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OCR A2 CHEMISTRY F324 and F325- 14th and 22nd June 2016- OFFICIAL THREAD

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Original post by Cal 1
Ahh yes they are! My bad haha


What is it? It's not in my book?
Original post by Rust Cohle
I think people are more skeptic after F321 strayed from the spec a little.

<snip>
Oxidation of oxygen as +2 in F2O caught people out in F321 2016


I can't look at the question again because ChemistryALevel has deleted his answers, but from what I remember the all the information needed was given in the question.
Original post by tcameron
1b help please


Would it be the middle one?

Ps what paper is this?


Posted from TSR Mobile
the middle one.
make it an aldehyde and then the chiral centre is the carbon with the methyl group attactched

if they are carbonyl groups it means the only points that can be chiral centres are the ones with methyl groups. the first one doesnt have a methy group and the last one has two on one carbon so its not a chiral centre.
(edited 7 years ago)
Original post by tcameron
1b help please


Original post by Saywhatyoumean
Would it be the middle one?

Ps what paper is this?


Posted from TSR Mobile

Yeah it's the middle. Not the second as when it's ketone its bonded to two CH3 groups. Not the first as that is bonded to two H groups when ketone.
Original post by tictac198
Question on Proton Nmr. Ive realised on more than one past paper where the peak for a hydrogen bonded to a carbon attatched to a benzene cHc6h5 which has a narrow range of 2.2-2.4 has a peak higher at around 2.8. This makes it very confusing to identify as you can mistake the peak for a HC-C=O. How do you correctly identify this peak? Do you just assume it might have a higher chemical shift than given on the data sheet. Example of this on June 2012 RPA paper Q5b


Yes - as it says on the data sheet, the ranges are only typical values. As for identifying the peak, you generally have to work out the peaks that you know first. For example the cluster of splitting at 7.2 ppm is obviously caused by the protons on a benzene ring. The relative area for this peak is 5, so you know that the benzene ring has 5 protons. Now you can look at the singlet. This is in the right range for a C-H attached to a benzene ring, but if this was the environment then the relative peak area of 3 combined with the singlet means that this would be the end of the molecule and the entire structure would just be a CH3 attached to a benzene ring. This doesn't fit the information given in the question (an ester with mr = 164) so you now know to assign this peak to HC-C=O instead.

Hopefully this explanation is at least some help - although the best way to get good at NMR is to solve past questions!
Original post by Saywhatyoumean
Would it be the middle one?

Ps what paper is this?


Posted from TSR Mobile


old spec - jan 09
Original post by tictac198
Question on Proton Nmr. Ive realised on more than one past paper where the peak for a hydrogen bonded to a carbon attatched to a benzene cHc6h5 which has a narrow range of 2.2-2.4 has a peak higher at around 2.8. This makes it very confusing to identify as you can mistake the peak for a HC-C=O. How do you correctly identify this peak? Do you just assume it might have a higher chemical shift than given on the data sheet. Example of this on June 2012 RPA paper Q5b


I understand where you're coming from. Having looked at it, it's still possible to correctly ID the peak.

Since we have C6H5 the 2.2 peak can't be C6H5CH3 as it would leave no space for the ester bond. Meaning the ester link will be in between the C6H5 and CH3.
this is a really basic question but in there's 4 carbon environments for this ketone, but i can only identify 3... would the 3rd carbon count as 2 environments (c=o and c-c)? :s-smilie: EDIT: never mind, read the mark scheme wrong haha. you can tell I'm fasting.
(edited 7 years ago)
does anybody wanna skype revise?
For isoelectric points (pH at which amino acid exists as a zwitterion, the dipolar ionic form of an amino acid in which there is no overall charge as both charges present in NH3+ and COO-):

The more NH2 groups there are on the R group, the higher the isoelectric point
The more COOH groups there are on the R group, the lower the isoelectric point
I don't know what else I can do to revise, done all the pp, learned all the reactions, I really hope a proton NMR long answer question comes up and also the problems with optical isomers and how to separate them question
(edited 7 years ago)
If you're going from an aldehyde to a carboxylic acid do you still have to reflux it with acidified potassium dichromate?
there might be a zwitterion question for an amino acid with multiple groups of amine and carboxyl groups. followed by a question with low, high pH conditions for the amino acid.
(edited 7 years ago)
Original post by yoda123
I don't know what else I can do to revise, done all the pp, learned all the reactions, I really hope a proton NMR long answer question comes up and also the problems with optical isomers and how to separate them question


Same. I have no idea what else to do and when i stop I feel guilty for not working. I hope the nmr question isn't too complicated though. What are you aiming for in this exam?
Reply 1235
Avatar for ranz
ranz
5
Original post by KB_97
If you're going from an aldehyde to a carboxylic acid do you still have to reflux it with acidified potassium dichromate?


no reflux is not required, i checked earlier in the book and theres no mention, only if you go from alcohol to carboxylic acid


Posted from TSR Mobile
Original post by yoda123
I don't know what else I can do to revise, done all the pp, learned all the reactions, I really hope a proton NMR long answer question comes up and also the problems with optical isomers and how to separate them question


Skim this over a few times between between now and the exam.

https://goo.gl/nVvgw9
Reply 1237
Avatar for ranz
ranz
5
Original post by yoda123
I don't know what else I can do to revise, done all the pp, learned all the reactions, I really hope a proton NMR long answer question comes up and also the problems with optical isomers and how to separate them question


worst part is that the exam in afternoon, i just want it over and done with


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Original post by lai812matthew
there might be a zwitterion question for an amino acid with multiple groups of amine and carboxyl groups.


If the alpha amino acid has an r group that has cooh or nh2 and you're asked to draw the zwitterion, do you have to also write them as coo- / nh3+ ?
I've done Legacy papers '02-'06, OCR A papers all at least twice and a couple of Edexcel papers. Just have to think I can't have prepared any more and not stress too much :s-smilie:

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