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

Original post by ranz

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guys whats ur approach to this qs, how would i know not to draw one straight chain like i drew, this qs confused me

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I did this. The 1st one is just copy and paste of the top thing, the second is much harder, I hate drawing cyclic. TBH, I'd accept that as empty/do it last. I rather miss 1 or 2 marks and get the paper done with precision than waste time on it. These ones are made for the best candidates. I am aiming for like A lower end or high B.

Reply 1042

Original post by ranz

guys whats ur approach to this qs, how would i know not to draw one straight chain like i drew, this qs confused me

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For m/z= 129
The nh2 group and -cooh group on the same compound react together to Form a cyclic structure with an amide bond.

For m/z = 258
258/2 = 2
So that means 2 of that compound has reacted together forming another cyclic structure with the nh2 of one compound creating an amide bond with cooh of the other and vice versa. There's 2 different ways to join the 2 compounds. Either is credited.

Reply 1043

lai812matthew

Original post by ranz

guys whats ur approach to this qs, how would i know not to draw one straight chain like i drew, this qs confused me

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when you calculate the m/r of the polyglumatic acid you got 129, so you would just wrap the entire thing out to get the left image. 258/129=2, so you would just wrap 2 polyglumatic acid up to form a 10 side polygon lol.

Reply 1044

Original post by ReTakingF324/5

What question is this?

All I know for Tollens is it's a redox. You add it to Aldehyde or Ketone and if it is Aldehyde a silver mirror/ppt forms if not, then no OBSERVATIONAL change- I am sure writing no change/reaction maybe wrong cause something changes but you can't see.

I don't remember anything about conditions for tollens.

There's no specific question. I'm just talking about it generally. Thanks anyway

Reply 1045

always wondered this, in the nucleophilic mechanisms does the curly arrow go from the lone pairs or the negative charge?
And for electrophilic mechanism does the lone pair go to the positive charge or to the atom which has the positive charge on it?

oops posted it twice

Original post by tcameron

always wondered this, in the nucleophilic mechanisms does the curly arrow go from the lone pairs or the negative charge?
And for electrophilic mechanism does the lone pair go to the positive charge or to the atom which has the positive charge on it?

Nucleophilic goes from the lone pair. Because curly arrow represents the movement of an electron pair. I'd personally put it from the electrons but u might get credited if you put it from negative charge because the electrons are giving it that negative charge.

For electrophillic I do it to the atom because the atom is gaining the electrons not the charge.

Reply 1048

ranz

5

Original post by lai812matthew

when you calculate the m/r of the polyglumatic acid you got 129, so you would just wrap the entire thing out to get the left image. 258/129=2, so you would just wrap 2 polyglumatic acid up to form a 10 side polygon lol.

but how would u know its a cylic and not just 2 joined tigether in a striaght chain?

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Reply 1049

ReTakingF324/5

Original post by tcameron

always wondered this, in the nucleophilic mechanisms does the curly arrow go from the lone pairs or the negative charge?
And for electrophilic mechanism does the lone pair go to the positive charge or to the atom which has the positive charge on it?

Lone pairs. I don't know what you mean for the 2nd part?

Reply 1050

AQA papers are so much harder. If you want to practise harder questions try them out.

Reply 1051

ranz

5

Original post by ReTakingF324/5

I did this. The 1st one is just copy and paste of the top thing, the second is much harder, I hate drawing cyclic. TBH, I'd accept that as empty/do it last. I rather miss 1 or 2 marks and get the paper done with precision than waste time on it. These ones are made for the best candidates. I am aiming for like A lower end or high B.

its crazy how this kittle qs is only worth one mark soo much time. this oaper is full of those silly one markers

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Reply 1052

Original post by ranz

but how would u know its a cylic and not just 2 joined tigether in a striaght chain?

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Draw the straight chain one and then calculate it's m/r. It wouldn't equal the values they give you

Reply 1053

Original post by ranz

but how would u know its a cylic and not just 2 joined tigether in a striaght chain?

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The fact that it says it is not a polymer and the molecular mass decreased is always an indication that the structure must be cyclic - that's what my teacher said

Reply 1054

Original post by ReTakingF324/5

Lone pairs. I don't know what you mean for the 2nd part?

like for the reaction of chlorine with benzene, does the curly arrow go to the Cl or the + next to the Cl

Reply 1055

virtualpainter

1

Original post by ranz

but how would u know its a cylic and not just 2 joined tigether in a striaght chain?

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It's probably about alpha amino acids which form diemers that are cyclic peptides so the assumption is that is must be a cyclic compound. Otherwise, if its not mentioned that it's an alpha amino acids,then it could be a straight chain.

Reply 1056

M.Branson98

Original post by tcameron

always wondered this, in the nucleophilic mechanisms does the curly arrow go from the lone pairs or the negative charge?
And for electrophilic mechanism does the lone pair go to the positive charge or to the atom which has the positive charge on it?

For nucleophilic mechanisms the curly arrow can go from the lone pair or the negative charge. The -ve charge represents the lone pair, so as long as you use one or the other I don't think it matters.
For electrophilic mechanisms the curly arrow can just go to the electrophile, it doesn't have to be the +ve charge. This is what the mark scheme says anyway.

Reply 1057

rory58824

Can someone clarify that the splitting patterns in NMR are the adjacent protons on the adjacent CARBON atom?

Reply 1058

Original post by rory58824

Can someone clarify that the splitting patterns in NMR are the adjacent protons on the adjacent CARBON atom?

Singlet = adjacent to no C bonded to a H
Doublet = adjacent to CH
Triplet = adjacent to CH2
Quartet = adjacent to CH3
Septet = adjacent to 2xCH3
whatever else you can just call multiplet
remember must only be protons which aren't in the same proton environment as the proton you're identifying so -CH2CH2- will not be split

C13 nmr does not have splitting

Reply 1059

rory58824