Chemistry 3/4 2013 Thread

[thushan]

Make sure you know your individual reactions.

Then, working backwards is a good idea. Often, they will ask you to produce an ester from a set of organic compounds. A good way to think about it is - "what do I need to produce this ester? OK. Now, what do I need to produce these compounds? etc.etc."

[acciotardis]

Will we need to know how to calculate the absorbance values and be able to sketch an NMR spectra? If so, how?

Thanks

[jgoudie]

No sure what you mean by calculate absorbance values, but you should be able deduce the what NMR spectra of a given compound will look like.

Steps involved:
1) Chemical shift - What are the Hydrogens bonded to?  look at the data booklet
2) Relative Peak height - The number of hydrogens in the environment
3) Peak splitting - How many neighbouring hydrogens are there? (n+1)

Remember to add a little peak at 0ppm for the TMS standard.

Will we need to know how to calculate the absorbance values and be able to sketch an NMR spectra? If so, how?

Thanks

[teletubbies_95]

No . According to the study design , you don't need to know how to calculate absorbance values. There's some special formula for calculating absorbance( according to my teacher)
But what jgoudie mentioned is in the study design! so yeh!

[drake]

Hello, a few questions:

1. In an addition reaction with an alkene and water, what state is the catalyst H3PO4 in? Is it aqueous?

2. In organic reaction pathways, how does one determine the physical states of the reactants and products? E.g. I know in an esterification reaction, the products, reactants and catalyst are all in liquid form. But what about in the oxidation of alkanols as well as substitution and addition reactions, what are the physical states of the products and reactants there?

3. In chromatography, what is the difference between peak height and peak area? Why do we choose one in preference to another?

Thanks!

[Edward21]

Hello, a few questions:

1. In an addition reaction with an alkene and water, what state is the catalyst H3PO4 in? Is it aqueous?

2. In organic reaction pathways, how does one determine the physical states of the reactants and products? E.g. I know in an esterification reaction, the products, reactants and catalyst are all in liquid form. But what about in the oxidation of alkanols as well as substitution and addition reactions, what are the physical states of the products and reactants there?

3. In chromatography, what is the difference between peak height and peak area? Why do we choose one in preference to another?

Thanks!

For 1. I'm pretty sure (I have a really good memory) that the H3PO4 is a solid, whereby the alkene is passed over this solid catalyst at 300 degrees C with H20(g) to produce and alkanol

2. I wonder this too

3. Peak area is proportional to the amount of that substance, you draw up a calibration curve with the area under the peak vs known concentrations, to then use a peak area to work out the concentration/amount of the substance, if a peak is really high it means a LOT of that substance at a particular Rt is passing over the detector, but the peak area reveals a more accurate depiction, especially since not all of that particular sample may pass over the detector all at once and produce a tall thin peak, but rather a shorter wider peak! This is why area is more important than height of the chromatogram peak.  Check this out http://www.chemguide.co.uk/analysis/chromatography/gas.html

[memarani]

I need help with this question:

How many possible products are there when ethane reacts with bromine?
Draw the structures of the products of the substitution reaction.

The answer says there's nine possible products but i could only find six

Thanks in advance!

[lzxnl]

So...you can have products that have 1, 2, 3, 4, 5, 6 bromines. +6
As for the products with 2 bromines, they can be on the same or opposite carbons. +1
For the products with 3 bromines, you can either have two on the same carbon or three on the same carbon. +1
For the products with 4 bromines, you can have either three on the same carbon or two on the same carbon. +1.

I believe that's nine possibilities.

[memarani]

Another question, what is the difference between condensation, substitution and hydrogenation reactions concerning ethane?

Thanks again!

[Daenerys Targaryen]

Condensation: a reaction that results with water as a reactant and also polymerisation
Substitution: One atom is replaced by another e.g. a H on ethane is replaced by one Cl
Hydrogenation: Adding which replaces the Cl in chloroethanes

[lzxnl]

Condensation does not have to be polymerisation. Anything that forms water can be seen as condensation. If something has water as a reactant, it is either a hydrolysis or a hydration.
As for hydrogenation, I thought it referred to the addition of H2 over a double bond. I'm not entirely convinced that reacting chloroethane with hydrogen gas will produce a reaction unless you change the conditions significantly to reverse the chlorination reaction.

[jono88]

How would you name ch2(oh)ch2(oh)?

[brightsky]

ethane-1,2-diol

[jono88]

Doesn't it need to be in alphabetical order according to IUPAC?

[abcdqdxD]

Never question brightsky- he's a boss.