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

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Original post by lai812matthew
1. oh nh doesn't split 2. d2o is used


i dont mean the spliting pattern, i mean the chemical shift value splitting was 2 doublet and 1 multiplet right ?
Can someone confirm, is the first answer saturated fat or the other unsaturated ones??
Original post by SlippyDuck117
Did anyone else fine that exam rather difficult? I would've much preferred a paper like last year's ...

Very few standard questions and no big nmr question too :frown: :frown: :frown:

Been getting 50-55/60 on past papers, I don't think I've got more that 40 looking back at all the mistakes I've made.


i agree and i think i got about 40 marks as well :/
Could you say that a use for polyamides is to make plastics?
Original post by Michaelj99
Does it have to have the methyl?! I just did it as straight pentanone :/


Because it is the only isomer with 4 carbon environments
Exactly!

NMR is like my specialty man, I got 6/7 on last years question because I didn't comment on the N-H peak!
At least I'm not alone in thinking this! I'm hoping for full UMS on F325, I really need it after that terrible unit 4.
Original post by anndz3007
i dont mean the spliting pattern, i mean the chemical shift value splitting was 2 doublet and 1 multiplet right ?


?yeah
For the polyamide question, was it a use of NYLON specifically or any polyamide?
Original post by selenmer
Could you say that a use for polyamides is to make plastics?


yep, nylon is a polyamide and is a plastic, so that should get you the mark :smile:
Original post by popo111
Can someone confirm, is the first answer saturated fat or the other unsaturated ones??



I wrote the one with 2 double bonds purely becuase it leads to more trans structures?
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Original post by adnan_ja01
for the equation of the reduction of the aldehyde to alcohol, would putting OH- as a second product be fine?


no
Original post by FluffyCommie
yep, nylon is a polyamide and is a plastic, so that should get you the mark :smile:


OMG THANK YOU SO MUCH :smile:)) that has made me so much happier, i know its only one mark but one mark can make all the difference
Original post by JennyMoorcroft
My friend wrote his structures in pencil, will the pencil pick up for marking?


The invigilators always say 'pencils may be used for drawings and rough notes' so I should assume so! (i go over mine in pen afterwards though bc I worry)

Original post by Spwoosh
It wouldn't be branched at all, everybody just got a little over excited and over complicated it. It's literally ch3ch2ch2ch(oh)ch3. CNMR peaks are the distance of the carbons from the electronegative point. The Ch2 next to the Ch(oh) will have the same peak as the Ch3 on the other end of the Ch(oh) so there are only 4 peaks. We were right. The answer most people got was wrong because if you look at it carefully you'd see it only has 3 peaks.


I don't think thats right? (CH3)2CHCH(OH)CH3 would give 4, not 3 peaks, as the two methyl groups are in identical environments.
Original post by faglad202
I wrote the one with 2 double bonds purely becuase it leads to more trans structures?


Yeah that's what I thought, but apparently it said that trans fats aren't naturally occuring and the fats were naturally occuring, so apparently they were cis??

I know it's only like 1 mark lol, but as the first question it bloody well did trip me!
For the first step of the incomplete mechanism question (2 marks),

I just put positive dipole on the carbon and negative dipole on the oxygen.
And a curly arrow going from the double bond to the oxygen.

Did we have to draw the OH- attacking the carbon with a curly arrow as well?
Stearic acid is the most likely to cause CHD as saturated fats cause LDLs to build up and hence bad cholesterol.

(drawing a triglycerides formed of a glycerol and three fatty acid chains + a trans fat)

Cis-trans isomerism requires different groups attached to each carbon in c=c bond.

Alcohol and amide functional groups

Condensation polymer was polyamide + used in clothing

Mention levels of adsorption leading to separation. Then measure Rf values and compare with known Rf values. 2 spots instead of 3 because compounds may not have separated fully and hence have similar Rf values etc..

Polylactic acid could breakdown because ester linkages can be hydrolysed (acid/alkali) and the C=O bond is photodegradable as absorbs IR radiation.

Percentage yield mass = 2.66g (2.6564)

2 optical isomers are made when molecule is synthesised unnaturally compared to only 1 when synthesised naturally

Formula for peak A was just molecular formula with positive charge
Peak B was CH3CH2NH2 + positive charge with m/z of 44

Rest of question on identifying the compounds

Please add to it will help everyone out xx not all will be right :smile:
Original post by cr7alwayz
For the first step of the incomplete mechanism question (2 marks),

I just put positive dipole on the carbon and negative dipole on the oxygen.
And a curly arrow going from the double bond to the oxygen.

Did we have to draw the OH- attacking the carbon with a curly arrow as well?


yeah i thought it was like a reduction except we use OH-
Original post by Spwoosh
It wouldn't be branched at all, everybody just got a little over excited and over complicated it. It's literally ch3ch2ch2ch(oh)ch3. CNMR peaks are the distance of the carbons from the electronegative point. The Ch2 next to the Ch(oh) will have the same peak as the Ch3 on the other end of the Ch(oh) so there are only 4 peaks. We were right. The answer most people got was wrong because if you look at it carefully you'd see it only has 3 peaks.


The correct answer was CH3CHOHCH(CH3)2. There was branching. fight me.
Original post by popo111
Can someone confirm, is the first answer saturated fat or the other unsaturated ones??


It is definitely saturated. The question said NATURALLY occurring fatty acids and the majority of naturally occurring ones are Cis, only becoming Trans when undergoing Dehydrogenation. Plus, there was no way to tell whether Oleic or Linoleum acid were Cis or Trans but Saturated fats definitely increase your L Cholesterol levels.

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