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Everything posted by Horza2002

  1. Hypervalent iodine compounds are extremely useful...this was just a new reagent I hadn't come across before. In the end, I just washed with water lots of times and then evapourated the residual DMSO. Seemed to work fine...no columns or anything!
  2. I would have said that it was less reactive actually. Yes you do have two oxygen atoms pulling electron denisty away from the central carbonyl, but you also have an extra pair of electrons in conjugation with the system. An ester is less reactive than a ketone because the second oxygen's lone pair is in conjugation shielding the carbon. In carbonate, you have another pair of electrons shielding the carbon.
  3. Ok, within a water molecule, you have oxygen and hydrogen. Due to the relatively high effective nuclear charge of the oxygen nulcie, electrons around oxygen are more stable as they are closer to the nucleus. This means oxygen has a tendancy to pull electrons in a bond towards itself; its electronegative. Hydrogen, on the other hand, is not electronegative and so the electrons in the H-O bond are shifted towards the oxygen. This results in a partial positive charge on the hydrogens and a negative charge on the oxygen. When there are lots of water molecules around, this difference in charge results in the oxygen of one water molecule being attratced to the hydrogens on another water molecule. Since oxygen has two lone pairs, it can actually form a hydrogen bond with two other water molecules hydrogens. As a result, bulk water molecules (i.e. not on the surface) form tetrahedral structures with the hydrogen bonds holding everything in place. This is a very stable arrangement; the central molecule has four favourable interactions with four other water molecules and so is lower in energy than it would be on its own. Effectively, there is no net force on the molecules, they are being pulled by the same strength force from all directions. However, at the surface of the water, there are only water molecules on one side of the outer molecule. As a result, they are pulled towards to the bulk. Any water molecule on the surface will be less stable than being in the bulk because it can't have four hydrogen bonds around it. This molecule therefore higher in energy than those in the bulk. The system therefore attempts to reduce the overal energy of the system by making liquid have the lowest surface area.
  4. IBX does seem to have a large range of application and its a lot cheaper than the Dess-Martin periodate. DMSO is an ok solvent I have discovered...apart from trying to get rid of it at the ened of a reaction. So far, my only way to do it has been to swamp is with water to make my compound crash out as the DMSO goes into the water. Alterntively I have removed it by vacuum distillation a few times...anyone got ideas of how to get rid of it more easilly?
  5. Artificial meat would not solve the problem of excessively large populations of game animals. And while synthetic meat could indeed be possible, getting the flavour right would be extremely difficult...I'm not sure people would accept the change.
  6. Imatfaal, that is a very good idea. Something with alot preservatives would be very good to introoduce you to a wide range of compounds with several different functional groups. The chemical structure of all the E numbers are easily avaliable online...one pre-prepared meal will most certanily get 10 chemically interesting compounds of it.
  7. A lot of my synthetic routes at the moment require me to oxidise alcohols to aldehydes. Until recently, I have been using the Swern oxidation; while this has been working perfectly well, its just too fiddley keep everything at -78OC and anhydrous as well. I have since found the great hypervalent iodine oxidant 2-iodoxybenzoic acid (IBX); an older version the the Dess-Martin periodate. http://pubs.acs.org/doi/abs/10.1021/ol026427n This reagent is unfazed by air or moisture and is basically insoluble in almost all organic solvents. While this might sound pretty useless, as elevated temperatures, enough is soluble to make this reaction efficient. At the end of the reaction, simple filtration and removal of the solvent is required to give the desired aldehyde in close ot quantitive yields. Anyway, just thought I'd share this!
  8. The surface tension is a property of a liquid to minimise the total surface area. This arises because water molecules on the surface have the intermolecular on one side of them pulling them towards the bulk. The hydrogen bond pull the molecules on the sirface towards the bulk
  9. The surface tension is a property of a liquid to minimise the total surface area. This arises because water molecules on the surface have the intermolecular on one side of them pulling them towards the bulk. The hydrogen bond pull the molecules on the sirface towards the bulk
  10. The high boiling point of water is a direct result of hydrogen bonds between the water molecules; an intermolecular force. These are relatively strong so give water its high surface tension and high boiling point. If you look at the boiling points of the hydrogen chalcogen, water is indeed the odd one out because of the hydrogen bonds. The others in this group are not capable of forming hydrogen bonds and so boil at a much lower temperature. Hydrogen oxide H2O = +100oC Hydrogen sulphide H2S = -60oC Hydrogen selenide H2Se = -41oC Hydrogen telluride H2Te = -2oC Hydrogen polonide H2Po = Not stable Hydrogen ununhexiumide H2Uuh = Not been observed
  11. That is the molecular formula for sodium silicate yes. From what you have said, and if you your project is about the perodic table, then the teacher probably wants you to give the molcular formula for those 10 household items.
  12. http://en.wikipedia.org/wiki/Gene_therapy This gives agood general overview of the technique. http://www.macmillan.org.uk/Cancerinformation/Cancertreatment/Treatmenttypes/Biologicaltherapies/Genetherapy.aspx This gives some information regarding the cancer side of things. Doing so further reading, it seems the idea is to add genes to cancer cells that make them suseptiable to certain compounds. Alternatively, the damaged portion of the genes that actually cause the cancer could be replaced with the healthy version of it. So far, this is rather experimental for cancer and so while be a fair few years before this is widely used. Gene therapy is used in the treatment of cystic fibrosis where patients inhale a vector containg the healthy version of the gene which then replace the faulty ones of the patients airways.
  13. Wow, this is an extremely broad range of possibilities! I guess, the first step in identifying unknown compounds is get a high resolution mass spec. This will allow you go get a molecular formula for your unknown compound. This could then be linked further by MS-MS methods to montior the fragmentation of the parent ion...this would allow you to piece together the structure of molecule as they tend to fragment in very predictable ways. MS will also allow you to determine the overal charge of a molecule (specifically if it is a protein) and to a lesser extent, ionorganic complexes. Another useful method for metal containing compounds would be obtain a UV-Vis spectra. This would allow you to determine the enviroment and charge state of any metal ions contained within your compounds. This is essentially the modern version of the flame test; adding a small amount of the compound to a flame and seeing what colour it goes. Another useful step would also be a full NMR set of experiments; H-1, C-13, COSY, HMQC, HMBC, NOSEY, TOCSY, decoupling experiments all would be very useful. Then there are the old school "wet" tests...like adding silver nitrate to see if there is a hlaide present. A white precipitate forms for chloride (silver chloride), cram for bromide (silver bromide) and yellow your iodide (silver iodide). Or if adding barium chloride gives a precipitate, then you have a sulphate. There are loads of these sorts of tests.
  14. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0011250 This is one of the ones I've managed to refind. Im still looking for the others (my University has altered its Journal subscriptions which is not helping matters!)
  15. I'm not exactly sure what your asking here...it's not quiet making sense. A mixed Claisen condensation is a reaction between two different reagents (i.e. two different esters or an ester and another carbonyl compound). The example you have given above with diethylcarbonate and ethoxide can't undergo a Claisen condensation. As you have said, there is no alpha-proton and the two sets that are present in diethyl carbonate are not acidic enough to be deprotonated. The only thing that can happen here is the ethoxide anion attacking the carbonyl of the carbonate which will then eliminate an ethoxide to get you back to the start. However, if your were to do a mixed Claisen condensation using diethylcarbonate as your electrophile, then it would work (see attached file). This would be an efficient way to add an ester group in the beta position to your original carbonyl. claisen.pdf
  16. Acidity depends on how stable the resulting anion is (and other factors aswell). If the density of electrical charge (for lack of a better phrase) is low in the resulting anion, then the proton will be fairly acidic. The density of a substance does depend on the shape of the molecules to and extent; but it is not the only factor. If the compound is very branched, then it'l have a lower density because the molecules can't get that close together. Another contributing factor will be the strength of intermolecular bonds (Van der Waals, ionic interactions, hydrogen bonds). If these forces are strong, then the molecules will tend to get closer together...having said that, the lots of organic compounds have a fairly similar density. While I've been thinking about how to explain this, I have noticed that alot of the reasons are similar to those that affect boiling/melting point actually. Having weak bonds means that it takes very little to break them..and the bonds that are made are even more stable. So you can get essentially chain reactions...a weak bond breaks and releases alot of energy making the new bonds. This energy that is released can then break more of the weak bonds and so on and so on. But also remember that an explosion is a rapid expansion of a gas...as hydrogen peroxide decomposes, it releases water and oxygen gas. The rapid production if the gas is what actually makes the explosion. Nitrogen the element is used in explosives not nitrogen gas. A lot of explosvies combine the two factors I just outlined above. Lots of weak bonds are replaced by extremely strong nitrogen-nitrogen triple bonds which releases a lot of energy that speeds up the cleavage of other weak bonds...the side product is also nitrogen gas that then expands rapidly giving you the explosion. Azide (N3-, N-=N+=N-) used to be used in airbags. On impact, the azide decomposes to release lots of nitrogen gas that fills the air bag.
  17. Yes it is a sweeping generalisation...and to a good approximation it is perfectly true. I don't have the space (or time) to to go through every single pesticide used say whether they are good or bad. That statement was based on several papers I've read in the past about organic pesticides being generally worse than synthetic ones; I shall try find them again. And of course there are a whole range of synthetic ones that are just as damaging, I never said that they weren't. DDT (and the majority of its analogues) have had disaterous effects on wildlife; especially to the avian populations in the America's.
  18. I would explain that observation in a different manor. I would say that water is not a strong enough acid to protonate the carboxylate (i.e. the carboxylate is more stable than the resulting hydroxide ion would be).
  19. Specifficaly this refers to a Bronsted acid (there are other tyoes of acids e.g. Lewis acids). A Bronstead acid is defined as a species that donates a proton while a Bronstead base is a species that accepts a proton. But remember, once you have deprotonated your acid, it will become negatively charged and will therefore want to take a proton of somewhere (i.e. it is now behaving as a base). For example: HCl- + H2O <==> Cl- + H3O+ Bronstead acid; Bronstead base; Conjugate base; Conjugate acid Here, the HCl is acting as a baseacid...but once it have reacted with the water, the chloride ion left will them want to act as a base to move the equilibrium backwards. Essentially, the roles are reveresed.
  20. Ok...erm, let me have a think about this then...if you haven't learnt about those simple topics yet, then this problem has just got a lot harder. By the sounds of it, you are just starting at chemistry...so it might be that you are expected to use chemical reactions that are taught to you at the begininning but never use because they are totally useless.
  21. Firstly, I'm sure the teachers know how hard it is...thats kinda the point! Currently, a lot of new ideas that are favoured are based around sustainability and greener energy. Something like that might be a good one. If not, then maybe something about new drugs.
  22. First of all, this seems to be rather a hard problem given your lack of carbon based units! For 3-methyl-but-1-ene, start from ethanol think mild oxidations, grignard reactions, enolate reactions, oxidations and eliminations. For 2,3-dimethylbutane i have come up with a route to do. Starting from ethanol think mild (HINT!) oxidation reactions, enolate reactions and grignard reactions.
  23. There are a number of anti-cancer drugs that specifically target certain region of the DNA. For example, Brostalicin specfically targets AT tich sequences to where it binds....so maybe if you could talour a molecule to bind specially to a certain base sequence in the DNA, then you could target specific people. The problem would be that since the DNA code is so long, the chances of there being a sequences similar enough to confuse the toxin in an unrelated characteristic is very high
  24. You can also think of it that fluorine forms very strong bonds (again related to its size). The H-F bond is much stronger than the H-Cl which is stronger then H-Br which is stronger than H-I....thats another way to look at it.
  25. Do you want to keep both components? And I am also assuming you mean urea as in (NH2)2CO and not a generic urea compound. If you have a mixture of them in water, then you could add saturated sodium carbonate to your mixture. This would deprotonate the formic acid to give the sodium salt. You could then extract the moxture with an organic solvent say ethyl acetate or dichloromethan. You might have to do this a fair few times to get off the urea out but it should be possible....the formic acid salt will not dissolve in the organic layer at all so you will have seperated them. If you then wanted the formic acid as well, you would then simply need to acidify the aqueous washes to get it back as a solution in water.
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