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

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Reply 980

pete clark

Original post by clad in armour

so why the hell in june 2011 6 a part ii, do they completely ignore it and dont count it
not having a go btw :tongue:

just very perplexed

http://pdf.ocr.org.uk/download/pp_11_jun/ocr_66605_pp_11_jun_gce_uf324.pdf?

because thats an ester and an Amide. :smile:

Reply 981

racheatworld

Original post by atman7

There won't be anything big just small markers I think the past papers are relatively good with the answers to majority of the questions about it. I'd say limitations is probably something that's not been up

This was posted from The Student Room's iPhone/iPad App

Thanks. There are quite a few definitions as well for chromatography (Rf values, retention time) but anyway...

Limitations of TLC:
- Rf values are similar for similarly structured compounds
- Unknown compounds have no reference values to compare to
- To compare unknown compounds the same conditions are needed, for example exact same solvent
- It is hard to find a good solvent for each sample. The components cannot dissolve too much in the solvent as they will not be separated, likewise they cannot adsorb too much on to the stationary phase as they will not be separated.

Limitations of GC:
- Retention times are similar for similarly structured compounds
- Unknown compounds have no reference retention times
- Compounds with similar retention times, can remain "hidden" behind other compounds in higher concentrations and therefore will not be detected.

(edited 11 years ago)

Reply 982

pete clark

Original post by Megan-89

Its because its next to a N so its a peptide... I think :smile:

You're clearly a Biologist :wink:

Reply 983

clad in armour

Original post by Magickal

Because the two C=O are part of the amide/peptide and ester groups :smile:

that would indeed make more sense, thanks very much :smile:

Reply 984

clad in armour

Original post by pete clark

because thats an ester and an Amide. :smile:

yep, makes sense thank you :smile:

questions

Can anyone explain question 4 a on jan 2011 for me? write the equation for the reaction between ClCH(CH3)COOH and excess ammonia

Reply 987

Magickal

Original post by Megan-89

Can anyone explain question 4 a on jan 2011 for me? write the equation for the reaction between ClCH(CH3)COOH and excess ammonia

It would turn to ClCH(CH3)COO-NH4+

Reply 988

Megan-89

Original post by pete clark

You're clearly a Biologist :wink:

Indeed I am :tongue:

Reply 989

pinkcherrytart

everything else im not even remotely worried about...its the NMR that i just can not get into my head..ive got 20 hours better get down to it

Reply 990

Magickal

For anybody struggling with NMR use this website, it is an absolute godsend
http://www.spcollege.edu/SPG/science/Musgrave/nmr.htm

Reply 991

pete clark

Original post by magickal

it would turn to clch(ch3)coo-nh4+

h2nch(ch3)coo-nh4+ ...

Reply 992

racheatworld

Original post by pete clark

h2nch(ch3)coo-nh4+ ...

That's what I thought. Excess ammonia will react with the COOH but also the halogen Cl on the other end :smile:

Reply 993

rasklatz

Can anyone confirm that on p89 the Heinemann textbook, worked example 2 is partially wrong since the molecular formula is C8H10 instead of C8H8?

Reply 994

pete clark

Original post by racheatworld

That's what I thought. Excess ammonia will react with the COOH but also the halogen Cl on the other end :smile:

correct.

Reply 995

darkxangel

low resolution NMR spectra:
-AREA under each peak is in direct proportion to the number of protons responsible for the absorption,
-it's useful for identifying:
-the number of types of protons from the number of peaks,
-the type of environment of each proton from the chemical shift,
-how many protons of each type from the integration trace,

-we can interpret the spin spin coupling pattern using the n+1 rule. For n-adjacent protons, the number of peaks is a multiplet = n+1,

high resolution NMR spectra:
-the chemical shift shows spin spin coupling pattern-it identifies the type of proton responsible for each peak,
-the n+1 rule can be used to identify the number of adjacent protons,

TMS:
-it's chemically inert and doesn't react with the sample,
-it's volatile and easy to remove afterwards,
-it absorbs at a higher frequency than other organic compounds, so that it doesn't overlap with the sample,
-all other peaks measured relative to TMS, it's chemical shift is set at zero,

D2O:
-The OH and the NH peaks have chemical shifts that are variable and sometimes outside the range,
-when alcohols, carboxylic acids or amines are dissolved in water, there is a rapid exchange between the protons in the functional groups-labile protons-and the protons in the water,
-if water is replaced with deuterated water (D2O), the peak at H disappears. The H proton is replaced by deuterium which doesn't absorb in this region of the spectrum,

-when samples are prepared for NMR it's often necessary to dissolve them in a suitable solvent,
-solvents containing hydrogen are clearly unsuitable as the hydrogen atoms in the solvent would also be detected and thus interfere with the spectrum. This is overcome by using deuterated solvents such as CDCl3,

Chirality:
-Can exist as plane-polarised light, optically active,
-extremely difficult to synthesise laboratory, it contains 50/50,
-only one of the isomer has the correct shape and is pharmaceutically active, vital that it's isolated,
-chiral chromatography is required,

(edited 11 years ago)

Reply 996

Magickal

I completely forgot about the NH3 reacting with Cl too >.<

Also guys if you missed it, this website is amazing for NMR:
http://www.spcollege.edu/SPG/science/Musgrave/nmr.htm

Reply 997

Megan-89

Original post by pete clark

h2nch(ch3)coo-nh4+ ...