Chemistry 3/4 2013 Thread

[lzxnl]

Isotopes found can encompass all isotopes in existence...it's just that some are more common than others. That's why you rarely see carbon-13 for instance. However, as bromine 79 and bromine 81 are almost just as common, they will both contribute significantly to the mass spectrum.

The linkage holding the DNA backbone together is a covalent bond between a phosphate group and deoxyribose and looks like an ether linkage, although given the P=O bond, it's known as a phosphoester.

[thushan]

Isotopes found can encompass all isotopes in existence...it's just that some are more common than others. That's why you rarely see carbon-13 for instance. However, as bromine 79 and bromine 81 are almost just as common, they will both contribute significantly to the mass spectrum.

The linkage holding the DNA backbone together is a covalent bond between a phosphate group and deoxyribose and looks like an ether linkage, although given the P=O bond, it's known as a phosphoester.

Almost; some possible isotopes would not be found naturally as they would decay really quickly.

[aestheticatar]

Hey there,

How would I name the ester HCOOCH(CH3)2?
I saw it in a STAV exam and was just wondering.

Thanks again beautiful people.

[Sapphire]

Hey there,

How would I name the ester HCOOCH(CH3)2?
I saw it in a STAV exam and was just wondering.

Thanks again beautiful people.

that looks like 2-propyl methanoate, I could be wrong though

So, (I think) we're reacting 2-propanol and methanoic acid. When naming the ester, the alcohol part is 2-propanol - CH3CH(OH)CH3
and the acid part is methanoic acid- HCOOH, once they have reacted and a water molecule is lost, you are left with HCOOCH(CH3)2

Sorry for the poor explanation :/

[lzxnl]

Think methyl methanoate. On the methyl part of the ester, remove two hydrogens and replace them with methyl groups.
You'd actually have 1-methylethyl methanoate. The 1-methylethyl means the ethyl group has a methyl group on carbon 1.
It is also known as isopropyl methanoate.
Although the reactions are correct.

[Sapphire]

Think methyl methanoate. On the methyl part of the ester, remove two hydrogens and replace them with methyl groups.
You'd actually have 1-methylethyl methanoate. The 1-methylethyl means the ethyl group has a methyl group on carbon 1.
It is also known as isopropyl methanoate.
Although the reactions are correct.

ah, I stand corrected. Thank you
are you referring to the reaction between 2-propanol and methanoic acid? Is that one correct?

[lzxnl]

Yes, that reaction.

[drake]

It should be 2-propyl methanoate

[lzxnl]

http://en.wikipedia.org/wiki/Isopropyl_acetate
For the acetate/ethanoate, both names are fine apparently.

[Edward21]

Hey, I did a practice exam today, and one of the questions was what are 2 functional groups found in a lipid.
In my mind I envisioned a glycerol molecule bound to three fatty acid chains via an ester bond, and I was a bit stuck because I was like ok there's ester bond functional group, but where's another? So I settled for alkane and alkene functional groups (if unsaturated) but I'm not really sure. I totally understand IF it was glycerol you could say hydroxyl coz it's a tri-ol and for the fatty acid chain carboxyl, but in the case of a lipid, they've been merged so there's an ester bond haha, I was confused!

[thushan]

Hey, I did a practice exam today, and one of the questions was what are 2 functional groups found in a lipid.
In my mind I envisioned a glycerol molecule bound to three fatty acid chains via an ester bond, and I was a bit stuck because I was like ok there's ester bond functional group, but where's another? So I settled for alkane and alkene functional groups (if unsaturated) but I'm not really sure. I totally understand IF it was glycerol you could say hydroxyl coz it's a tri-ol and for the fatty acid chain carboxyl, but in the case of a lipid, they've been merged so there's an ester bond haha, I was confused!

Alkyl functional group...that's stretching it. Technically it is one...but I'm unsure as to whether they'd pay it.
Alkenyl functional group they should pay - it was paid on the VCAA exam once iirc.

Btw - there is an 'ester' functional group too.

[teletubbies_95]

Hii guyss!:)
I was just having trouble deciphering what the question(VCAA 2002)  was asking ? I dont understand VCAA's assessment report comment , "Solvent, Stanozolol" and how only "one peak " is formed.

A pure substance was suspected of being the high molecular weight anabolic steroid Stanozolol. A sample
of this substance was dissolved in a suitable pure solvent and injected into a gas chromatograph. How
many peaks would you expect to see in the resulting chromatogram? Justify your result.

Thanks so much !!

[brightsky]

Hii guyss!:)
I was just having trouble deciphering what the question(VCAA 2002)  was asking ? I dont understand VCAA's assessment report comment , "Solvent, Stanozolol" and how only "one peak " is formed.

A pure substance was suspected of being the high molecular weight anabolic steroid Stanozolol. A sample
of this substance was dissolved in a suitable pure solvent and injected into a gas chromatograph. How
many peaks would you expect to see in the resulting chromatogram? Justify your result.

Thanks so much !!

you might have misinterpreted the report. if the pure substance was dissolved in a suitable solvent before being injected into the gas chromatograph, two peaks would register, one due to the pure substance and one due to the solvent. (i think this is what 'solvent, stanozolol' is supposed to mean. perhaps 1 mark/2 marks was awarded to students who wrote that only one peak would be observed.

[Edward21]

What do you guys read from this? If there's a double-stranded section of DNA 100bp long, aka contains 200 nucleotides in total, you know 38% is G, therefore 38% is C, 12% T/A. One of the stranded contains 25 guanine bases, how many cytosine bases would be on the same strand? I got 51, tell me what you think it is, I basically said hmm, well 0.38*200 = 76 bases in total, yet on this strand there's only 25 thus 51 on the other strand, 51 on the other strand of G would mean 51 of C on the strand in question, yes? 

[thushan]

76 Gs in total - 25 on Strand 1, hence 51 on Strand 2; hence, 51 Cs on Strand 1.