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Everything posted by Tartaglia

  1. Thiophenes react with electrophiles to substitute at the 2 position, with relatively little at the 3 position. This means direct substitution with eg trimthylsilyl chloride on thiophene will not be a suitable prep. You may have to ring close a suitable diketone with P2S5. You might also start with 3 bromothiophene (http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv5p0149) which you could react with lithium and then TMSCl.
  2. cis - but-2- ene has C2V symmetry so will have a small dipole moment due to the methyl groups slight positive inductive effect cis but-2-enedioic acid will form an intramolecular hydrogen bond forming a 7 membered ring. There are a number of effects here which will determine which oxygen participates in the hydrogen bond. These include hybridisation of the lone pair orbital, ring strain, eclipsing cost, cost of twisting the conjugated system out of allignment and doubtless other effects too
  3. I think this can probably be explained by a combination of steric, electronic and entropic effects, but there is a lot of competing effects here. 1,4 Micheal addition is certainly favoured by soft nucleophiles such as thiols, but the methyl on the quarternary carbon will probably hinder attack from above and the other ring will probably hinder attack from below. The same methyl also hinders 1,2 attack at the simple ketone. Ring closure is certainly going to be favoured by the second law of thermodynamics as there is another water molecule eliminated. The use of a 1,2 diol to attack the simple ketone is probably electronically driven as I am reasonably sure the alpha beta unsaturated ketone is less favourably inclined to 1,2 attack by hard nucleophiles than a simple ketone. ( I can at least partially justify this to myself by drawing other resonant forms.) Also oxygen is considerably smaller than sulphur and so steric hinderance may be less of a problem. Hope this helps
  4. Convert it to an ester first and NaBH4 will work
  5. Promotion of an s to d occurs when the increase in spin exchange energy exceeds the pairing energy, but this is a very small part of the picture
  6. For time series there are all sorts of statistical tests for all sorts of non randomness whether it be cyclic, autocorrelation, no of turning points, unit roots etc etc
  7. If you study chemistry at university you will study group theory and molecular orbital theory and all will become clear. It is a little difficult to explain but aromatic systems with 4n+2 pi electrons delocalise, whereas those with 4n pi electrons are localised
  8. The test required here is a test on the fourier transform of the data. The second will be massively significant.
  9. It is safer and more usual to isolate NO+ as a BF4- or a PF6- salt as perchlorates are explosive. I use to use NO+ salts occasionally to produce M-NO complexes. They are very interesting as the NO ligand can act as a 3e donor or a 1e donor and so have always been of interest to those studying catalytic mechanisms. NO+ salts are both air sensitive and moisture sensitive as the NO+ cation is both oxidising and reducing
  10. A model of the form ln(p/(1-p)) = a +bx +e p = proportion/probability a = intercept b = gradient e = error term x is the independent variable a and b are fitted to minimise errors The model can be used with more than one variable too
  11. Some d0 complexes are actually coloured eg TiCl4(thf)2 is vividly yellow. Obviously it is not a d-d transition causing this, but there probably are other transtions as well invoving ligands. Another problem with assigning colours to transition metals in these situations is that a minisule amount of any impurity with a metal ligand charge transfer band can give rise to a significant colour. Charge transfer bands have much higher extinction coefficients than plain d-d transitions which are actually quantum mechanically forbidden but become weakly allowed if symmetry is lowered
  12. The valency of d block metals depends on a lot of factors including Successive ionisation energy, Strength of ligand, Whether the ligand is a pi donor Whether the ligand is a pi acceptor Possible resonance in pi based ligands symmetry (group theory is a big topic in degree chemistry) whether the complex is high spin or low spin crystal field stabilisation energy pairing energy lattice energy (for solids) solvation energy for solvated ions, covalent metal-ligand bond strength ete etc etc
  13. I think a little lesson in the meaning of azeotropic and eutectic is needed here. They do not apply to single states they apply to changes of states. Eutectic applies to solid/liquid change of state and azeotropic to the gas/liquid change of state. Thus Borek is right both azeotropic and eutectic apply to liquids mixtures as liquids both freeze and boil
  14. Ethanoic acid and water form a eutectic mixture
  15. Dark photon - I'm guessing you are GCSE age, so some of the following you may need to look up. I guess this is the acidic decomposition of the thiosulphate ion which is first order with respect to conc of thiosulphate This means the rate = k*[s2O32-], where k is the rate constant. If the conc of H+ remains approximately constant during the reaction ie [H+] >> [s2O32-] then the expression required is [s2o32-] = A*exp(-k*t), where A = initial conc of S2O32- This actually quite a complex reaction rate problem as at low conc of H+ it is first order wrt [H+] and at higher concentrations it is zero order wrt [H+], which makes it similar to many enzyme reactions
  16. at ph 10 edta is a 4 negative ion and can act as a hexadentate ligand with the two amine groups and the four carboxylate ions acting as e- pair donors. If edta were added unbuffered it would be some sort of zwitterion or possibly a dizwitterion. This would block hexadentate coordination and probably lead to formation of polymeric metal ligand metal ligand chains, or possibly little coordination as the entropy consideration will be a lot less favourable
  17. Martin Politics interests me at least as much as mathematics and science. I was unaware that he actually joined in 1937 but I would imagine he was a fellow traveller before then. I really did not mean to stir up a hornets nest, I was just putting the information in as an interesting aside. Obviously it caught your interest if not Swansont's
  18. Swansont - I tend not to compartmentalise my knowledge and I was not making any suggestion that Haldane's scientific contributions would have been different had he been a capitalist. That neither of us can know. What I do know is that Haldane was not only one of most important scientists of the 20th century and one of its most successful popularisers of science. Many of his famous essays appeared first in his column in "The Daily Worker" and in the period he was writing many intellectualy gifted people were attracted by both science and communism. Indeed I was once privileged to meet John Maynard Smith, who did his PhD for Haldane while moving through the CPGB. He ofcourse made important contributions to evolutionary biology himself. On a personal note, although Haldane died the year I was born, he had a great effect on my career. About a week after I was appointed to my first University lectureship (age 25) a friend of mine who was appointed on the same day as me gave me Haldane's book of essays "On being the Right Size". This led me on to Ronald Fisher's work and ultimately I became a statistician. For me it was one of those pivotal moments.
  19. Not at all Swansont, but if you read the essay (written 1928) you need to know the context in which it is written to understand the references to socialism. Thus the mention of his affiliation is not irrelevant. Perhaps you should read the whole essay before you put up ill advised posts J. B. S. Haldane was one of the great characters of science and a true original. He was rather more famous as a public face of the CPGB at the time though
  20. Here is one of the most famous scientific essays is on this subject "On being the right Size" by J. B. S. Haldane, the great British mathematical biologist and Communist party member http://irl.cs.ucla.edu/papers/right-size.html
  21. Atheist, Nuclear Magnetic Resonance spectroscopy is a technique used extensively in synthetic chemistry. It is usually used in identifying different chemical environments of spin 1/2 nuclei (mainly, 1H, 13C, 31P) when microwaves are aborbed when a magnetic field is applied to a dilute solution of the chemical. The precession of the magnetic moment of the spin is reversed on photon absorption. It is no exageration to say that when the technique was first introduced into chemistry (ca 1961) it completely revolutionised organic and inorganic synthetic chemistry
  22. Good luck anyway - I remember doing my PhD, loads of work no money, no responsibilities. Time of my life!
  23. Yes Ecoli, Nuclear Magnetic Imaging is a much more recent application I remember using an old continuous wave machine in 1983 that was almost 20 years old
  24. The problem with general explanations on this theme is you need to draw a lot of diagrams and thats not easy in this format. Come up with something specific and I'll gladly help
  25. Possibly the best thing you could do is scan a few questions into a file and stick them up here. There are so many subtleties to nmr I could put up a load of stuff and still not really cover what you want.
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