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Everything posted by Kaeroll

  1. In brief: yes. The energy change of a reaction depends only on the start and end points, not the route taken. Going from A to B (under the same conditions) has the same energy change regardless of the route taken. Going from B to A has the equal and opposite energy change regardless of the route taken. Think of it this way: if A -> B is exothermic, B must be in a lower energy state than A. For B -> A to be exothermic too, B would have to be higher energy than A. All else being equal, this is just not possible.
  2. Given that I watched it with my dad who snored through it, I think I can offer an unbiased opinion. I thoroughly enjoyed it, didn't really feel like Sherlock Holmes, but it was smart enough without being convoluted, and the action was of course top-notch. The highlight was definitely Holmes' analytical boxing. (Watch it, you'll see what I mean.)
  3. Fair point. As a chemist I view it as very unusual and interesting - we actually know comparatively little about water and some of the research being done is quite fascinating. I don't know much about it, unfortunately. Liquid oxygen has some fun properties. If you want more to go more complex, a modern area of interest is molecular machinery - atomic scale analogues of macroscopic machines such as pistons and rotors, triggered by stimuli such as pH changes.
  4. For 15,16,17 look up the Sharpless asymmetric dihydroxylation. Not sure about 18 through 20 at this hour of the morning (not had my coffee yet...) but look up asymmetric hydrogenation methods for 18.
  5. Water? Compare it to the other group 16 analogues and its properties are very unusual indeed. For example, it's one of the only (or possibly the only?) compounds that expands when cooled.
  6. I'm going to go only from compounds I've handled personally, largely quite benign. So... Hydrogen sulfide? More toxic than HCN and doesn't smell half as pleasant. Or thionyl chloride: not sure how nasty it actually is but its vapours turned my needles and seals black so I'll avoid that one, ta.
  7. Yup... kinetic isotope effect. Quite interesting actually. Put briefly, D is twice as heavy as H, and forms stronger bonds, leading to slower kinetics (typically about 7-8 times slower for a primary effect). As many enzymes shunt protons about for a living, large amounts of heavy water can really cock things up.
  8. Yes, but it's not that simple. Probably the simplest kind of "displacement" reaction you might consider is SN2 - bimolecular nucleophilic substitution. I've neither the time nor inclination to give a full discussion of this reaction here, but two key properties you might consider (when predicting if this reaction would occur) are steric properties of the nucleophile and electrophile, and the 'quality' (for lack of a better term) of leaving groups in the electrophile compared to the nucleophile. A thiol displacing a bromide ion would be an example of an element of lower electronegativity displacing one of higher electronegativity, but other factors are much more important - pKas, hard/soft acid base theory, steric effects, etc.
  9. Acid + alcohol is a pretty crap way to make an ester generally speaking. Usually needs a much stronger acid catalyst than can be provided by the acid alone, making it more dangerous and less pleasant. It also usually requires reflux for a few hours. I really don't suggest boiling up vinegar in your kitchen! For what it's worth nobody really uses this method (the Fischer esterification) anymore. Plenty of other methods about, though I've never tried one myself.
  10. Put briefly: what effect would the use of a full molar equivalent of catalyst have on a reaction, broadly speaking? One the great advantages of catalysis is that the catalyst only has to be used in a small amount. I'm intrigued as to what effect the use of a full equivalent would have on a reaction - particularly with regard to metal catalysts rather than acid/base or organic catalysts, which would presumably undergo more conventional reactivity at higher concentrations.
  11. There's a nice one called Creations of Fire which, while not technical in the least, gives nice detail on the people and cultures that fuelled the evolution of chemistry. I found its treatment of modern developments lacking but it goes into plenty of depth about the chemical revolution.
  12. Indeed... there's a group in my university working on it, the head of which showed me a summary of the past half-century of work in the area. It was a while back and I don't have a copy unfortunately, but it showed (amongst other things) that it is possible to stereoselectively form all the RNA nucleosides stereoselectively from "first principles", as it were (i.e. inorganic matter, such as phosphate, ammonia, etc). Current work focuses on self-assembly of RNA oligomers and the like.
  13. Nice guide, GDG. Rep + The rules for R/S are known as the Cahn-Ingold-Prelog rules and are used habitually by chemists. Much nicer than the empirically derived D/L system. The R/S tags derive from the Latin rectus and sinister, meaning right and left. The first years I tutor found it helpful to remember that S is anticlockwise, as you draw the letter S in an anticlockwise direction. More detail on the CIP rules can be found in pretty much any undergrad chemistry text; if your library has a copy of Clayden, Greeves, Warren and Wothers' organic text it's usually quite thorough on such things. As for an introductory biochemistry text I'm not too sure, but if you're taking biochem courses, Berg (et al) is quite accessible albeit a little challenging.
  14. Mateusz is correct in saying that the two interconvert via the open chain form. You can follow the formation and decomposition of the ring form using some simple carbonyl chemistry.
  15. I second that recommendation of Berg. My edition has nice explanations, lots of context, and big pretty pictures!
  16. Kaeroll


    Out of curiosity, who are said friends and what are their objections? (Curiosity. Honest. Not part of a great scientific conspiracy to silence those who disagree with thermodynamics. Shh.)
  17. Research into abiogenesis is often termed "prebiotic chemistry". I know at least one group working in my department that uses this term and works with an international group studying RNA formation.
  18. Yeah, that was the distinction I was trying to make. I think it's dependant upon the mechanism rather than the apparent overall reaction, but I'm not sure. I'll have a gander in my textbook and see what Prof Clayden has to say...
  19. Yes, that's the kind of example we were given, and was described as -dig when the mechanism is actually -trig. Go figure. Baldwin's rules are something I had to look up myself - they've popped up a lot this semester and last (during topics on radical reactions, pericyclic reactions, heterocyclic synthesis - where iodoetherification came up - and others) but they've never been formally presented to us.
  20. That's the fundamental question of chemistry, in a way - how can we turn A to B, and what can we predict about B in advance? As hermanntrude said, if you want a complete answer, take a course in chemistry and be prepared for years (a lifetime, if you're willing) of enjoyable study.
  21. That's pretty much my response too. I'm not a great mathematician, so much of physical chemistry eludes me. This semester for example, amongst other things we covered the Eyring equation and its derivation. I was a bit lost. It's still possible to pass a degree (and pass it well) without grasping maths, if you work hard and have an aptitude for synthetic and qualitative aspects of chemistry.
  22. Thanks for your reply and apologies for the delay in mine - it's crunch time yet again. I spoke with my organic tutor about this and he suggested the same kind of mechanism as you. It's a shame it's nowhere to be found in the texts I have to hand (including one for the course this came up in). Just to make things simpler, the lecturer described the cyclisation (which was onto an alkyne, rathr than alkene) as 5-endo-dig, rather than accounting for the likelihood of this mechanism (which would be -trig, presumably). He also offered no explanation for the presence of iodine in the product. Thanks again for your response. It does seem obvious now it's right before my eyes.
  23. My view (and it is just that... I don't claim any truth or evidence for this viewpoint) is that randomness exists to a point. The probabalistic nature of QM suggests it does. So to answer the scenario posited by 'the guy': If we made an ensemble of babies in boxes to find the average behaviour over an effectively infinite number of identical babies, I think you'd find different behaviours with different probabilities, determined by the mass of complex interactions at the atomic (and sub-atomic) level - which are random but guided.
  24. Hi, A synthesis my lecturer dubbed 'iodoetherification' cropped up this week. I can't find reference to it or anything much like it in my organic text; can anyone recommend a book or article with a decent explanation of it? Cheers Kaeroll
  25. Thanks for your reply, that clarifies things a lot. How would you suggest I use the R-squared value in discussing my results? Is it fairly typical to refer to it as R-squared without elaboration? (The project is not based on math or statistics at all.)
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