Jump to content # ChemSiddiqui

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## Everything posted by ChemSiddiqui

1. Hello everyone, I am trying to teach myself theoretical chemsitry and have done well so far. I am using this book called Modern Quantum Chemistry by Szabo. I was reading about Couloumb and Exchange opertaor and I have a question. I understand why Coloumb and exchange operator integrals arise, due to electrostatic potential and antisymmetry of the slater determinant. Then there was this exercise which made me pause. It asks to prove that the coulomb operator denoted by Jii and the exchange operator denoted by Kii are equal. Now in Chemists notation it the couloub integral Jab is given
2. Hi everyone, I am a beginner in the field of laser science and I have been reading a few things about techniques like velocity mapping and charged particle imaging. I understand most of it, but there are certain terms/words that needs clarification. I am going to point them out and explain what I understand from then if any of you can explain if i am correct then please say so and if i am not, please correct me. Ok so first: " In the case of neutral atoms, radicals or molecules, a quantum-state-specific resonance enhanced multi-photon ionisation (REMPI) scheme is generally used to pro
3. Hey everyone, OK i am a bit stuck. I am doing some excercises on graphs and here is this table that contains data to plot a graph to determine the activation energy T/K---------------------------- $10^{13} k / cm^3 molecule^{-1} s^{-1}$ 300----------------------------1.04 350----------------------------1.87 400----------------------------3.04 450----------------------------4.60 500----------------------------6.58 I have constructed an arrhenius plot( ln(k) vs 1/T) from this data using excel. I am getting a slope of -1379. using ln(k) =ln(A
4. Hey everyone, I am a little stuck with some bit of thermodynamics. Basically, I am doing some questions and the first was what expression is equivalent to the partial derivative $(dV/dT)p$. I took the cross-derivative of the equation for free gibs energy ($dG =VdP -SdT$) and got $-(dS/dP)T$. Now this is where I am stuck. the next question says to work out an expression for deltaS as a function of pressure using the expression that I just found. I dont know what $-(dS/dP)T$ is equal to, so my question is that can I intergrate a partial d
5. well when you say lattice strucutre, what you actually mean is a very ordered and arranged structue. spin-lattice relaxation (T1) is in NMR, and i think here 'lattice' refers to the liquid molecules in the solution that are tumbing together. spin is an intrinsic property of electron due to them having spin angualr momentum (denoted by ms), its not really spin spin, but electrons behave as if they are spinning. Environment is what is around the molecule in question. Hope I have helped. Feel free to correct me if I am wrong anywhere.
6. Hi there, try group theory. A good book for this is in introduction to molecular symmetry and group theory by A.vincent. It should answer most of your questions above, or simply punch group theory into google. good luck.
7. Hello Everyone, I was just wondering if it is possible to hypnotise somebody? Has anyone here ever been hypnotised? share you experiences, opinions here....
8. Hi everyone, I was just wondering, because I did this experiment in which we had to oxidise 2-methoxyphenol to get vanillin. Use use nitrobenzene rather than any other common oxidising agent like potassium permanganate etc. I was wondering what that was? Could it be that oxidising agents like potassium permangante need to be acidified and this can dehydrate the hydroxy group on the 2-methoxyphenol and so we dont get the desired product? I am just curiuos!. Your suggestions are appreciated!
9. for future reference grignard reagents usually are used if a carbon-carbon bond formation is involved, but of course the conditions are important in choice of reagents!
10. ## How do you find electronegativity of an element?

As insane_alien said one can calculate electronegativity. there are scales of electronegativity and of them all (3 i think) paulings scale is most commly used by chemists but it is just qualitative, and the numbers are supposed from a scale of 1-4. But allens, mulikkens etc have mathematical expressions with which it is possible to calculate the electronegativity and they are in good agreement to the paulings scale of electronegtivities.
11. Thanks a lot timo (didnt you use to have a different username before? how can one change it?). I used the right units this timeand got a value of n=4 and I can work out the states myself now. good day!
12. hmm....Ok!. I just did the calculation and the result seems a little absurd. Here goes; $E= 5.448 X 10^-(19) J; n=?; R=1.0967 X 10^7 m^-1; Z=1 for H atom$ $n^2 = \frac{RZ^2}{E} => n = 4.48 X 10^12.$ what have I done wrong here? can you let me know? Thanks
13. do you mean $En = -R \frac{Z^2}{n^2}$? but then the question gives a positive value of ionisation energy and with this expression we cant get the value of n as the underoot will be complex. I think if we used the first equation in my previous post such that to set ny = infinity and then from there we can work out nx? what you say to that? thanks for your help though!
14. Hey everyone, I was going through some past exam papers and this question came up and I am as the title says stuck. here goes the problem; what states of hydrogen atom have an ionisation energy of 5.448 x 10^(-19) J? This question requires students to do some mathematical calculations. I was wondering if can I use the formulea $Enx-Eny = hcR (\frac{1}{nx^2} - \frac {1}{ny^2})$ and then apply $En = - \frac {hcR}{n^2}$ (where R is the rydberg constant) to get n and work out the quantum numbers from there? any help most appreciated. thanks
15. hi there everyone, I just drew a mo diagram of c2(C=C) and see that the bond between the two carbons is a double bond and that is due to the 2p pi orbitals. so where does the lone pair come from in the dicarbon then? I reckon they come from 2s bonding and antibonding orbitals. frstly could anyone confirm that please. given that, the dinitrogen has a similar mo diagram. comparing the two, can we say that the lone pair in dinitrogen have the same energy as in dicarbon as they too come from the 2s bonding and antibonding mo'? any comment or help appreciated.
16. Hey everyone, I was just wondering if a piece of graphite that has 60 carbon atoms can form a closed polyherdral structure? I think that the key to answering the this is using eulers forumla but I dont know how to use it. this is as much I can do; V + F = E + 2 60 C atoms divided by 5(for vertices of pentagon) will give 12 pentagons. 12 pentagons make 60 vertices. 5 hexagons can be linked to a petagon to give a closed structre and each heaxagon is then linked to 3 pentagons and three hexagons. I cant go further than this. Any help much appreciated. thanks.
17. Hey everyone, I was doing some past papers and this question (see below) came up. I am not sure If my answer is correct or not, but maybe you can comment on it and tell me. Is [Hg2]2+ stable towards disproportionation? +0.91 +0.77 Hg^2+ ----------> [Hg2]^2+ ------------> Hg I would say that the [Hg2]2+ is not stable towards disproportionation as the the potentail to the right of species [Hg2]2+ on the latimer diagram is lower than the potential on the left of species. Do you think that this is right approach (qualitatively)
18. Hey everyone, Its been a longtime since I last logged in and I couldnt wish the fellow SFN members a Merry Christmas so I am doing it now with apologies :Merry Christmas and a Happy New year. ChemSiddiqui
19. I was wondering that if we used con.sulphuric acid on the endo-norbornen-cis-5,6-dicarboxylic acid, would it undergo dehydration? Is it even possible at all? any comments are appreciated.
20. you mean calculating deltaG using the E values? well if there is no chemistry of phosphorus with water then it would be useless to try getting the deltaG dont you think? I was searching that on the internet and this is what caught my attention and looks like phosphorus does react with steam and makes phosporus acid; http://www.freepatentsonline.com/2706146.pdf
21. I was just wondering if phosphoruous can react with steam? I know it has no chemistry with water but I reckon that it might react with steam in gaseous state/form i.e. P(g) What you guys think? throw in your idea, comments etc they are welcome.
22. ## 1H NMR & IR : unknown structure determination

what are diagnostic bands used to interpret IR? try looking for strecthing frequencies of the functional groups that are in your proposed structure.
23. Thanks aeontde for that but that is what I already know. I merely wanted opinion on the geometry, because in this complex vanadium can adopt the 5 or 6 coordination. but anyway, you are right acac- do have the aromatic character. I got the bond length data and similar bond lengths suggest delocalisiation. thanks again.
24. Hey everyone, I was just wondering in the VO(acac)2 which is a Vandium (IV) complex the V=O bond length is significantly shorter than V-O bond length so the discription that it has a square-pyramidal geometry is somewhat misleading. what do you guys thing? I know that in books and at various places it is stated to be square-pyramidal. I am also suspecting some distortion because of the Jahn-teller effect? your opinion on that is welcome. PS. I just realised I said Jahn-teller distortion which is obviuosly not possible for this complex.
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