mississippichem

Could you describe your distillation setup? This could really go very wrong.

Simple. Because it works better than any other form of knowledge collecting with respect to understanding and manipulating the universe.

One, IMO, very convenient thing about the bra-ket notation is the way operators can be expressed: [math] \langle \phi | \hat{A} | \psi \rangle = \sum_{i,j} \langle \phi | i \rangle \langle i | \hat{A} | j \rangle \langle j | \psi \rangle [/math] As I'm sure you know this gets quite ugly if you try to write this out with full wavefunctions. Also things like showing whether or not an operator is hermitian is much cleaner rather than writing out huge integrals. Think [math] \langle \phi | \hat{A} | \psi \rangle = \langle \psi | \hat{A}^{\dagger} | \phi \rangle ^{*} [/math] versus [math] \int_{-\infty}^{\infty} \phi \hat{A} \psi \ \mathrm{d} \tau = \int_{-\infty}^{\infty} \psi \hat{A}^{\dagger} \phi \ \mathrm{d} \tau [/math] You get to use all those convenient bra-ket manipulation rules (remembering a few identities) instead of getting bogged down with all the integration. There is much more to it than that [everything I've shown here is ultimately trivial] and I'm sure someone like ajb can put me to shame here, but these are just some of the wonderful time saving things that you can enjoy with bra-ket notation. The notation looks scary at first indeed. The best way I've found to get a feel for it is to just dive in and try to do some things that you already know how to do in the new notation. The Feynman Lectures volume III have a great introduction on this that is very intuitive and requires minimal vector/tensor formalism.

Point taken. Clearly and strongly argued. I conceed.

Elaborate please. I'm with JohnCuthber. How is the presence of our Earth evidence of any mystical being? Surely you agree with me that natural processes formed the Earth. Why evoke magic?

A quick google search reveals that he spams this stuff all over the internet. He never really seems to answer anyone in a fashion that even remotely follows the question asked of him, so he is either a bot or doesn't know enough English to hold a conversation. kumarevo: Please write out some prose an explain what it is you are talking about. Based on your post history throughout the internet you regularly fail Turing tests. Please show that you have some intent here other than using this site as a billboard on which to post your math-spam. We are a discussion forum, not a free publishing house.

Well in the pure consideration of a single molecule in a vacuum I don't think there is an upper bound to molecular weight. However there are real synthetic limitations. Take for example a simple linear alkane. In theory, though it's not too practical, we can synthesize alkanes of considerable length from methane by a series of radical reactions; each successive reaction having a radical termination step that yields an alkane longer than the last reaction (I know the lengths will really be more of a statistical distribution but we'll not consider that). Eventually we get to the point where we have to apply a lot of energy just to keep the alkanes in the gas phase during the reaction (somewhere around C20H44) so we switch over to solution phase, bring in a Zielger or metallocene type catalyst and starting making polyethylene which is just really high molecular weight alkanes, up to a few million g/mol. Even here we still run into a practical limit though as at some point we don't have a high enough molecular weight liquid solvent to solvate an ever growing polyethylene chain. What I'm getting at is that there is no theoretical limit to the molecular weight of a compound but there are very real practical limits. Interesting, +1.

Are you familiar with the Henderson-Hasselbalch equation? [math] pH=pKa + \log \left ( \frac {[\mathrm{A^{-}}]}{[\mathrm{HA}]} \right ) [/math] So if [math] \mathrm{[A^{-}] \geq [HA] } [/math], then [math] pH \geq pKa [/math] In plain language, if the molar concentration of the conjugate base form of an acid is greater than or equal to the molar concentration of the protonated form then the pH of that acid is greater than it's pKa. The rule you speak of applies in all aqueous solutions [where pH is well defined] if pKa is greater than pH then there will be more of the species in the protonated form. Lidocane's pKa is lower than Prolocain's so Lidocane is more acid. This means that a greater fraction of Lidocane molecules will be in the conjugate base form when compared to the fraction of molecules of Prolocain that are in the conjugate base form in a solution of the same pH.

I tend to be of the combinatorial pessimist crowd. It is my opinion that in order to do combi-chem effectively, your libraries would have to be orders of magnitude bigger than anything anyone has attempted to date. I had a blog entry about this. I never blog really but here it is none the less, The d-blo[g]ck. There you will find my brief synopsis and a link to here were the issue is detailed. In short, the problem is that combinatorial libraries compose such a small portion of the chemical space as to be ineffective. So in essence the process is like trying to map the earth with a microscope, i.e. you can't see enough of the whole at one time to draw any useful information. Now as far as computation goes I am quite the optimist. Of course I have a pretty major bias as I'm involved with computational work . I think the approach of finding a structure that fits a set of predetermined properties is much more realistic than making a load of compounds and hoping that some of them have said properties. It always makes me laugh when you read a great synthesis paper, especially natural products synthesis and the author mentions that this compound might find application in the pharmaceutical industry. Anyone who hopes to be able to scale up a 22-step synthesis producing a compound with five chiral centers and three bridged rings is fooling themselves, given the current state of process chemistry that is. I think that part of the reason that so much of the chemical space is unexplored is the way we do chemistry. No one does a novel synthesis without some form of literature precedent anymore. This is understandable as people do not wish to take risks with their livelihood. Take this compound for example: Bad article with an interesting compound I absolutely abhor the article and what it's about with respect to education but ignore that and look at the structure. This compound is simple right? The symmetry is high. The carbon backbone is not complex. This an example of those inaccessible areas of the chemical space. I can almost guarantee that no one will be able to find a viable synthetic route to it. That is quite interesting but are those not just single atoms and diatomics intercalated onto a metal surface? I see how this type of technology could eventually lead itself to something that resembles atom by atom synthesis though. Nice link, thanks.

I should stress that you DO keep that diazonation mixture cold. Do you stir vigorously during the diazonation? I ran into problems a few years back with cold diazonation mixtures forming gels.

Who knows how such a method might work? We are so far away from anything even similar that any guess as to the engineering that might go into it is pure speculation. Not sure I understand. Atom by atom synthesis wouldn't involve hardly any of the methods we currently use. This sentence doesn't follow your previous ones. No way. We are nowhere near atom by atom synthesis and we don't really know if anything like that will ever be achievable or even desirable/practical. You're really speculating quite intensely without much support. Also, the thread is about the chemical space in particular, though some speculation about future synthetic methods may be relevant.

There is some similarity. Here the limit is the number of realizable bond configurations. It is my opinion that there is a fundamental limit to the number of types of compounds. That number is just incredibly huge. Another more subjective part of what I'm asking is, will it continue to be interesting? Which makes what I'm talking about different than what you mentioned in a way. Atom by atom synthesis may be possible one day in the distant future. Whatever those methods are their limitations are likely to be completely different than the ones we have now. That's an interesting way to look at it though, from the standpoint that future synthetic limitations will be less. But we still have to consider stability. Compounds that have a short (unusable) half-life now will still be just as short lived no matter how finesse our synthetic methods. Will we run out of novel compounds even in the event of ever-better synthetic tools?

When threads are deleted you basically have a chat room. One of the great things about a forum is that your idiocy can be ingrained in the annals of time for billions to gawk at henceforth . Really makes most people think twice before spouting off, some not so much.

Moved to speculations. Please don't post speculative material in the mainstream science forums.

Many people are not familiar with the concept of chemical space. In short, chemical space is the set of all "possible" compounds. The chemical space is quite large. For example, there are about 1029 stable derivatives of n-hexane with 150 substituents or less (1). But one has to consider that the space of compounds that can actually be made by some real synthesis must be much more limited than that. Even further, the number of actual distinct chemical topologies must be even smaller. By topology I mean distinct functionalities that are not redundant. For example, just building longer and longer alkanes is not interesting. My question for the thread is, will organic chemists run out of interesting chemical space to explore? Ever? Perhaps in the distant future? The second part of the question I'll propose is whether or not all the easily accessible functional groups have been found. There will be a degree of subjectivity in anyone's definition of "easily accessible" but I think this can make for an interesting discussion anyway. Your thoughts? (1) Christopher Lipinski; Andrew Hopkins Nature 432, 855-861 2004

It was merely a not funny joke. The thread was about sniffing/ingesting toxic chemical and you brought up coffee so...Once a thread has been "necromanced" they tend to wander and are hard to kill. They behave like zombies. Let's hope this thread dies again after this post.

If the OP can ever figure out which solvent it is he can consult wiki's (only somewhat trusty) table of azeotropes: table of azeotropes I actually used the little known ethanol/toluene azeotrope last week and was saved at least two more hours or rotovaping.

No phosgene with your coffee?

Without any characterization data, it may have worked and you wouldn't know it. OP: what is the substrate you are trying to brominate? What is the solvent etc...

If the process is adiabadic (no heat transferred across the system boundary), and there is no work done on or by the system. The change in enthalpy is zero. Yes. [math] dH=dU+Vdp+pdV [/math]

I damn sure wouldn't want the jarheads to have access to the red button.

Indeed. Queens of Wands/Div. the future...whatever the name was the day she was banned was definitely a case of a poster who had bad intentions. Nothing unfair occurred in my opinion. Like Hypervalent_Iodine said, it was by sheer grace that she was not banned earlier. Multiple accounts of plagairism, and multiple accounts as well as a history of trolling the hell out of other forums lead me to believe that she was the kind of poster that would only bring poor quality threads here. I agree. Though it should be noted that ideas in the speculations forum begin with zero credibility. I assume posters post in good faith. In return the staff should confirm/deny their assertions in good faith which I think is done well here at this site. It is only fair that an idea begin with zero credibility and gain or lose credibility according to its merit. As md says, it is unfortunate that people hold things against posters from other threads, but that is only human. You would have that to an even greater degree in a less moderated forum or to an even greater greater degree in a "real life" setting (think University department drama).

No. Bond forming events are exothermic, [math] \Delta H < 0 [/math]. Bond breaking events are endothermic, [math] \Delta H > 0 [/math]. Try to think of enthalpy in terms of how it changes without respect to time. Instead of saying that the enthalpy increases when a bond is broken, say that bond breaking is an endothermic process. I know it is seems trivial but it isn't. Read into the concept of state function. Also, the energy is not "used up". It is transferred to a molecule from somewhere and can be used to break a bond. Energy is conserved if you count everything in the system and the surroundings (remember energy can either exit or enter the system if our experiment is set up that way, which it usually is in solution chemistry settings).

No problem. Helping you helps me to be a better communicator of scientific knowledge. But yeah, I'm not usually a fan of telling people to memorize (mathematical and or conceptual understanding is FAR superior in every way), but unfortunately there are things like sign conventions that are just best memorized. So as it pains me to say it , just memorize it in any way you see fit. Welsome to SFN by the way.

You've got it backwards. Endothermic reaction have positive enthalpies, exothermic reactions have negative enthalpies. Of course this is all by convention but the convention makes sense as it is in line with the generally accepted physics sig convention for work being done on/by a system. Also, you don't really create bonds with energy. A bond is a lower lying quantum state than the orbitals that comprised either of the orbitals in the atoms that will participate in the bonding. You can think of a bond as a low potential energy state of electrons in a molecule. When the energy of a molecule is lowered by the formation of a bond, the excess heat has to go somewhere, so we observe exothermy. It takes energy for the electrons to climb out of this potential so bond breaking events are endothermic.