 Hello everyone. I welcome you all once again to MSP lecture series on interpretive spectroscopy. This is the 11th lecture in the series. In my previous lecture, I had initiated discussion on 31 PNMR spectroscopy and also I was telling you how simple it is to understand if you decouple, if you have large number of protons or hydrogen atoms and 13C and 31P they can always simplified by irradiating and avoiding interaction of those nuclei with hydrogen atoms so that it is further simplified and interpretation would be very easy. In the same way often we do it in case of phosphorous NMR also and let me now continue from where I had stopped and now let us look into the extensive list of chemical shift range for various groups shown here in the slide and you can see here in case of primary phosphene where we have one alkyl aryl group on phosphorous and two hydrogen atoms are there. The range will be minus 150 to minus 120 that means they are highly shielded and then if you have secondary phosphene where we have two alkyl aryl groups and one hydrogen is there it comes down it will be around minus 100 to 80 ppm and then if you go to tertiary phosphene whether it is alkyl or aryl tertiary phosphene show in the range of minus 60 to minus 10 and in case of secondary phosphene if we have halogens in place of hydrogens so it comes around 80 to 150 so it is slowly moving from shielded to de-shielded region as we are adding more electron with the drawing groups on phosphorous that can be clearly seen from these trends of chemical shifts here and if you take Nr2 groups are there on phosphorous amides in that case it comes to 115 to 130 ppm and if you have phosphates trialkoxy or triaryloxy phosphates we can see the chemical shift coming in the range of 125 to 145 and if O is replaced by yes thio phosphates chemical shift range remains more or less same it is 110 to 120 and if you have trihalophosphines like trichlorophosphine tribromophosphine the chemical shift range is about 120 to 225 and then if you have two aryl oxy groups and then one halogen again it is further comes to down field and around 140 to 190 and then if you have two halogen atoms and phosphorous with one carbon it comes to 160 to 200 and then if you have a combination of carbon halogen and nitrogen it further comes to down field to 165 to 185 and then if you have pentavalent tetra coordinated compounds like Pbocl3 the range is minus 8 to 5 and in case of again we have a combination of halogen and alkoxide or aryl oxide it comes to minus 30 to 15 and then if you consider here the same combination with variation in the halogen and alkoxy or aryl oxy group or groups then it can falls down to minus 20 to 25 and then for a typical phosphate it comes around minus 20 to 0 and then again we can have among pentavalent compounds tetra coordinated one with sulfur P double bond yes it comes in the range of 60 to 75 and then if you have this kind of compound it comes to minus 5 to 7 war group and C it can be alkyde and then we have with war group and yes it comes around 80 to 110 and then in case of this one we have hydroxy groups are there with one carbon it comes in the range of minus 5 to 25 and then here it comes between 0 to 20 and then if you have war group and two CP groups are there and PO and then it comes around 0 to 60 and again two halogens are there and one carbon it comes around 5 to 70 and then halogen and nitrogen it comes around 25 to 50 and then if you have whether PO or PS compound with C3 it comes in the range of 20 to 60 that means thiophosphine oxide or phosphine oxide with tertiary phosphine oxide or tertiary phosphine thioxide they come in the range of 20 to 60 and if you have halogen R2PO CL comes around 40 to 90 and if you have pentacordinated pentavalent phosphorus compounds it comes around minus 75 to minus 5 and if you have phosphonium salt it comes around minus 5 to 30 and if you have vitic reagents they come around 5 to 25 and then if you look into phosphines and trimethyl phosphine shows at minus 62 triethyl phosphine at minus 20 triisopropyl minus 33 triisopropyl is minus normal propyl it is 33 and isopropyl is minus 19.4 and trienbutyl phosphine normal one will be 32 and isopropyl is minus 45.3 and secondary butyl is 7.9 and tertiary butyl is 63. So most of these phosphines we use with palladium or platinum in combination or with rhodium while using them in homogeneous catalysis from that point of view just having some knowledge about their chemistry could be very helpful phosphorus 5 compounds if you look into trimethyl phosphinoxide 36.2 triethyl phosphine oxide comes at 48.3 and then if you look into phosphonium species cation it comes around 24.4 and phosphate comes around 6 and PF 5 comes around minus 80.3 and PCL 5 minus 80 and ME PF 4 comes around minus 29.9 and ME 3 PF 2 comes around minus 158. So further some more compounds are there when you have difluoromethylphosphine comes around 245 much more D shielded and then if you have methyl phosphine comes around minus 163.5 and then if you have methyl dichlorophosphine 192 and dibromomethylphosphine 184 dimethyl fluorophosphine 186 dimethyl phosphine is 99 dimethyl fluorophosphine is 96.5 dimethyl bromophosphine is 90.5 again here trimethyl phosphine sulfide is 59.1 triethyl phosphine sulfide is 54.5 and triethyl phosphonium salt comes around 40.1 and then if you have PS 3 minus it comes around 87 and PF 6 comes around 145 and this PF is very very important because in most of the metal complexes we use anion a larger anion such as hexafluorophosphate and the phosphorus chemical shift comes around 145 this comes as a something like this as a separate because of coupling with six fluorine atoms whereas 19F NMR would show a simple sig doublet something like this and PCL 4 cation shows at 86 and PCL 6 anion shows at minus 295 and it shows at 8.0. I have covered most of the compounds we come across as far as phosphorus compounds are concerned. Now let us look into very interesting examples here I have taken one example of 2 6 7 trioxa 1 4 diphosphor by cyclo 2 2 to octane something like this the structure is also shown here and if you just look into the spectrum this is phosphorus proton decoupled spectrum whereas this one is coupled spectrum shows two singlets I have labeled as alpha and beta and two signals are there both of them appear like septates having seven lines are there and where the seven lines are coming from I mean the coupled spectrum if you just look into it you see two separate septates with different spacings the moment you look at the spacings you should be able to assign without any hesitation that this is for p alpha and this is for p beta because if we consider hydrogen atoms this is one two bond coupling is there in this case 2 j p h coupling is 8.9 hertz whereas here what happens here 1 2 3 bond coupling is there here 3 bond coupling magnitude will be much smaller as a result and how the seven lines you can consider 2 2 2 6 are there and all of them are equivalent when they are equivalent they can be considered as one type of nuclei as a result again you use 2 n i plus 1 rule here 2 and number of such identical hydrogens are 6 spin half plus 1 give seven lines seven lines are seen here so sometime if we have difficulty in assigning the chemical shift because both of them in the decoupled one are showing singlets and we may have difficulty in assigning the signals whether this is p alpha or whether this is p beta or something like that in that case if we do if we record the coupled one that can help us in identifying without any ambiguity. So, this is the advantage of recording coupled one is for understanding decoupled one for simplification wherever simplification is needed we can go for decoupled spectrum wherever we want more information to have better understanding of the molecule and interpretation then we should go for coupling something like this the stronger coupling of p beta because there are only two bonds separating them again then the values are also given here you can see here 8.9 hertz and then this is 2.6 hertz. I hope now we have understood how easy it is to interpret 31 PNMR spectrum both in the decoupled as well as the coupled one. So, now let us look into 1 H NMR spectrum of the same molecule here if 1 H NMR if you look into it let me write the structure again. So, now this is alpha and this is beta we are calling and then now if you look into 1 H NMR all are identical and they couple differently to 2 phosphorus atoms alpha phosphorus and beta phosphorus and then since beta phosphorus is close to hydrogen 1 2 bond coupling first it will split into a doublet like this this is 2 j p ch and now this p alpha it is 3 bonds away and this will be 2.6. So, at the end what we get is a doublet of doublet. So, that means when we combine the information obtained from two different type of spectra we should be able to interpret and understand without any problem and sometime you can also add data obtained from IR and UV if needed and also from mass spectra metering. So, then what happens if we oxidize this compound now it is a trivalent phosphorus compound we can oxidize when we are oxidizing we can make it p double bond or p double bond yes and here when x is actually when it is oxidized it is labeled as y and x and then when x and y we can consider when x is o and y is o both of them are oxides in that case what happens it comes around minus 18.1 and 6.4 and when both are lone pairs and x y are lone pairs that is trivalent phosphorus in that case alpha comes at 90 ppm and beta comes at minus 67 ppm. So, this information directly comes from the coupled one is an MR spectrum. Then if you replace if you oxidize both the phosphorus with oxygen then p alpha comes at minus 18.1 and then beta comes at 6.4, but if we oxidize with sulfur and get corresponding disulfide then p alpha comes around 51.8 whereas p beta comes around minus 70.6. This is still lone pair is intact only p alpha is oxidized to sulfur and still p beta has lone pair intact in that case slight shift is there you can see minus 67 to this one coming it is because of secondary effect you will see because other phosphorus is now oxidized. So, it comes around 51.8 and this is because little bit alteration in the neighboring groups can also have some influence on their chemical shift can be seen from this example here. Let us look into one more example here. This is a very interesting molecule we have one ethoxy group is there on phosphorus and we have CF groups are there. First let us look into the 19 F NMR 19 F I have not discussed 19 F is also very similar to 31 p and 1 H NMR because it is also the spin is half and it is 100 percent abundant the interpretation is very similar to 1 H and very similar to 31 p NMR. So, that is the reason I am considering this molecule where we have phosphorus as well as carbon. Now, first look into 19 F NMR of this molecule here when we look into 19 F NMR of this one both of them are identical CF 3, CF 3 identical they are coupled through two bond to phosphorus. So, one phosphorus is there. So, this signal will be split into doublet and here this 2 J P F coupling is about 86.6 hertz here, but when we look into phosphorus NMR phosphorus NMR and phosphorus NMR is here 1 H decoupled 31 p NMR in this one. Since these two are identical 6 fluid atoms together split this phosphorus signal into a septate you can see here 7 lines are there and of course, one can also look into 1 H NMR. So, of course, 1 H NMR we had discussed plenty of example it is not needed. So, one can clearly see how simple to interpret data obtained from 19 F 13 C and also 31 p NMR. Let us look into few more interesting molecules. Now, let us look into another phosphorus compound here where we have direct phosphorus to hydrogen bond is there and two OMB groups are there just for convenience of interpretation I have expanded on only one of them. Now, if we look into 31 p NMR spectrum it shows a doublet with pH coupling of 715 hertz here is 1 J coupling. Usually 1 J phosphorus hydrogen couplings are very large they can go to as 1200 and 500 to 600 is very common in this case we are seeing in the coupling of 750 hertz. And then when we look into 1 H NMR in 1 H NMR what happens we have two different type of protons are there one is H directly attached to phosphorus and another one is OCH 3 and OCH 3 is 1 2 3 bond apart. So, it can show a doublet with phosphorus. So, this is the one. So, here we can see 1 2 3 bond coupling is there. So, 3 J pH is observed in this case whereas, in this one when we look into 1 H NMR the magnitude of this coupling should be same what we observed here we are observing here this is 1 J coupling this is 750 hertz. So, that way if we have again some ambiguity about the coupling constant we can verify the coupling constant value by going to NMR of other nuclei. So, now we have understood that the interpretation is very similar, but 31 P sample preparation is also very similar to 1 H sample preparation. As in other NMR experiments 31 P NMR sample must be free of particulate matter because of homogeneity problem and other things always if any particulate matter is there it is better to filter and then use clear solution. A reasonable concentration of 2 to 10 milligrams of sample dissolved in about 0.621 ml of solvent if needed the solution can be filtered through silite to remove any suspended particles. Anyway the solid will not analyze in the NMR spectrum, but they can create problem about homogeneity and that results in broadening of the signals. Unlike 1 H NMR no need to dissolve in a deteriorated solvent since common solvents do not have that 2 N P NMR nuclei to contribute to spectra. So, that is the major advantage here most of the deteriorated solvents are very expensive and also we are not using a internal standard as well. So, we are using an external standard that is 85 percent phosphoric acid that is taken in a capillary tube that capillary tube can be inserted into the NMR tube and also you can do external locking. So, we can use any solvent without any problem that saves lot of money. So, from that point of view again phosphorous NMR is much simpler and much easy, much economical and one should not try to obtain 1 H NMR spectrum from the same sample taken in common solvent that is the thing after taking phosphorous NMR. If you want to understand the proton signals we should not use the same solvent if we have not used a deteriorated solvent. So, from this point of view if you want to use the same sample for recording say 31 P 1 H 19 F and 13 C all those things then it is better to dissolve in a deteriorated solvent in which phosphorous compound is highly soluble and gives a clear solution. Since it is possible to use non-dutrated solvents 31 P NMR offers many advantages such as assaying purity readily and also one can monitor progress of reaction. For example, to understand the mechanistic aspects when we are doing reaction in the continuous reaction it comes very handy. So, this is the major advantage that is the reason variable temperature 31 P NMR is extensively used in understanding the mechanism and also to trace the nature of the intermediates this is quite helpful. So, let me stop here and take few more very interesting spectra in my next lecture and till then have an excellent time reading about NMR spectroscopy. Thank you.