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Everything posted by Horza2002

  1. As Cap'n Refsmmat has said, the issue would be how do you prevent the radioactive material scattering over a very large area of the planet if anything went wrong.
  2. To be honest, if I was in a car and a tsunami was heading towards me, I would be FAR mroe worried about being sweep away and crushed against something then drowning! Look at the photos from Japan, cars are just swept away....being crushed os far more dangerous than drowning! To be honest, if I was in a car and a tsunami was heading towards me, I would be FAR mroe worried about being sweep away and crushed against something then drowning! Look at the photos from Japan, cars are just swept away....being crushed os far more dangerous than drowning!
  3. It seem's odd then, that noone, including me, in our lab drink tea or coffee.....I tend to find drinking water is far more refreshing than coffee.
  4. Nuclear physics.....clues in the title..
  5. If you started with the peroxide dianion, then you would get hydrogen peroxide in water; it would deprotontate the water in the same way as the oxide anion would. But seeing the guy seems to be asking about forming O-O bonds, then its not useful.
  6. The sodium will be coordinated more than the potassium and the lithium will be even more aswell. However, I seriously doubt any of them will dissolve in toluene as they are all ionic. Enolate salts are sparingly soluble in THF but is soluble in DMF. Another version you could try is to use a strong base (e.g. LDA or NaHMDS) to completey deprotonate the enolate; this would mean that the rate of reaction will be dependant on the rate of palladium insertion into the C-Br bond (which is very fast). You would need to use a very bulky base, both the ones I suggested should be good, to reduce the amount of addition to the nitrile. I know they said in the paper that strongbases didn't work, but they point out that eeach reaction is different.
  7. Reacting the oxygen dianionn O2-, with water will give you two moles of hydroxide. The oxygen dianion is the conjugate base of hydroixde (i.e. what you get if you were to deprotonate hydroxide). Obviously, this is very hard to do and so the oxygen dianion simply deprotonates water so fast it doesn't have chance to do anything else: O2- + H2O ==> 2 HO- So, no, it won't give you hydrogen peroxide
  8. As this sounds like homework, post what you think the mechanism is and I'll then give you some advice. The sodium borohydride mechansim is very similar to that of lithium aluminium hydride with the major exception that the sodium does not coordinate to the carbonyl. See if you can work it out....I'll be happy to check any ideas you have
  9. While I am not sure, I cant think if several potential issues with a reaction like this. The first one will be the length of the linking carbon chain...if it is too short, then the reaction will be very slow because the resulting ring will be very strained. From reading the paper, they observer that the different reactions need different bases. One potential reason is the solubility of the resulting anion. I know that various sodium salts are pretty insoluble in THF as a solvent...and I would imagine they will be even more insoluble in toluene. I don't have much experience with potassium salts but I would expect that they are similar. Additionally, I would guess that there is a difference between the sodium and potassium enolate reaction rate with the palladium complex. In the case of the potassium case, the rate of palladium insertion is much faster than the rate of deprotonation. As a result, there is not enough enolate anion present to react and so the palladium complex is reduced to give the reduced product. In thase case of the sodium, the rate of deprotonation is faster and so there is enough of the enolate anion to react with the palladium complex.
  10. It has been characterised and was used in one of lectures; it is biosynthesised by a [2+4] cycloaddition. Now if I could only find my notes, I could tell you what it is....
  11. I don't personally know that book...however I would recommend: Biochemistry - Lubert Stryer, Jeremy Berg, John Tymoczko The Organic Chemistry of biological pathways - John McMurry, Tadhg, Begley These two are very good and are what I used for my degree; I also still use them now in my PhD.
  12. True, but HCl in your mouth is not exactly the nicest thing to do. And I'd like to point out that the equation you put up at the top is not complete. The complete one is: NaHCO3 + HCl ==> NaCl + CO2 + H2O It will probaby taste the same yes. Table salt itself is normally around 97% NaCl; the other 3% are made up of anticakign agents such as magnesium carboante or sodium silicoaluminate; it keeps the table salt free flowing. These additional compounds may contribute to the taste of table salt.
  13. This site allows you to get real-time updates on where Earthquakes occur and their magnitude. This is the last 7 days link: http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/quakes_big.php
  14. While yes, pyridinium chlorochromate is good at going to the alcohol....its is absolutely horrible to work with. For starters, is is highly toxic..very small amount can cause some very serious sideaffects. Additionally, the reaction can at time be so exothermic that you run the risk of the reaction catching fire (obviously dependning on what solvent it is). We did have an incident with that not so long ago. The byproduct of it is also absolutey horrible. It is a black tarry substance that doesn't dissolve very well in any solvent and also sticks very well to glassware. I have had the unfortunate experience of having to clean glass wear after a PDC reaction...that is the main reason I don't use it. TPAP (tetrapropylammonium perruthenate) is now my new favourite one. It is far more soluble than IBX and you only need a catalytic amount if you use a sarcafisal oxidant, typically NMO (N-methylmorpholine N-oxide). The side products can then very easilly be removed by passing through a plug of silica gel (no more than 2cm high is required). It has the other advantage that it is very cheap. As you only need a catalytic amount of TPAP, and NMO is dirt cheap, it works out as a much cheaper reagent to use than IBX. I've basically spent the week trying out the full range of alcohol-aldehyde oxidants...Overall, while IBX is useful, TPAP is the way forward for me I beleive.
  15. Hyper, maybe you should go away more often; we could get some good topics started Love you loads really!! As Hypervalent said, the best way to get the absolute stereochemistry is to get an X-Ray crystal structure so then you can actually see which centre you have. The problem is that not all compounds can be crystallised. The stuff I work on for example is not possible to get a crystal; that is why the stereochemistry was determined by comparing an authentic sample with two enantioselective synthetic analoguse using chiral HPLC.
  16. Calculate now many moles you need for 0.05M solution. Then work out how much of the concentrated acid you need. It will be good for you to do this yourself; I will be very happy to check them for you if you post them.
  17. Millilitres (ml) and centimeters cubed (cm3) are the same thing. It is just my persoanl prefernce to do my workings out in ml not cm3 .
  18. Yes, but it is extremely difficult to idenitfy one of those stereogenic centres. Especially when natural product are sooo complicted. The natural product that I am working on is relatively simple and only posses one stereogenic centre. It wasn't until the total synthesis of it was acheived did we know which entantiomer is actually was. What you say is totally correct...once you know one steregogenic centre, then you can assign the others. But remember the NOSEY will only help you if the stereogenic centres are close through space....if they are not, then you won't even be able to get the relative stereochemistry. Altering any of the stereocentres configuration won't help you because you still don't know what the absolute stereochemistry is. Chiral NMR solvents do exist yes. See the reference below: Application of chiral bidentate NMR solvents for assignment of the absolute configuration of alcohols: scope and limitations Yoshihisa Kobayashia, Nobuyuki Hayashia and Yoshito Kishi, Tetrahedron Letters, 44, 2003 However, the NMR spectra of a lot of natural product is just soooooo busy with signals, you siply can't see what is going on. I have never used chiral NMR solvents before mainly because they are far from foolproof and often the nessary interactions are to hard to see. To get the best results though, a high field spectrometer (600MHz or above) would be needed.
  19. Did I hear somebody call me? There are a range of reason as to why the racemate is synthesised first. In some cases, the absolute stereochemistry of the natural product is unknown so you don;t know which enatiomer you want. Another reason is ease and cost of the synthesis. Generally, it is far easier and cheaper to make a racemate than an enantioselective product; especially if you don't even know which enatiopmer you actually want! Nowadays, there are an awful lot of chiral catalysts that allow you to get high enationselectivity in reactions, but they are often pretty expensive. This is also a good way to devise an efficient synthetic route; especially as natural product synthetic routes tend to be very long. When a new natrual product is identified and its structure determined (using MS, MS-MS and NMR), the hardest job is assiging the absolute stereochemisrty of the chiral centres. Using NMR studies (typically NOSEY experiments), the relative stereochemistry between each of the stereocentres is normally the first step. Then to confirm the absolute stereochemistry, each enatiomer is synthesised enationselectivly and then compared to the orginal using chiral HPLC.
  20. Weel this structure is a corss between an acid anhydride and a carbonate and it attacking the carbonyl of the anhydride is consisten with my idea about the carboante being mroe stable. It is well known that the identity of the nucleophile has a pronounced impact on the regioselectivity of reactions. It might also be that Grignards and organolithium species are simply to reactive, even for these stabilised functional groups. It would appear that my initial guess of the additional lone pair is more important.
  21. No, its not shielding, but people had been using that terminology so far so I kept with it to prevent confusion. I havn't seen a reaction like this before...but I think that might due to non-specific reactions. If you look in the file I added previously, the inital product after the reaction is a diester. If I am right about the electrophilicity, then this will be more reactive than diethylcarbonate and so react again to give a mixture. In this case, the major product will be determined by which reaction is fastes; deprotonation of the dicarbonyl or attack of another enolate. I think I might have to have a look on SciFinder tomorrow when I get to the office to see if people have used this method before. I've just been having a look around actually, and I'm not so sure now. In protecting group chemisrty, carbamates (R-NH-C(O)-O-R) are more suseptiable to amides (R-NH-C(O)-R). Apparently Fmoc, Boc and Cbz (all carbamates) are more reactive to Grignards and organolithiums than an the corrosponding amides. I wonder if the additional lone pair of electrons actually destailises the structure more than the "shielding" of the carbon; we are adding another two electrons to the same pi-system. Im definately going to have to go do some research on this now...
  22. At the moment, I'm working my way through the Raymond E Feist Midkemia series. At the moment im on Wrath of a Mad God (number 20 of 24 released so far!)
  23. As I've said before on here, everything that lives must gets its nutrients from somwehre else....death is an intergral part of the natural cycle. It is impossible not to intervene with other animals lives...at the simplest level, we need the same land that they do...as well as food, water, habitate, etc.
  24. Essentially, a solute is soluble in a solvent if there is a net stabilisation (i.e. the solute-solvent interactions are more favourable than solvent-solvent interactions). In the case of NaCl dissolving in water, the interactions between the water molecules and the ions are more stable than those between water molecules. Yes, when a solute dissolves in a solvent, there is indeed energy released. Its is normally refered to as the "enthalpy of dissolution" and is often negative (i.e. favourable). A drop of dye in the bottom of a glass of water will slowly move upwards because of diffusion. Tbh, im not sure if gravity will have that much of an effect on chemical reactions....the mass of molecules is soooo tiny that gravitational effects are not used even when doing extremely sensitive calculations.
  25. Lol I would say that at the moment, there are several members who are really upto chemistry. If you have any questions, then post them on here...I enjoy the challenge!
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