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OCR Chemistry A F324 Rings, Polymers and Analysis Tue 19 June 2012

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Reply 80
Avatar for otrivine
otrivine
14
Original post by Fatima0065
thats erally good! whats first time? so your doing f215? and f324 and f325? and u did f322..hw r u coping?


yes i am doing F324 F325 F214 F215 all in june and its my first time doing them its so scary/stressful
Reply 81
Avatar for Oromis263
Oromis263
2
Original post by Fatima0065
oh okai..thanks anywais..would rep u but i dnt know how to lol :biggrin: what did u get for f324..hav u got any tips etc..? and is it okai if i ask for help if i need it? :smile:


I got 90, and I think the best thing I can say is when reading a question, the most important thing is to grasp what exactly it is asking you in relation to the specification. They will wrap it up in a neat little question, which may mislead you, so you've just got to focus on what is being asked.

1.

Make sure you know all your definitions

2.

Make model answers for questions which come up a lot (eg why cycloalkane < benzene < phenol in terms of bromination etc)

3.

Really get to grips with mechanisms.


Original post by Oromis263
I got 90, and I think the best thing I can say is when reading a question, the most important thing is to grasp what exactly it is asking you in relation to the specification. They will wrap it up in a neat little question, which may mislead you, so you've just got to focus on what is being asked.

1.

Make sure you know all your definitions

2.

Make model answers for questions which come up a lot (eg why cycloalkane < benzene < phenol in terms of bromination etc)

3.

Really get to grips with mechanisms.




Do you think i shoukdfirstly, go through the specification thoroughly making notes with eavch point and memorise al the mechanism in the ocr book propeerly..there's not many, there's only:
nuclophillic additon and
electrophillic substitution and basic ones but yh what do u say...and then attempt lot of question on each topic.
and finally past papers..anything else that i should do? please tell me i need ful UMS marks on this to get an A overall...:biggrin:
Original post by otrivine
yes i am doing F324 F325 F214 F215 all in june and its my first time doing them its so scary/stressful


thats crazy!! woah good luck :smile:
Reply 84
Avatar for otrivine
otrivine
14
Original post by fatima0065
thats crazy!! Woah good luck :smile:


forgot to mention c3 and c4 as well
Original post by otrivine
forgot to mention c3 and c4 as well


ur doign c4...aswel hw u finding it..its quite hard right?
Reply 86
Avatar for otrivine
otrivine
14
Original post by Fatima0065
ur doign c4...aswel hw u finding it..its quite hard right?


oh yes really hard i am having a private teacher tomorrow to help me with c4 :redface:
Reply 87
Avatar for kimmey
kimmey
7
come on guys lets not get off track talking about other subjects, keep this strictly chemistry haha

okay... what methods are there of making sure you only get one optical isomer ?

give me the equation for how D2O removes the OH group in ethanol during H NMR
Original post by kimmey
come on guys lets not get off track talking about other subjects, keep this strictly chemistry haha

okay... what methods are there of making sure you only get one optical isomer ?

give me the equation for how D2O removes the OH group in ethanol during H NMR


mehods for obtaining 1 isomer:
chiral pool synthesis
something to do woth catalysts?

and not sure bout the equation :smile:
Reply 89
Avatar for kimmey
kimmey
7
Original post by Fatima0065
mehods for obtaining 1 isomer:
chiral pool synthesis
something to do woth catalysts?

and not sure bout the equation :smile:


yep you're on the right track your first point is right, not too sure about your second, i would say use bacteria or enzymes, and chiral pool synthesis.

for the second one you have CH3CH2OH + D2O ---> CH3CH2OD + HOD
Original post by kimmey
come on guys lets not get off track talking about other subjects, keep this strictly chemistry haha

okay... what methods are there of making sure you only get one optical isomer ?

give me the equation for how D2O removes the OH group in ethanol during H NMR


Making sure you get 1 optical isomer:

Use bacteria or enzymes, as these are both stereoselective
Use chiral pool synthesis
Use a chiral catalyst (transition metal complex)
Start off with a natural chiral compound, such as amino acids
Original post by kimmey
yep you're on the right track your first point is right, not too sure about your second, i would say use bacteria or enzymes, and chiral pool synthesis.

for the second one you have CH3CH2OH + D2O ---> CH3CH2OD + HOD


THANKS!! :biggrin: btw where is that equation in the book? but thanks for letting me know :smile:
Reply 92
Avatar for kimmey
kimmey
7
Original post by Fatima0065
THANKS!! :biggrin: btw where is that equation in the book? but thanks for letting me know :smile:


i think so, i have seen it somewhere, try the beginning of the H NMR section
When an amino acid recats with an acid it forms a salt right?
and when it reacts with a alkali it forms, for example, if it reacts with NaOH...then the cooh = COO-Na+...but what happens to side chains of COOH...do they react in alkaline conditions to form coo- or if naoh is present coo-na+ aswell? can someon please explain this to me thanks :smile:
ANYONE KNOW WHAT TO DRAW WHEN AN IMPURITY IS FORMED???? (is there someething specific) :smile:
For question 2c(i);

http://www.a-levelchemistry.co.uk/OCR%20Chemistry%20A/Unit%204/Past%20Papers/Unit%204%20June%202010.pdf

Why, as a result of alkaline hydrolysis, does the OH not also form O-Na+ like the carboxylic acid group....in the mark scheme, a mark is deducted for writing O-Na+ for the OH group.....but for other questions I've done, it was correct to form a sodium salt from the alcohol group (in the absence of the COOH group though)
Original post by splendidsun
For question 2c(i);

http://www.a-levelchemistry.co.uk/OCR%20Chemistry%20A/Unit%204/Past%20Papers/Unit%204%20June%202010.pdf

Why, as a result of alkaline hydrolysis, does the OH not also form O-Na+ like the carboxylic acid group....in the mark scheme, a mark is deducted for writing O-Na+ for the OH group.....but for other questions I've done, it was correct to form a sodium salt from the alcohol group (in the absence of the COOH group though)


The OH does not form an O-Na+.

The OH group of a carboxylic acid or phenol are the only groups that will react with NaOH to produce O-Na+, not just an OH on a normal alcohol. The alcohol OH group will only ever react with sodium metal to produce O-Na+.

Maybe on past mark schemes you mixed this up with OH on a phenol. OH on a phenol and OH on a normal alcohol act as two different functional groups.
(edited 11 years ago)
Original post by Fatima0065
When an amino acid recats with an acid it forms a salt right?
and when it reacts with a alkali it forms, for example, if it reacts with NaOH...then the cooh = COO-Na+...but what happens to side chains of COOH...do they react in alkaline conditions to form coo- or if naoh is present coo-na+ aswell? can someon please explain this to me thanks :smile:


Are you talking about Zwitterions and isoelectric points etc.?

In acid conditions, the NH2 group on an amino acid protonates and becomes NH3+. The COOH stays as COOH. Any side chains with NH2 in will also become NH3+

In alkali conditions, the NH2 doesn't change and the COOH becomes COO-, if the alkali is NaOH then this will become COO-Na+. The side chains of COOH in alkali conditions will also become COO-Na+
Original post by racheatworld
Are you talking about Zwitterions and isoelectric points etc.?

In acid conditions, the NH2 group on an amino acid protonates and becomes NH3+. The COOH stays as COOH. Any side chains with NH2 in will also become NH3+

In alkali conditions, the NH2 doesn't change and the COOH becomes COO-, if the alkali is NaOH then this will become COO-Na+. The side chains of COOH in alkali conditions will also become COO-Na+


ooooh i get it...thankyou! :biggrin:
Original post by racheatworld
The OH does not form an O-Na+.

The OH group of a carboxylic acid or phenol are the only groups that will react with NaOH to produce O-Na+, not just an OH on a normal alcohol. The alcohol OH group will only ever react with sodium metal to produce O-Na+.

Maybe on past mark schemes you mixed this up with OH on a phenol. OH on a phenol and OH on a normal alcohol act as two different functional groups.


ah makes sense!!

thankssss! :biggrin:

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