OCR Chemistry A F324 Rings, Polymers and Analysis Tue 19 June 2012

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Reply 240

Pri0103

I'm really struggling to revise for this. Can't seem to get things stuck in my head :frown:

Don't know how to revise for this Unit.

Reply 241

atman7

NMR is annoying anyone got any good set of Q's for it whether it being past Q or just general ones I think thats what limits me most in this exam. Also how do you lot go about structuring your answers for an NMR question? (Proton NMR I'm talking about) And on that note anyone got any usual tips for helping with Carbon NMR I find that most difficult

Reply 242

andrew_c

Original post by freakymonkey

Yup. 57/60 for full marks (the equivalent paper in Physics is never more than 50 or so), and then 4 mark grade boundaries (49 for an A :O) down to 29/30 for an E. Ridiculous.

I blame this, not my total lack of preparation, for my C in jan :P

Oh man, im bricking it for this exam :frown:

Reply 243

kimmey

has anyone got any useful NMR resources, i think practice is just required ? :smile:

Reply 244

bencwbrown

Original post by kimmey

has anyone got any useful NMR resources, i think practice is just required ? :smile:

At the bottom of the first page to this thread, I've uploaded a booklet with past NMR questions :smile:

(the download is in the link as the booklet is too large to directly upload)

(edited 11 years ago)

Reply 245

kimmey

Original post by browb003

At the bottom of the first page to this thread, I've uploaded a booklet with past NMR questions :smile:

(the download is in the link as the booklet is too large to directly upload)

thanks pal :smile:

Reply 246

DonWorryJockIsHere

Grade boundaries where 4 marks in january. For the NMR question (I am resitting) in January I got the correct structure, drew it out, and gave it the correct name yet I still only got 8/10. So I lost 2 marks (half a grade) even when I got the correct answer, seriously WTF.

Reply 247

a5a09

Anyone who is resitting from Jan 12?

Reply 248

a5a09

Original post by DonWorryJockIsHere

I got 9/10 in that question and I got the paper back and I was sure that I did answer all the points :mad:

Reply 249

Bright

Original post by DonWorryJockIsHere

Bloody hell that is annoying! What grade did you get?

Reply 250

otrivine

how do you work out the relative peak area in NMR proton?

Reply 251

DonWorryJockIsHere

Original post by Bright

Bloody hell that is annoying! What grade did you get?

I ended getting a low B (or high C just on borderline of B) I got my paper back and there were some instances where I was careless eg a chain would have 5 carbons and it asked something like acid hydrolysis, in my products I would have a chain of 2 and another chain of 2 carbons (the chemistry was correct but just careless drawing) cost me some marks.

Reply 252

DonWorryJockIsHere

Original post by a5a09

I got 9/10 in that question and I got the paper back and I was sure that I did answer all the points :mad:

Yea it stupid I think you should get all the marks if you get the correct structure as you obviously went through all the marking points to get there even if it isnt explicitly on your paper

Reply 253

niaghez

NMR is annoying me so much! i pretty much find the rest okay its just a load of memorising but NMR is actually difficult to get a grasp of.

Reply 254

beccihayes

what mechanisms and equations do we have to learn?

Reply 255

hetty123

Original post by browb003

The safranol undergoes electrophilic addition, just like a normal alkene does. So the pi-bond of the double bond breaks, and the two bromine atoms join onto the two carbons involved in the double bond (so no hydrogens are lost).

This might help as it shows the reaction on a simple alkene (but identical principles) http://www.chemguide.co.uk/mechanisms/eladd/symbr2.html#top (you should notice that each carbon has the same number of hydrogens before and after the reaction)

thanks

does this mean that cyclic alkenes undergo electrophilic addition and arenes such as benzene undergo electrophilic substitution...is this why alkenes lose the double bond and the halogen is added and arenes just sub the hydrogen for the halogen

:rolleyes:

i think i get it!!!!!

Reply 256

Bright

Ummm I'm finding this quite difficult :/ It's A LOT of memorising to do and my brain is already saturated from F322 and F325 revision.. :/

Reply 257

niaghez

Original post by Bright

Ummm I'm finding this quite difficult :/ It's A LOT of memorising to do and my brain is already saturated from F322 and F325 revision.. :/

SAME. Im just sitting here staring at a page lol.

Reply 258

bencwbrown

Original post by hetty123

thanks

i think i get it!!!!!

Yeah that's correct :smile:

Arenes undergo electrophilic substitution rather than addition as substitution means that the delocalised ring of electrons is not permanently broken, and the delocalised ring makes benzene more stable so it would want to keep the delocalised ring

Substitution would permanently break the delocalised ring and so substitution is not energetically favourable for arenes :smile:

Reply 259

Bright