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

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Original post by ewjfksd
I got that too thank you :smile:


you might be missing a hydrogen there?
Original post by anndz3007
OHCH2CH2CH2(NH)CH2CH2CH2OH i think, cus if you do NH2, N would be positive no ?, im freaking out cus i did it with NH but still put + on the N, i remembered me erased it, but i got some kind of deja vu that i put + sign back on again


nah it would have + if it was NH2 the plus is only present when there is 4 bonds to the nitrogen
Original post by ShannonD_1697
What do people think the boundaries will be for a grade C?
Also can anyone explain how they worked out the percentage yield question?

Hopefully low, the going rates on the last papers seems to be around 35 but there's split opinions on whether this was hard or not. I'm hoping the boundaries 32 hot my sake 😂😭
Original post by lai812matthew
it would produce two stereoisomer yes but why would you know is guaranteed racemic, plus racemic mixture wasn't even in the spec


Chemically-synthesised compounds will almost always produce equal amounts of both isomers. Since there was only 1 chiral centre (the one bonded to the OH, H, COOH and CH3 group), you have 2 different enantiomers.

From Wikipedia: "In chemical synthesis of enantiomeric substances, non-enantiomeric precursors inevitably produce racemic mixtures"

From the spec:
"(d) explain that molecules prepared synthetically inthe laboratory often contain a mixture of opticalisomers, whereas molecules of the samecompound produced naturally by enzymes inliving systems will often be present as one opticalisomer only;"

I don't think you have to use the word racemic to get the mark, but certainly you're expected to know the above.
Original post by Michaelj99
ohh **** there were 4 C environments ;-; fml man hopefully i get ecf


yh hopefully! they're always pretty good with ecf and you'll make up the marks elsewhere!
Original post by wer34576
haha for the question on what purpose would the polymer be used for i put as a "fibre like nylon" not even realising it was nylon :facepalm:


I didn't know it was nylon, to be fair. I just put fibres in clothing xD
Original post by 1z3
For the fragment ions and molecular ion, how were you supposed to show the + charge? For the fragment ion I put a + charge near the carbon where the bond broke and for the molecular ion I just put a + charge next to the molecule structure. Should I have used brackets?



Me too
did the tripeptide have 3 chiral carbons? I deffo know 2 of the AAs where glycine and aspartamic acid

the 3rd AA was isolueine right?
Original post by drandy76
I think 2/3 marks for finding the carboxylic acid 4/5 marks for the diagrams each, so possibly 4/5 out of 7 imo


Posted from TSR Mobile


Actually i take it back. Your reasoning sounds more sensible.
I didn't even realise the whole 4 C thing, yet I still managed to get the right answer somehow.
Original post by anndz3007
check the book page 95, the 2 NMR with and without D2O, the only thing that changed is the presence of the O peak


I'm talking about the chemical sift. And Splitting. Lets move on, doesn't change anything really :smile:
GRADE BOUNDARIES
54 - A*
46 - A
42- B
38 - C

https://6f67e399b143b12f3bec4fff3bff9d8b9ac112d6.googledrive.com/host/0B1ZiqBksUHNYMDVPQWh4Y04tbkk/Grade%20Boundaries%20-%20OCR%20Chemistry%20A%20A2.pdf
(edited 7 years ago)
So what was the correct answer fir that q asking the difference between the fermentation and chital synthesis?
Original post by selenmer
So what was the correct answer fir that q asking the difference between the fermentation and chital synthesis?


(d) explain that molecules prepared synthetically inthe laboratory often contain a mixture of opticalisomers, whereas molecules of the samecompound produced naturally by enzymes inliving systems will often be present as one opticalisomer only;
Original post by 24u5owehjr34uoer
did the tripeptide have 3 chiral carbons? I deffo know 2 of the AAs where glycine and aspartamic acid

the 3rd AA was isolueine right?


pretty sure it was 3. 2 from the non glycine amino acids and 1 on the third amino acids side chain(think this is the 3rd amino acid in the table-cant remember name though).

actualy i can remember the side chain(R) had a h a CH3 and a CH2CH3
(edited 7 years ago)
Someone have a clue what the grade boundaries will be for A/A*? feel like it'll be 52/51 for an A*, 48/47 for an A... im guessing this off of jan 2013, it was one of those that had a mix of easy and hard questions, grade boundary was high for that paper
Original post by wer34576
haha for the question on what purpose would the polymer be used for i put as a "fibre like nylon" not even realising it was nylon :facepalm:


oh man i did that as well!! why didnt i read the question :frown:
For the impurity, I had 2 propanols joined by their second carbon to an NH, linking them, does that seem right?
Also for the first q i wrote saturated but i just wrote that it could pack more closely together and i didnt write anything ti do with raising ldl or cholesterol, do you think id still get the mark?
Original post by wer34576
pretty sure it was 3. 2 from the non glycine amino acids and 1 on the third amino acids side chain(think this is the 3rd amino acid in the table-cant remember name though).


This is correct, it was isoleucine. The carbon bonded to the CH2CH3, H, CH3 and the rest of the tripeptide.

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