Horza2002

The acidity of a given proton is dependant on how stable the resulting anion is. For example, carboxylic acids are fairly acidic because the resulting anion is delocalised onto two oxygen atoms (see the attached file above). So essentially, each oxygen atom can be though of has have 1/2 a negative charge. In the case of the green polyene in the file, the deolcalised anion is spread onto six carbons atoms so essentially each as 1/6 a ngetive charge.

Another way to look at the bond strenth/length is that as you increase the bond order (single to double to triple....etc) then you are putting more negative charge between the two positive nuclie of the bonds and so they attract each other more and is therefore stronger...you could also say they are stronger because, to break the molecule apart, you have now got two bonds to break. Certianly in organic chemistry, the vast majority or bonds are roughly the same length (there are a few exceptions), so on the whole, one molecules "density" is about equal to that of another...although in chemistry, the electron denisty of a molcules is far more important than where the nuclie are.

The bond strength does very much depend on the reactivity of compounds. That is why peroxides are explosive, the oxygen-oxygen single bond is pretty weak so if you heat it up too much, it breaks. Silicon-fluorine bonds (the strongest single bonds there is) are very stable and are basically unreactive. This also translates to higher bond orders as well....nitrogen gas has a triple bond between each of the atoms and is therefore not very reactive to other species (thats not to say it is completely resistant)

http://www.bupa.co.uk/health-information/directory/v/anaemia-b12

This does say that Vitamin B deficiency can adversally affect your nevers...so it is possible that could explain some of the symptoms your patient is suffering from.

Piridoxin is more commonly known as Vitamin B6. I know that Vitamin B6 is important in the biosynthesis of serotonin, epinephrine and dopamine hormones.

Missiippichem has given you the physical chemists views on delocailsation...so I thought I'd give you the organic chemists version. Just remember that they are exactly the same, just explained in a slightly different way.

In terms of conjugated systems, delooclisation implies that the electrons can be spread out of several different atoms throught the bonds that connected with. If you like, in a single bond and unconjugated double bond, the electrons stay between the two atoms that are making the bond (ignoring the small contribution from the Hiensburg uncertainity principle). However, when you make conjugated double bonds (double bonds seperated by a single bond), then the pi-orbitlas are able to overlap and so the electrons can now be "spread" out over several bonds. In fact, conjgation is a major tributing factor to acidity of hydrogens in molecules. If the resulting anion is stabilised by delocalisation, the hydrogen is more acidicThe majority of the mass in a molecule comes from the atoms it is made of since electrons mass is soooo much smaller than that of the nuclei.

In the case of benzene, once the orginal molecular formula was determined, they said it was a 6-membered ring with alternating single/double bonds. Since double bonds are shorter than single bonds, Kekule structure, this would lead to an odd shaped ring (see file attatched). But as Missiippichem has already said, the bonds are actually halfway between being a single/double bond. The C-C bonds in benzene are 140pm; a normal C-C single bond is 147pm and a double bond is 135pm.

Well, a single bond referes to a pair of electrons where the bonding orbtial is between the two atoms....a double bond has two pair of electrons.....and triple bond has six pairs....but once you add in conjugation, then it all starts getting a bit muddy.

P.S. Please ignore the awful spelling....I have only just woken up!

delocalisation.pdf

First of, I would determine the empircal forumal from the elemental analysis you have been given.

O, and I think your missing something important about regarding the melting point bit

I've just watched that viedo...and what they talk about is, I would say rather speculative. There is no evidence that it would work for humans...mammals are a much more complicated organisms than the worms they had got it to work with so far. Even if it is possible for humans, it is still decades away.

Genetic engineering will not allow us to live for ever. At the best, it will allow us to live for a long time...but you are still forgetting accidents....people will still die froma accidents (whether it being human error or technological faliure).

What scientists say we'll be alive in 3000? Can you send the links please, I'd be very interested in reading that please.

No death??........are you serious? People will still get old, ill, accidents and murder...people will still die. There is nothing you can do to prevent death from occuring. And pain and suffering are a natural part of life...to quote a line from Suviver, Rise Against:

"Life for you been less than kind

So take a number stand in line

We've all been sorry, we've all been hurt

But how we survive

It's what makes us who we are"

I agree with you, life without pain and suffering would be wonderful....its just not practically possible

How does becoming a civilisation mean our diaterary requirements change? We are still animals at the end of it all

I love animals as well...but you are forgetting that we are animals as well. We need to eat and meat has been a part of the human diet for a VERY long time. If we werent supposed to eat meat, we wouldn't have the enzymes required to digest meat or the teeth nessary to chew it properly. It is part of nature, everything that live needs to eat...we are no different to a lion in that we eat meat. If anythign we are kinder to the animals than a lion is...a lion will chase/stalk its prey until it exhausted (all the time the prey knowing what is going on) before it moves in for the kill...and its rarely a quick death..more a lingering death. Animals that are slaughtered for human consumption are often done in the most humane ways possible resulting in a quick death. And during thyre lives, they have all their needs cared for...they have no need to worry about predators, food, water, shelter, mates, etc.

While I don't hunt myself, I have no problem people hunting and killing animals PROVIDED they are going to eat them. I don't agree with people going out and killing animals for the fun of it.

As Mississippichem as said, conventional halogenation reactions don't work for flourine...you typically have to use special flourinating agents.

I have some experience with diethylaminosulphur triflouride (DAST). If you react DAST with an alcohol, you get the corrosponding alkyl flouride while reacting it with aldehydes or sterically unhindered ketones gives a geminal difluoride (two fluorines bound to the same carbon). There are also a wide range flourinating reagents...this link summarises the most common.

http://www.scripps.edu/chem/baran/images/grpmtgpdf/Su_May_08.pdf

http://www.alfa.com/en/docs/FluorinatingAgents.pdf

One if find really interesting is using xenon difloruide (XeF₂)...it converts a carboxylic acid into a alkly flouride with a carbon less (carbon dioxide is release). It reacts via a xenonalte ester and release flouride ions. I've done this reaction and it actually works rather good...xeon diflouride is also a nice white solid.

Anyone else think watching Nick Clegg or David Cameron doing the time warp would be one of the most distrubing sites imaginable...

http://www.gizmag.com/new-material-steel-plastic/18013/

Apparently, it is now possible to combine the strength of metals with the flexibility of plastics. However, these new materials still require large amounts of expensives metals for synthesis...even so, might be a useful intermediate along the way to developing organic polymers with the same strength properties.

I'm pretty confident in saying that anything that appears to be magic now, will be fully explained in the future. You just need to look to history...lots of things people attributed to magic/divine intervention have been explained in natural terms

Yer those pretreated plates are not really that great. We have them and you can hardly ever see it. Its far far far FAR better to use a TLC stain; have a look at one of my posts in organic chemistry for a list of stains and what they do.

Well Mohr's salt is actually ammonium iron(II) sulphate (NH₄)₂Fe(SO₄)₂. As a guess then, it might be taken as an iron suppliment for people suffering from iron defficiency. Iron is extremely important in biology so iron deficiency is a major problem.

What did you do to the plate before you placed it under the UV light? As I said though, a permanganate or vaniliin stain would have been much muhc better tand showing surcrose

...I have never heard of that visulisation technique before...how did you do it? Or was it you just help the plate under a UV light? If thats the case, then the compound needs to have some functional groups active to UV light (e.g. aromatic rings and double bonds). In the case of sucrose, I would be very very suprised if was visible with UV light...you should have used permanganate or vanillin as the stain...sucrose would show up VERY brightly using those stains.

You shouldn't use water as a cosolvent no...the water will be able to pick up protons from the silica gel and so you will have localised differences in the pH which will therefore alter your retention time. Some solvent systems naturally just run slower than others...

While yes, you can use the same solvent for the mobile phase that you used to dissolve the sample in; however I wouldn't recommend it. Typically you should use a solvent that dissolve your sample extremely well and so if you use it as your mobile phase, it will move very fast as far up the plate. So it yes indeed possible, but not advisable.

What where you using to visulise the spots? Im guessing that you used permanganate solution...

It could be that you didn;t put enough sample onto the TLC for you to be able to see any spots forming...it also be that the solvent systems were too polar and you compound just raced off the top of the plate. However, if you didn't see any spots at all anywhere in the plate, I would say that you either didn't put enough sample on or you used the wrong visulising method to detect them.

If you used straight ethanol on the second one, then you would have serious problems of the silica dissolving and therefore giving you heterogenious stationary phase to flow through.

What makes you think that, just because for us to perseve the world via electrical signals, that means the world doesnt exist? And how then do you explain that everyones perception of the physical world is exactly the same (ignoring the normal changes resulting from relativity). If I drop an apple it will accelerate towards the Earth at 9.8ms^-2. If you drop an apple, it will also accelerate at 9.8ms^-2. If lemur drops and apple, it will accerlate at 9.8ms^-2...how do you explain that we all observe the same properties if nothing exists?

That all depends on what you are TLCing. If you have a very non-polar molecule (basically only containing carbon, hydrogen and halogens), then a non-polar solvent system will be needed (e.g. hexane, hexane/diethyl ether, petroleum ether). If you have a slightly more polar molecule (containing protected nitrogens, oxygens, sulphurs or lots of them) then you'll need something more polar (hexane/ethyl acetate, ethyl acetate, dichloromethane, acetone). If you have an even more polar specicies (carboxylic acids, unprotected nitrogens, phosphonium salts) then you'll need something very polar (DCM/methanol). You can't really go above 10% Methanol though as you start to affect the homogenousity of the silica gel.

Those are the basic rules, but normally you have to play around with varying system until you find one that works. I normally start at 50% ethyl acetate in hexane as a baseline and then change in from there. It does massively depend on the compound that you are using though.

O, and the stationary phase is also important. Normally, silica gel is acid, and so amines do not move as they get protonated. There are several ways around this problem; either add a second base (normally triethyl amine) that neutralises the acid silica so your amine doesnt stick. Alternatively you could use alumina (aluminium oxide) as the stationary phase, which is basic in nature.

Ok according to Web ok Knowledge (WOK), the top 10 subject areas in 2010 are shown below with the number of papers/articles published:

1. Biochemistry and molecular biology = 54,558
   
2. Pharmacology and pharmacy = 37,634
   
3. Neuroscience and neurology = 36,689
   
4. Chemistry = 33,166
   
5. Genetics = 31,355
   
6. Physics = 32,136
   
7. Oncology = 29,118
   
8. Cardiology = 27,894
   
9. Engineering = 28,579
   
10. Material science = 23,755
    

In total, there were 445,806 papers published in 2010 according to WOK. As CharonY has said though, what are you classing as a subject area. But remember, this is just a list of paper published in each subject, not nessarily them claiming a new discovery.

That would make sence yes. Typically carbons up that end spectra are normally carbonyls so an imine would be there as well. Aldehyde protons are typically around 9ppm so an imine one would be a little lower but also higher than expected. That is the product I came to aswell

I didn't give the methodology since I have always been told what the various percentages translate to for concentration...just assumed that was the same everywhere.

The density you have given is wrong; 98% sulphuric acid is 1.83g/ml. Ok so heres the method you need to use in the attached file.

Once you have the concentration of the stock solution, you should easily be able to calculate what you need.

Volume.pdf

It is not the food intself that makes you ill, its is whatever has contaminated the food is what causes you to be ill. In most cases, you get food posioning if food is contaminated by bacteria that were not killed by the cooking process. Fungi and viruses can also contaminate your food as well.

Typically, the most common food posioning results from bacterial contamination (E.coli, Salmonella, etc) that then bread in your gut (again provided they survive passing through the stomach). As they grow, they often release toxins into your gut which is what actually makes you ill.

So any food that is capable of sustaining bacterial growth...and again, the different pathogens grow in different foods. Salmonella is normally caught by eating infected poultry, including eggs, whereas Bacillius cereus is often caught from undercooked/reheated rice. It all depends on what your eating.

The best way to avoid food posioning is proper food hygine and cooking food properly.

Removed so as not to just give the anwser without showing you the method; see next post.