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    Everyone ready?
    What are people dreading? :eek:
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    Probably Biochemistry cos I haven't got round to revising it!
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    Me neither
    Hopefully we wont get a horrible set of questions on the unifying concepts paper
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    Me neither
    Hopefully we wont get a horrible set of questions on the unifying concepts paper
    Its a cet we will..they have been in every pass paper unfortunately.

    Im dreading Biochemisty as well - given i havent revisied it yet!!
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    How about chains, rings and spectroscopy?
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    unifying concepts!!!
    2many different types of calculation
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    I'm sacred of all of it!!! I'm retaking chains, rings and spectroscopy from January and I've forgotten all of it! Unifying concepts and me don't get on... I only do well if i can learn stuff off by heart but anything could come up in this paper!
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    unifying concepts is ok, but all the rest suck! i do biochemistry and havent even started revisisng. Chains and rings is ok, but i lose marks for forgetting basic reaganst and stuff. got biology to do before that. wednesday and this weekend will be chemistry time!ooh..fun
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    I will be straight, will se up a thread for any good person on spectroscopy, to please xplain. or if anyone could do that in this thread, Basically, does any one have a grip on spectroscopy?
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    (Original post by mikeA1)
    I will be straight, will se up a thread for any good person on spectroscopy, to please xplain. or if anyone could do that in this thread, Basically, does any one have a grip on spectroscopy?
    Right I've dug this out of the back catalogue of my "helpful" contributions...enjoy it

    -------------------------

    Rule one: read the question which may give hints as the nature of any definitvie groups, like carboxylic acid, phenol, aryl.... then if you have the empirical formula try and work out what it looks like then build your answer around 3 or 4 possible models (if you feel comfortable doing this and have time)


    Mass Spec:
    look for the tallest peaks. find the largest one first (as in greatest mass) as this is the molecular ion peak. then look for peaks which could be obvious structural groups - carboxylic acid groups, methyl groups, benzenes always a good one. the thing to remember is the tiny peaks either side of the large ones are just atomic isotopes due to C13 and occasionally deuterium. there may be a small "TMS" (tetra methyl salicate) peak but this is usually labelled and doesnt present too much of a problem. in an A Level paper they're unlikely to confuse you with all the other stuff that appears though its usually quite obvious.

    IR:
    My personal favourite (if I had to choose). ones to look out for are the -OH groups which are around the 3000 mark. in alcohols this is a larger dip further to the left. in carboxylic acids its a shorter dip on the right of the 3000 mark, quite broad. the other one to look out for is the sharp peak at about 1700 - this is C=O. if you have this and an -OH peak just below 3000 its almost certainly a carboxylic acid, but check just in case.

    NMR:
    Absolutely, (well on ocr salters anyway - which is what i do). They give you the reference sheets anyway. When it has a range of possible values this is down to interference from adjacent protons (hydrogens). Draw out each component as you identify it. Then go for the "splitting technique".... if you check out the peaks for each chemical shift you see they're split. Count the number of "subpeaks" and subtract one. this is the number of hydrogens on the adjacent carbon atom. so if you have a peak at the chemical shift for R-CH2-R and it has 4 sub peaks, there are 3 carbons on on of the R groups. Then look for a chemical shift suggesting R-CH3. If this had 3 subpeaks then you've found yourself a CH3 group bonded to a CH2 group....making a H3C-CH2-R component.

    Don't worry too much about this type of question. Analytical chemistry is weird because, as in IR spec, you get not only the stuff which tells you what groups are around, but all the other "crap" from interference. This is usually eliminated anyway in an A Levelpaper, but some is still left in in an attempt to throw you off the scent.
 
 
 
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