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

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Reply 1960

jamesgates1

Original post by Michaelj99

thats what I did im so confused, it didn't say it was branched or anything either

Not sure.... Both structures seem to have same molecular formula though.

Reply 1961

President J

Original post by anndz3007

his/her answer was right i think, cus the middle C was attracted to N fom NH2 and the first one attract to O in OH no?/

They used D20 (or something like that) and when looking at specta, you never include Hs from N nor O

Reply 1962

anndz3007

Original post by cr7alwayz

What I remember (there may be mistakes)

octadec-9,12-enoic acid because it has two trans isomers? which increases level of bad cholesterol.

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

Alcohol and amide.functional groups

condensation polymer was polyamide and used as fibres in clothing

Measure Rf values and compare with known Rf values. 2 spots instead of 3 because compounds may not have separated fully

Polylactic acid could breakdown because ester linkages could be hydrolyses and the stitches could be dissolved because lactic acid could form hydrogen bonds with water using its OH groups.

Diester made of six carbons and two ester bonds (skeletal formula)
Percentage yield mass = 2.66g

formula for peak A was just molecular formula with positive charge
peak B was CH3CH2NH2 (or something like that) and positive charge

work out mr of Compound H Mr - 74.
Compound H: CH3CH2COOH
For Compound J: (CH3)3CH2OH

where do you put the charge on A ?? i thought nothing break down so i just leave it neutral ??

Reply 1963

arlennox

Original post by sakuraton

Got something like that except I got ethanoic acid instead of propanoic acid. 60 was the Mr

COOH Mr is 45 so there is 15 as remaining which is CH3

Am I right?

Unless I calculated the Mr wrong :frown:

Yeah the Total Mr was 74 so without cooh its 29 which is c2h5

Reply 1964

anndz3007

Original post by President J

They used D20 (or something like that) and when looking at specta, you never include Hs from N nor O

yeah you not include it but it still affect the chemical shift no ??

Reply 1965

JennyMoorcroft

My friend wrote his structures in pencil, will the pencil pick up for marking?

Reply 1966

President J

Nothing quiet like throwing away your past papers ect after an exam

Reply 1967

lai812matthew

Original post by anndz3007

his/her answer was right i think, cus the middle C was attracted to N fom NH2 and the first one attract to O in OH no?/

1. oh nh doesn't split 2. d2o is used

Reply 1968

Michaelj99

Original post by anndz3007

where do you put the charge on A ?? i thought nothing break down so i just leave it neutral ??

It's called "Molecular ion peak" and i remembered my teacher banging on about + charge so I just put the whole molecule and that whole thing has + charge

Reply 1969

FluffyCommie

Original post by swetu1

I did the same thing by putting an oh don't know if I will loose a mark and doesn't reduction involve 2H instead of 2O

It does invole [H], you're right, that was just a stupid mistake in my comment, but at least i put [H] in my exam :3

As far as i'm concerned you will probably lose the mark for putting OH-

Reply 1970

GawdHeresEmmie

Original post by FluffyCommie

Pretty sure the only acceptable form would be:

Aldehyde + 2[o] --> alcohol

2[H]**

Original post by jamesgates1

Why did the secondary alcohol and ketone have a ch3 group off it? Why couldn't it be a straight chain?

There was only 4 carbon environments on the C13 NMR spectra therefore you had to have 2 of the five C's in identical environments therefore you knew there was a CH(CH3)2

Original post by Michaelj99

thats what I did im so confused, it didn't say it was branched or anything either

Reply 1971

Spwoosh

Original post by Michaelj99

thats what I did im so confused, it didn't say it was branched or anything either

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.

Reply 1972

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:

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.

Reply 1973

username1567375

Original post by Michaelj99

thats what I did im so confused, it didn't say it was branched or anything either

if i remember correctly i think there wasn't enough carbon environments in the c nmr to be a straight chain? The number of environments was one less than the number of carbons in the compound. i could be wrong though

Reply 1974

ewjfksd

Original post by jasonx2

Anyone got 2.86g for the mass of compound A?

i got 2.86 but do you remember the questions

Reply 1975

gonecrazy

Original post by Michaelj99

Does it have to have the methyl?! I just did it as straight pentanone :/

i thought the same :s
why is the methyl needed?

Reply 1976

FluffyCommie

Original post by ewjfksd

i got 2.86 but do you remember the questions

The answer was 2.66g, not 2.86g

Reply 1977

lai812matthew

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:

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.

same

Reply 1978

cookie123456789

In my first Chemistry exam I was wearing novelty Christmas socks. They accidentally went off playing Christmas tunes. The examiner had to confiscate my socks.