A-level chemistry help!

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science_geeks
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#1
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#1
Hi everyone,

I'm a little bit confused with the difference between an electron withdrawing group and an electron attracting group? I understand the positive inductive effect in terms of amines and how the electrons are being pushed into the N atom from the alkyl groups but, I don't generally seem to understand electron withdrawing and electron attracting.

Please can someone help explain this.

Thanks in advance
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BTAnonymous
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#2
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#2
It's literally the opposite. Aryl groups (benzene rings) will withdraw electrons in the structure of a molecule. So if you had phenylamine, this would be a weaker base than methylamine because the phenyl group draws the electrons on the nitrogen closer to itself , whereas the methyl group 'pushes' the electrons even further onto the nitrogen. Hence, the nitrogen atom on the phenyl molecule will be less available to accept protons thus is a weaker base than the methylamine.

That's the extent of my knowledge anyway from A Level.
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science_geeks
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#3
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#3
(Original post by BTAnonymous)
It's literally the opposite. Aryl groups (benzene rings) will withdraw electrons in the structure of a molecule. So if you had phenylamine, this would be a weaker base than methylamine because the phenyl group draws the electrons on the nitrogen closer to itself , whereas the methyl group 'pushes' the electrons even further onto the nitrogen. Hence, the nitrogen atom on the phenyl molecule will be less available to accept protons thus is a weaker base than the methylamine.

That's the extent of my knowledge anyway from A Level.
Thanks for your explanation. It makes sense with amines and the benzene ring but, what I don't understand is how in acyl chlorides and acid anhydrides the 'Z' group (the extra bit attached onto C=O from R-C=O) are electron withdrawing.
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BTAnonymous
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#4
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#4
(Original post by science_geeks)
Thanks for your explanation. It makes sense with amines and the benzene ring but, what I don't understand is how in acyl chlorides and acid anhydrides the 'Z' group (the extra bit attached onto C=O from R-C=O) are electron withdrawing.
Chlorine is extremely electronegative. That area surrounding fluorine in the periodic table is very electronegative (F is the most electronegative element I think and forms the strongest organic bond; C-F) so they will not only draw electrons towards themselves in covalent bonds, but also in the whole organic structure.

So you can imagine, if you have that acyl chloride group and then along the chain is an amine group, the amine will not be a very good base because the chlorine will withdraw those electrons on the amine group, towards itself!
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science_geeks
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#5
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#5
(Original post by BTAnonymous)
Chlorine is extremely electronegative. That area surrounding fluorine in the periodic table is very electronegative (F is the most electronegative element I think and forms the strongest organic bond; C-F) so they will not only draw electrons towards themselves in covalent bonds, but also in the whole organic structure.

So you can imagine, if you have that acyl chloride group and then along the chain is an amine group, the amine will not be a very good base because the chlorine will withdraw those electrons on the amine group, towards itself!
So, I now understand how the acyl chloride is electron withdrawing but why the acid anhydride? But, there doesn't necessarily have to be amine group along the acyl chloride - will it still be electron withdrawing due to the electronegative chlorine? But if chlorine pulls electrons towards itself due to the electronegative nature of it how does that make the whole molecule electron withdrawing?

Sorry, for the questions I'm still quite confused :confused:
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BTAnonymous
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#6
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#6
(Original post by science_geeks)
So, I now understand how the acyl chloride is electron withdrawing but why the acid anhydride? But, there doesn't necessarily have to be amine group along the acyl chloride - will it still be electron withdrawing due to the electronegative chlorine? But if chlorine pulls electrons towards itself due to the electronegative nature of it how does that make the whole molecule electron withdrawing?

Sorry, for the questions I'm still quite confused :confused:
Well I guess acid anhydrides have many oxygen atoms which are also quite electronegative compared to carbon so they will also withdraw electrons just like the chlorine atom on acyl chlorides.

Unfortunately at this level (because I'm doing in A2 so I don't have an answer to that) you just need to accept that the electronegativity will have an effect on the whole molecule. I'm sure there's an explanation on the internet but it could be very complex.

Don't be afraid of asking questions, it's how I and most people learn
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science_geeks
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#7
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#7
(Original post by BTAnonymous)
Well I guess acid anhydrides have many oxygen atoms which are also quite electronegative compared to carbon so they will also withdraw electrons just like the chlorine atom on acyl chlorides.

Unfortunately at this level (because I'm doing in A2 so I don't have an answer to that) you just need to accept that the electronegativity will have an effect on the whole molecule. I'm sure there's an explanation on the internet but it could be very complex.

Don't be afraid of asking questions, it's how I and most people learn
Ah, I see! Of course, oxygen are also quite electronegative so they'd obviously pull electrons towards them therefore, making the whole molecule electron withdrawing! That's really no problem at all! I'm doing A2 chem too (might have guessed by the questions!) Which exam board are you?

Thank you for the help, finally got there in the end! I couldn't agree more, I just don't want to sound like a nuisance especially when I don't understand the first or second time. But, thanks for not giving up!
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BTAnonymous
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#8
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(Original post by science_geeks)
Ah, I see! Of course, oxygen are also quite electronegative so they'd obviously pull electrons towards them therefore, making the whole molecule electron withdrawing! That's really no problem at all! I'm doing A2 chem too (might have guessed by the questions!) Which exam board are you?

Thank you for the help, finally got there in the end! I couldn't agree more, I just don't want to sound like a nuisance especially when I don't understand the first or second time. But, thanks for not giving up!
Woooo! It's my pleasure

I'm doing AQA and first exam is in 3 weeks!
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science_geeks
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#9
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#9
(Original post by BTAnonymous)
Woooo! It's my pleasure

I'm doing AQA and first exam is in 3 weeks!
Ah! I know, I'm doing AQA too. Hope the revision is going well
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BTAnonymous
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(Original post by science_geeks)
Ah! I know, I'm doing AQA too. Hope the revision is going well
Aye it is thanks! What topics are you worried about most (don't mean to be stressful or anything lol)? I'm really dreading transition metals and their reactions... ugh, they annoy me a lot.
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science_geeks
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#11
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(Original post by BTAnonymous)
Aye it is thanks! What topics are you worried about most (don't mean to be stressful or anything lol)? I'm really dreading transition metals and their reactions... ugh, they annoy me a lot.
Ahh, I'm not looking forward to transition metals and their reactions either! In fact, I don't like most of the inorganic especially, group 7 and period 3! But, I'm most dreading NMR I've just about got it but hope there is an easy question on it!
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BTAnonymous
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#12
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#12
(Original post by science_geeks)
Ahh, I'm not looking forward to transition metals and their reactions either! In fact, I don't like most of the inorganic especially, group 7 and period 3! But, I'm most dreading NMR I've just about got it but hope there is an easy question on it!
lmao, I hate NMR as well. Everytime I do a past paper and there's an NMR question, I just go "NOPE!" and leave it till the end. I really need to brush up on it lol.

And period 3 reactions are quite horrible as well. You either know it or you don't...
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science_geeks
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#13
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#13
(Original post by BTAnonymous)
lmao, I hate NMR as well. Everytime I do a past paper and there's an NMR question, I just go "NOPE!" and leave it till the end. I really need to brush up on it lol.

And period 3 reactions are quite horrible as well. You either know it or you don't...
Lol, I've just been avoiding the topic altogether! But, I'll have to revise it at some point!

Exactly! I prefer the bits of chemistry where you can just work things out (like, some mechanisms) instead of having to rote learn stuff.
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BTAnonymous
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#14
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(Original post by science_geeks)
Lol, I've just been avoiding the topic altogether! But, I'll have to revise it at some point!

Exactly! I prefer the bits of chemistry where you can just work things out (like, some mechanisms) instead of having to rote learn stuff.
Yeah, that's what I don't like about chemistry sometimes which is probably why I hate transition metals. It feels a lot more satisfying as well if you know what I mean when you work things out which aren't exactly on the spec but you've worked it all out yourself.
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science_geeks
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#15
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#15
(Original post by BTAnonymous)
Yeah, that's what I don't like about chemistry sometimes which is probably why I hate transition metals. It feels a lot more satisfying as well if you know what I mean when you work things out which aren't exactly on the spec but you've worked it all out yourself.
Yeah, I completely understand what you mean. I just wish all of chemistry was like that!
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BTAnonymous
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(Original post by science_geeks)
Yeah, I completely understand what you mean. I just wish all of chemistry was like that!
baa, just can't wait to finish these exams and to be a free soul for a few months!!!
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science_geeks
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#17
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(Original post by BTAnonymous)
baa, just can't wait to finish these exams and to be a free soul for a few months!!!
I know! I do though sometimes feel I could work a bit harder y'know? It's like enough isn't enough. How many hours of revision do you do? I tried using a revision timetable but it didn't quite work out - do you use one?

I always get naming N-sub'd amides wrong, do you have a way of remembering how to name them?
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BTAnonymous
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#18
(Original post by science_geeks)
I know! I do though sometimes feel I could work a bit harder y'know? It's like enough isn't enough. How many hours of revision do you do? I tried using a revision timetable but it didn't quite work out - do you use one?

I always get naming N-sub'd amides wrong, do you have a way of remembering how to name them?
Yeah, sometimes I just don't feel satisfied with my understanding feel almost guilty. I left my revision late tbh and have steam rolled for the past 4 weeks. I'd say I've averaged 6 hours a day, some days more, some days less. I used a revision because I was really worried I wouldn't fit everything in. I have covered most topics I was unsure of and it's just about fixing up the topics I'm still bad at while still doing past papers.

N amides, I just remember them being in alphabetical order with them using the -yl suffix.

I really recommend this Youtuber (if you don't already): https://www.youtube.com/channel/UCps...su6-b-7mwK41lg

he's really concise and covers the specification very well for AQA speed the video to 1.25x if you want because some long videos can be slow
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BTAnonymous
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#19
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(Original post by science_geeks)
I know! I do though sometimes feel I could work a bit harder y'know? It's like enough isn't enough. How many hours of revision do you do? I tried using a revision timetable but it didn't quite work out - do you use one?

I always get naming N-sub'd amides wrong, do you have a way of remembering how to name them?
Another tip which is useful for chemistry is writing down the answers down on a piece of A3 on the questions you got wrong, especially if you've noticed you repeatedly get them wrong. E.g. on my sheet I have the chlorination of chlorine in the ozone reaction thing, the transition catalyst reactions and some other random definitions.

Most of the questions will be very familiar, even with the new spec, so it's a really good summary sheet to look at before the exam.
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science_geeks
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#20
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#20
(Original post by BTAnonymous)
Yeah, sometimes I just don't feel satisfied with my understanding feel almost guilty. I left my revision late tbh and have steam rolled for the past 4 weeks. I'd say I've averaged 6 hours a day, some days more, some days less. I used a revision because I was really worried I wouldn't fit everything in. I have covered most topics I was unsure of and it's just about fixing up the topics I'm still bad at while still doing past papers.

N amides, I just remember them being in alphabetical order with them using the -yl suffix.

I really recommend this Youtuber (if you don't already): https://www.youtube.com/channel/UCps...su6-b-7mwK41lg

he's really concise and covers the specification very well for AQA speed the video to 1.25x if you want because some long videos can be slow
Yeah, that's the problem I suppose if I would have had more time I would have liked to sit down and fully understand things but you just don't have the time.

Glad you've got what you wanted to go through covered! I started with the easier topics and am dreading it now to go through the harder ones now. That's a good amount of hours to touch each day, I think any more and it can get quite stressful then, the knowledge just won't go in!

Yeah, I've used E rintoul a few times but you're right he can be quite slow thanks, I'll try speed him up a bit next time!
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