Unit 3 Questions MEGATHREAD :)

[Asx4Life]

1a)For CH3CH2CH2CH2CH3 how many H environments are there?
b)For each environment, how many splits will they produce?

2a)For CH3CH2CH2CH3 how many H environments are there?
b)For each environment, how many splits will they produce?

3)What is the ratio of areas under peaks for propane? I thought it was 3:2:3. But answer says 3:1
For 2chloropropane, I thought it was 3:1:3, but answer says 6:1 do we need to add the Hydrogens that are in equivalent environments?

4)Take propanol as an example. What is the group of atoms that produces triplet?

5)What does peak height and peak area represent in HPLC/GC. Is is the same?

Just need some help on NMR where I'm weak at. Thanks VN!! =)

1. a) 3 different H environments (note the symmetry)
   b) 3 peak sets: triplet, 'pentet', 'hexet' (you know what I mean )

2. a) 2 different H environments (note the symmetry)
    b) 2 peak sets: triplet, 'hexet'

Note: I'm not taking into account multiplicity, and hence, could be wrong here

3. a) Propane has only two different H environments. 6 H : 2 H = 3:1
    b) 2-chloropropane has 2 different H environments. 6 H : 1 H  = 6:1. Yep, you need to add.

4. Assuming primary alkanol (ie propan-1-ol). The reading will be from either the CH3- at the end or the bolded hydrogen in -CH2-(OH). This is because the adjacent carbon to each group had 2 H (in -CH2-), hence a split of 3 peaks (just take it as the 'n+1 rule', but there is a more complicated reason based on nucleus spins and those combinations)

5. Not sure on peak height, but I don't think it means anything except that if there is a peak, there is a Rt for a specific component. The area gives the relative amount.

For question 2, I originally thought the same thing as you, but the answer is actually 2 singlets, because the molecule is symmetrical on both sides. Can anyone confirm this?

Thanks for the clarity on question 3.

Question 4 is the problem, the splitting of the environment CH3 causes a triplet. But the group of atoms that actually causes a triplet is the neighbouring carbon atom of CH2. Can anyone clarify this?

I thought area means concentration and height means amount?

Moderator action: removed real name, sorry for the inconvenience

[Greatness]

Mm i think if a molecule is symmetrical it only has singlet..

[Greatness]

Thank you. And also engage said that the bonding between deoxyribose and phosphate is hydrogen bonding. Is that correct? Or is it covalent?

Yeah it's covalent, more specifically phsphodiester.

[nacho]

do we need to know PCR?
I just saw it come up in an exam, and it wasnt in nelson textbook..
also, do we know how a 'DNA profile can be obtained from a sample of blood taken from a crime scene?'

[Greatness]

do we need to know PCR?
I just saw it come up in an exam, and it wasnt in nelson textbook..
also, do we know how a 'DNA profile can be obtained from a sample of blood taken from a crime scene?'

Yes we have to know that. I dont think we need to know the specifics but all you have to know is that you chuck some DNA samples (or amino acids) into the negative side of the machine, bigger molecules i.e. the ones with higher molar masses move less, smaller molecules move further, negative molecules move further as they are attracted to the positive side of the gel/machine thing and positive ones move less.
Dna profile is pretty much what the samples look like after they have been run in the machine. So you will get different bands at different places of the gel. From here you can match the bands with someone elses and determine who the criminal is etc.

[vea]

In Q2 of Asx4Life's Qs, there are two peaks, a triplet and a 12 multiplet (if there is multiplicity... VCAA shouldn't ask this though). I've no idea where the singlets come from.

[scocliffe09]

do we need to know PCR?
I just saw it come up in an exam, and it wasnt in nelson textbook..
also, do we know how a 'DNA profile can be obtained from a sample of blood taken from a crime scene?'

Yes we have to know that. I dont think we need to know the specifics but all you have to know is that you chuck some DNA samples (or amino acids) into the negative side of the machine, bigger molecules i.e. the ones with higher molar masses move less, smaller molecules move further, negative molecules move further as they are attracted to the positive side of the gel/machine thing and positive ones move less.
Dna profile is pretty much what the samples look like after they have been run in the machine. So you will get different bands at different places of the gel. From here you can match the bands with someone elses and determine who the criminal is etc.

That's not actually PCR - you described gel electrophoresis. And I think an awareness of both techniques is useful.
PCR - DNA replication in a machine.
Electrophoresis - run chopped up fragments of DNA through a porous gel. Be able to label terminals, and remember shorter fragments move further.

[nacho]

this is my PCR revision lol
http://www.youtube.com/watch?v=x5yPkxCLads
damn im so unsure about the exam..hopefully it is a neap style exam

[Greatness]

do we need to know PCR?
I just saw it come up in an exam, and it wasnt in nelson textbook..
also, do we know how a 'DNA profile can be obtained from a sample of blood taken from a crime scene?'

Yes we have to know that. I dont think we need to know the specifics but all you have to know is that you chuck some DNA samples (or amino acids) into the negative side of the machine, bigger molecules i.e. the ones with higher molar masses move less, smaller molecules move further, negative molecules move further as they are attracted to the positive side of the gel/machine thing and positive ones move less.
Dna profile is pretty much what the samples look like after they have been run in the machine. So you will get different bands at different places of the gel. From here you can match the bands with someone elses and determine who the criminal is etc.

That's not actually PCR - you described gel electrophoresis. And I think an awareness of both techniques is useful.
PCR - DNA replication in a machine.
Electrophoresis - run chopped up fragments of DNA through a porous gel. Be able to label terminals, and remember shorter fragments move further.

Hahahah yeah i did too.... whoops this is what kills me in the exams :/
Have VCAA tested this much in the past few years? Because from a fwe of the exams ive done they usually incorporate all of PCR, gel electrophoresis, sometimes restriction enzymes into one big SA question.

[scocliffe09]

Hahahah yeah i did too.... whoops this is what kills me in the exams :/
Have VCAA tested this much in the past few years? Because from a fwe of the exams ive done they usually incorporate all of PCR, gel electrophoresis, sometimes restriction enzymes into one big SA question.

Yes - you're exactly right about the SAQ - they're more interested in you understanding that we exploit some of DNA's properties to analyse it (universality, redundancy, negative charge, fragmentation following cleavage by restriction enzymes).

[mickeymouse]

with the vcaa 2010 qns 1b they accepted an answer with 4 sig figs but than the other parts were in 3 sig figs?

[pi]

Could someone give me hand with these ones please?

1. Am I right in saying that when a phosphate isn't bonded to a nucleotide and sugar, it has 3 OH groups? Does that mean that the phosphate at the end of the DNA chain will still have an -OH group attached to the phosphate?

2. (attached) The answer is A btw Solved now, thanks tony3272! 


Thanks a lot guys 

[tony3272]

Could someone give me hand with these ones please?

1. Am I right in saying that when a phosphate isn't bonded to a nucleotide and sugar, it has 3 OH groups? Does that mean that the phosphate at the end of the DNA chain will still have an -OH group attached to the phosphate?

2. (attached) The answer is A btw


Thanks a lot guys 

just for Q2.
Glycine has 1 nitrogen, whereas urea has 2. Therefore the ratio of glycine : urea is 2 : 1
If you work out the mol of glycine you get 1/75mol, which you then half and multiply by 60 to get the mass of urea.

Moderator action: removed real name, sorry for the inconvenience

[pi]

just for Q2.
Glycine has 1 nitrogen, whereas urea has 2. Therefore the ratio of glycine : urea is 2 : 1
If you work out the mol of glycine you get 1/75mol, which you then half and multiply by 60 to get the mass of urea.

Cheers Makes sense now!

[scocliffe09]

Could someone give me hand with these ones please?

1. Am I right in saying that when a phosphate isn't bonded to a nucleotide and sugar, it has 3 OH groups? Does that mean that the phosphate at the end of the DNA chain will still have an -OH group attached to the phosphate?

2. (attached) The answer is A btw Solved now, thanks tony3272! 


Thanks a lot guys 

phosphate is a derivative of phosphoric acid - so it depends entirely on the environment as to whether you have H3PO4, PO4 3- or anything in between. It is probably possible, if it were an acidic environment, to protonate the phosphate group but I don't think you need to know details.

Moderator action: removed real name, sorry for the inconvenience