 Once again, welcome you all to MSP lecture series on interpretative spectroscopy. In the last couple of lectures, I was discussing about multi-nuclear NMR. In the beginning, I gave more emphasis for phosphorus 31 NMR and also in between I brought other nucleus such as 14 N, 15 N, 19 N. So let me continue from where I had stopped. Let us look into another interesting example. Let us look into the problem shown here. Interpret the spectrum below for the compound, methyl group is there, platinum ethylene is there and two dimethyl phenyl phosphine ligands are there. So justify all splittings is this the cis or trans isomer and the data given is 31 P, 100 percent abundance I equals half and of course 195 platinum is NMR active with I equals half and 34 percent abundance is there and then 196 platinum is 66 percent and that is NMR inactive I equals 0. So with this information and here information is not given about the spectrum shown here which spectrum it is. So by looking into the spectrum and also by writing all possible isomers for this compound we should decide whether it is cis or trans if that is the case which NMR this spectrum represents. So let me first write this one. So platinum I can write P, PH, ME2 this ethylene. So other possibilities so these two possibilities are there and if you consider this trans isomer. So in this case both the phosphorus environments are identical because one can perform C2 axis of rotation in this direction along with the ethylene platinum CH3 axis whereas here I do not think we can perform C2 axis C2 rotation in this direction or in this direction and to make two phosphorus mites equivalent. So if you consider this one and now we have to see what nuclei NMR this figure given here the spectrum represents. Now if we look into phosphorus now phosphorus whether we take this one we have two mites then we should have PP coupling should be there. So then it should appear as a doublet of doublet. So that is not there the pattern does not look like it belongs to this kind of spectrum if it is phosphorus NMR and if it is platinum NMR again and this will couple with first a doublet and then doublet again it should be doublet of doublet and there is a possibility of coupling with long range or two bond platinum to hydrogen coupling. Then that would be some sort of satellites or if you take platinum then it should be doublet of doublet of triplets or quadrates that is not there. The other option left is now one HNMR if we take one HNMR we can identify three different type of environments apart from phenyl region. One is methyl groups are there here and then we have CH3 is there and then CH2 is there and if we exclude phenyl region then we will come across three different type of environments one is for ethylene protons one is for methyl and other one is for again methyl groups present on phosphorus. If we just see that one one HNMR if we take and this would couple this ethylene protons will couple equally with the two phosphorus to give a triplet and then each triplet will be having a satellite appears like a doublet triplet of doublets and that is the case in this one. For example, if it splits into triplet this I am writing for ethylene protons and then because of platinum coupling we will see something like this coming here and then here we have so this is one set and then if you look into CH3 proton again CH3 also same case is there but CH3 protons will be split by two identical phosphorus into a triplet and then they are further split by platinum to showing platinum satellites here. It is also identical to what I have drawn here and when we look into this six protons here and six protons here they are quite similar as a result these 12 protons are there so they split by again phosphorus into triplet and then again platinum is split them into doublet that means we can anticipate three sets of individual separate triplets in this case if it is one HNMR and then they will be having corresponding platinum satellites that is what the spectrum looks like now and you can see that expanded version here one is at minus 1.10 ppm and minus other one is minus 41.2 ppm and other one is 0.083 ppm so that means without any problem we can say that this is for CH3 and this is for methyl groups on phosphorus and this is for ethylene hydrogen atoms so this one and then we can say that this is one HNMR spectrum of this trans phosphorus containing ethylene containing methyl group containing platinum compound and then this whatever we see here these are all platinum to hydrogen couplings they come as satellites here. So this spectrum is for one HNMR and it shows for ethylene a triplet and satellites and again methyl group a triplet because of two equivalent phosphorus splitting that into triplet and again satellites and again methyl groups satellites. So no doubt this is one HNMR spectrum so this how one can analyze and interpret the data so let us move on to other examples here. So now let us come back to lithium, lithium we have two isotopes are there six lithium with I equals one and 7.4 percent abundance and then other one is 7 lithium with I equals 3 by 2 and natural abundance is 92.6 percent. One should remember the fact that those nuclei with I greater than half are quadrupolar and since 6 li has lower quadrupolar moment and yields sharp signals but has low sensitivity however in case of 7 lithium is highly sensitive but has a higher quadrupolar moment. So its signals are always broader and then when we look into chemical shift range whether you consider 7 lithium NMR or 6 lithium NMR the range is very similar for both the nuclei. You can see here lithium amide in ammonia it comes in this range and then external paratropic contact ions will be in this range and aqueous lithium plus would be around zero and solvent separated allions also comes in the same range and external diatropic aromatic contact ions would also come here and alkyl lithium would come around here and sand which should diatropic aromatic contact ions would come anywhere between minus 10 to 15 and also lithium plus ion in ammonia comes around minus 10. So now I have given here for LICL taken in D2O with natural abundance in case of 6 lithium it comes here as expected it will be a singlet. Similarly one can also plot 7 lithium NMR for LICL in D2O this also is sharp singlet you can see here and here I aqueous 3 by 2 but it does not matter here it is I aqueous 1 here this would come only when we are seeing lithium is coupled to other NMR active nuclei. So now you can see here spectra are given for 6 lithium and then these are not simple lithium compounds that deuterium induced isotropic fingerprints in 6 lithium NMR spectra of partially deuterated argonolithium aggregates that is the reason they look not simple phenylithium monomer is there here because of interaction of pi electrons of the carbon that is binds to lithium they will be having a dimeric structure something like this and of course when you take methyl lithium or any alkyl lithium, tercibutyl lithium or methyl lithium they will be having cuban type structure with this relationship would be like tetrahedral and in this one each methyl group the lithium is coupled with CH3 protons to give a 1 is to 3 is to 3 is to 1 triplet and here they are coupled with methylene protons here and of course it is not easy to interpret it looks like it is coupled to 2 hydrogen atoms as a result it is showing a triplet because this are all partially deuterated you never know how many CH2 are there whether CHD and all those things but from spectrum it appears that it is coupled with two equivalent hydrogen atoms as a result it shows 1 is to 2 is to 1 triplet whereas here it is very clear methyl hydrogen atoms are coupled with lithium to show quadrate 1 is to 3 is to 3 is to 1 and here one such lithium reaction is shown here this was carried out in our group here what happens the lithiation is very sensitive to temperature and also if other acidic protons are there you can expect the possibility of lithium exchange although we replace with halogen exchange process for example this bromo compound is taken and when it is treated with n-butyl lithium at minus 78 degrees celsius and then at the same temperature if you add chloride ifenyl phosphine of lithiation it gives here exocyclic ortho position here PPS2 is added and it gives a compound like this but on the other hand after adding n-butyl lithium at minus 78 degrees celsius it initially formed this one and in case if it is warm to room temperature for the addition of fluorine and phosphine what happens the moment it is warm above minus 78 that means when it starts warming up and attaining zero degree centigrade are coming to room temperature what happened lithium exchange takes place with this one and then lithium will move here and H will move here and then if we add chloride ifenyl phosphine so it goes to trizolic carbon that means basically this one has to be extremely careful while doing lithium reactions they are very very sensitive to temperature and if you have some acidic protons in the nearby where lithium is occupying on the carbon there can be exchange process and this is one such example where temperature assisted lithium hydrogen exchange takes place is it possible to monitor this one yes it can be monitored by looking into seven lithium NMR spectrum here so we carried out time dependent seven lithium NMR spectra and a series of spectra shown here immediately after the addition of N butyl lithium what happens it goes through halogen exchange to ortho carbon and with the time you can see here after six minutes what happens another signal is developing towards the right side that means lithium hydrogen exchange has started and by the time the time attains one hour fifteen minutes complete exchange takes place and it's no longer lithium is no longer present on phenyl ortho position it has moved to trizolic carbon so this indicates sometime this kind of variable temperature assists in understanding how this process is taking place why I expected a phosphination at ortho position whereas I got phosphination on trizolic carbon so all this vital information one can extract from doing variable temperature NMR studies not necessarily with lithium with any other NMR active nuclei provided gives a clue about such reactions okay so now let us look into another interesting aspect isomerization if you just look into this compound here it's a multi-dentate ligand and of course the most favored are pp chelation but on the other hand we have also have this trizolic nitrogen atoms with a pair of electrons on each one so they can also coordinate so here when this compound is treated with tetra carbonyl this bipyridine tungsten compound at room temperature initially pn coordination takes place and keeping this in solution for 72 hours it undergoes isomerization from pn coordination to pp coordination and the other hand if you take the same bisphosphine and add malbedenum here whether it's malbeden or tungsten both this isomeration happens but only in case of tungsten it takes 72 hours whereas in case of malbedenum within two minutes pn burning compound takes place on storing for two hours within two hours isomeration completes and it comes to pp coordinated compound so that means again here whether it is possible to monitor isomerization process that means ligand being pn coordinated initially to become pp coordinated one yes one can do it I will show you here and this is for the isomerization of pn coordination to pp coordination on malbedenum and if you take it initially you can see two signals are there two signals can be seen for both uncoordinated phosphorus atoms since this compound here both the phosphorus atoms are chemical and magnetically non-equivalent and they are further from each other as a result you are not seeing any pp coupling but nevertheless they show two chemical shifts that you can see here and once after adding malbedenum complex to this one coordination starts and immediately you can see only one peak is there other one is coming somewhere here coordinated that means basically what happens one of the phosphorus is left uncoordinated and whereas one of the phosphorus is coordinating so you can see that means here we have a complex where we have pn coordination since pn coordination is there other phosphorus centrizole carbon is left uncoordinated and that is here only uncoordinated region little bit shift is there compared to this one and then with the time you can see now another signal is developing here these two are for coordinated pp coordinated compound here with the time it is increasing and you can see but two hours within 120 minutes this isomerization completes and then this is disappearing here this one is uncoordinated one present on this one this is disappearing and after two hours you can see completely pp coordination and we do not have any trace of pn coordinated compound so that means we know now isomerization from pn to pp takes roughly two hours and whereas in case of tungsten it is taking little more time so you can see here to begin with again very similar to malbdom complex it's uncoordinated both are here within one hour what happens one of the trizole carbon remains uncoordinated whereas the other one is getting coordinated as a result what happens the pp coordinated compound pn coordinated compound is there and then with the time what happens this is decreasing and then it nearly takes 72 hours for the completion of isomerization from pn to pp here and another advantage with tungsten compound is we can see here these tungsten satellites tungsten is also NMR active and we have very trace quantity here and we are seeing the tungsten satellites and tungsten to phosphorus 1j coupling is about it can vary between 200 to 350 Hertz so this also we can see very nicely the satellites are coming here so that means in case of malbdom it took two hours whereas in case of tungsten it took 72 hours and that can be clearly seen from this time dependent 31 pnmr spectra for the isomerization of complex of tungsten so let me stop here and continue in my next lecture more interesting examples with emphasis on boron mercury and even including 19 fnmr spectra from all these mixed okay nmr nuclei compounds until then have an excellent time and enjoy interpretive spectroscopy course thank you