Unit 3 Questions MEGATHREAD :)

[pi]

Disulfide Link/Bridge - Both ok?

Also, should we provide catalysts wherever possible in a reaction?

Both are fine, I usually go with disulfide link though

I try to, but if I forget, I just write 'catalyst'. Had a lecture (MHS + MacRob) with the chief examiner, and he doesn't expect knowledge of all catalysts (including ones like Ni, etc.). Main ones are H2SO4 and UV light from what I understood of him.

[eeps]

how many H environments in this molecule? CH3(CH2)3CH3

I thought there were 2 environments but the answer says 3?

I believe it's 3. The 2 CH3's at the ends makes one hydrogen environment. The 2 CH2's which are attached to the CH3's count as another hydrogen environment. The CH2 in the middle is another environment. In total, there is 3.

[mickeymouse]

thanks that makes sense

how do we attach scanned images? I have another question too long to explain...

[pi]

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[pi]

Phosphates in the data book, why do some exams say it contains OH while the data book shows O-?

I'd like to know this too! Not sure and different diagrams do different things. I THINK, that when it is in DNA, there is a O- (hence net negative charge of DNA molecule) and a =O coming from the P, with the other two Os being in phosphodiester bonds. Not 100% sure on this though.

EDIT: didn't see answer by homosapiens and mickeymouse, my bad

Is the order of polarity for organic molecules from least polar to most polar:
alkenes, alkanes, ether, ester, amine, carboxylic acids, alcohols, amide?
And if so, why are alkenes less polar than alkanes...

least polar -> most polar
alkenes, alkanes, amine, alkanol (note, O has a higher electronegativity than N), carboxylic acid. Not sure on 'ester, ether, halogen and amide', but they are between alkanes and amines, never seen those ones examined though.

Alkenes are as polar as alkanes, but have lower boiling points because there are less hydrogens, and hence, less net dispersion forces between alkene molecules.

 

[homosapiens]

Thanks pi for clearing that up!

Also about the phosphate group thing, I'm pretty sure the data book presents the phosphate group as if it's bonded to the deoxyribose sugar (ie it loses its hydrogens once it's bonded)

Moderator action: removed real name, sorry for the inconvenience

[pi]

Thanks pi for clearing that up!

Also about the phosphate group thing, I'm pretty sure the data book presents the phosphate group as if it's bonded to the deoxyribose sugar (ie it loses its hydrogens once it's bonded)

Yep, I think your right.

So, am I right in saying that when it 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?

Moderator action: removed real name, sorry for the inconvenience

[mickeymouse]

this is a solution to a question, pretty much an acid and base are titrated and 17.8mL of an unknown acid is used.
if it was a monoprotic acid wouldn't the mole of the acid be the same as that of the base?

btw thanks pi

Moderator action: removed real name, sorry for the inconvenience

[pi]

this is a solution to a question, pretty much an acid and base are titrated and 17.8mL of an unknown acid is used.
if it was a monoprotic acid wouldn't the mole of the acid be the same as that of the base?

btw thanks pi

If you write up an equation, lets see. eg. HCl
2HCl + Na2CO3 --> 2NaCl + H2O + CO2

There are 2 mol of monoprotic acid needed, as there are two mol of Na in the base. Hence, mol is double for the monoprotic. If we use H2SO4, we see that mole ratio is 1:1, etc for a triprotic acid (try phosphoric acid for example)

Moderator action: removed real name, sorry for the inconvenience

[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!! =)

[pi]

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.

[DavidSheena]

I guess this is a trivial question but If i get exactly the same answer as required and show different working do I still get awarded full marks?

And with sig figs: If there is a question with 4 parts and  the first part which is the explanation has two sig figs. And then the 4th part has 4 sig figs (granted  no calculations or values from the information provided in the explanation is used). Would two sig figs be sufficient or would it be four?

The answers said 4 I put 2 :S

[pi]

I guess this is a trivial question but If i get exactly the same answer as required and show different working do I still get awarded full marks?

As long as its fairly logical, it should be fine

[nacho]

god wow stav exams are hard..

[DavidSheena]

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