2.11 Mechanisms
Posted by: intechemistry on: September 23, 2010
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6 Responses to "2.11 Mechanisms"
May 4, 2011 at 4:59 pm
Salam.
The types of reaction you need to know can be classified as such:
1) addition (nucleophilic and electrophilic)
2) substitution (radical, Sn1, Sn2 and electrophilic)
3) elimination
4) redox
5) condensation
You also should be familiar with
Propanone + Iodine to form iodopropanone
Of these, you need to know the mechanism of 1, 2, 3, not 4, but possibly 5 (e.g. acid chloride reactions) and the mechanistic details of propanone and iodine.
You will have to tell me how you think they can be distinguished.
May 7, 2011 at 2:11 pm
Thanks sir..
At first I thought differently about ‘type of reaction’ and ‘mechanism’..
eg; nucleophilic substitution; nucleophilic is the ‘type of reaction’ and substitution is the ‘mechanism’… or electrophilic addition; electrophilic is the ‘type of reaction’ and the addition is the mechanism..
May 7, 2011 at 6:08 pm
Each type of reaction occurs by some mechanism.
The ‘reaction type’ is usually a more general classifiaction than the specific mechanism.
Various different species may be able to undero a general nucleophilic substitution, but the mechanism by way they occur can have differences between them.
Nucleophilic substitution is one type of reaction. This type can occur by an SN1 or SN2 mechanisms
May 9, 2011 at 2:55 pm
salam sir,
what’s the difference between nucleophilic substitution and nucleophilic addition-elimination?
May 9, 2011 at 5:07 pm
Salam.
I don’t think the two will be distinguished at A-level. I think it’s OK to just use the wording “nucleophilic substitution”.
If you really want to know, I’ve always thought of the subtle (slight, delicate) difference like this:
In nucleophilic substitution (a simple procedure) a nucleophile e.g. OH- attacks a molecule, e.g. R-X, and then a straightforward or simple swap happens where a single bond breaks and a new nucleophile is ejected e.g. forming X-.
In nucleophilic addition-elimination, the outgoing species doesn’t involve a straight swap of nucleophiles by having just the one “bond” break. What I mean can be demonstrated by the reaction of carbonyls with 2,4-DNP.
2,4-DNP is a nucleophile. It attacks the carbon atom in carbonyl compounds. At the end of the reaction, a H2O molecule is eliminated. That H2O wasn’t ‘lying around’ on the the carbonyl waiting to be swapped out for the incoming 2,4-DNP. A series of internal bonds had to break and ‘rearrange’ in order for the H2O (which started out as being a =O bond!) to break away.
That’s my view of it, but I don’t think there are any God given rules about which name must be applied. Most people are happy saying addition-elimination = substitution.
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May 4, 2011 at 12:40 pm
Salam sir…
How can I distinguish the difference between mechanism and type of reaction?