the solvent used).
Thank you

I used the wrong word. I agree that both are viable. I meant more along the lines of not being favoured.

Thank you
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