3.15 NMR spectroscopy Different types of NMR There are two main types of NMR 1. C 13 NMR 2. H (proton) NMR

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1 .5 NMR spetrosopy Different types of NMR There re two min types of NMR. NMR. (proton) NMR There is only round % in orgni moleules ut modern NMR mhines re sensitive enough to give full spetr for The spetr is simpler spetrum thn the NMR Equivlent ron toms. In NMR spetrum, there is one signl (pek) for eh set of equivlent toms. d d 4 peks peks 4 peks, dinitroenzene, dinitroenzene,4 dinitroenzene N l peks peks N 4 peks peks d peks d e N 5 peks Equivlent ydrogen toms. In n NMR spetrum, there is one signl for eh set of equivlent toms. In ddition the intensity (integrtion vlue) of eh signl is proportionl to the numer of equivlent toms it represents. Ethnol hs groups of different hydrogen toms d d d 4sets of equivlent s: rtio 6::: signl sets of equivlent s: rtio ::9 sets of equivlent s: rtio :: sets of equivlent s: rtio :: Br d 4 sets of equivlent s: rtio ::: N Goly hemrevise.org

2 Solvents Smples re dissolved in solvents without ny toms, e.g. l 4, Dl. This mens tht in the NMR the solvent will not give ny peks The sme solvent is used in NMR nd in this se there will e one pek due to the solvent tht will pper on the spetrum. owever, it is known where this pek is so it n e ignored. In the exm it is likely this pek will not our on the spetr. lirtion nd shift A smll mount of TMS (tetrmethylsilne) is dded to the smple to lirte the spetrum TMS is used euse: its signl is wy from ll the others it only gives one signl it is non-toxi it is inert it hs low oiling point nd so n e removed from smple esily Si tetrmethylsilne The sme lirtion ompound is used for oth nd NMR The spetr re reorded on sle known s the hemil shift (δ), whih is how muh the field hs shifted wy from the field for TMS.. The δ is mesure in prts per million (ppm) is reltive sle of how fr the frequeny of the proton signl hs shifted wy from tht for TMS δ hemil shift (ppm) 0 NMR shift The δ depends on wht other toms/groups re ner the more eletronegtive groups gives greter shift. δ ppm N Goly hemrevise.org δ ppm

3 NMR shift ppm N Goly hemrevise.org

4 Spin-Spin oupling in Nmr In high resolution NMR eh signl in the spetrum n e split into further lines due to inequivlent s on neighouring toms. Nulei in identil hemil environments do not show oupling mongst themselves! Splitting of pek = numer of inequivlent s on neighouring toms + signl singlet doulet triplet qurtet pperne Split numer of peks numer of neighouring inequivlent toms 4 0 reltive size : :: ::: The pek due to group will e triplet s it is next to ( ron with s) The pek due to group will e qurtet s it is next to ( ron with s) The pek due to group will e singlet s it is next to ron with no s) The pek due to group will e triplet s it is next to ron with s Shift Integrtion tre The pek due to group will e singlet s it is next to ron with 0 s Shift.-.6 Integrtion tre The pek due to group will e qurtet s it is next to ron with s Shift.7-4. Integrtion tre ppm ydrogens onded to Nitrogen or xygen usully do not ouple with other protons nd pper s singlets on the NMR spetr The pek due to group will e triplet s it is next to ron with s Shift Integrtion tre The pek due to group will e qurtet s it is next to ron with s Shift.7-4. Integrtion tre Ethnol The pek due to group will e singlet s the ydrogen is onded to n oxygen nd this does not split Shift Integrtion tre N Goly hemrevise.org 4

5 Bringing it ll together. Work out empiril formul Elementl nlysis 66.6%.8%.9%. Using moleulr ion pek m/z vlue from mss spetrum lulte Moleulr formul moleulr ion pek m/z vlue= /.8/.9/6 =5.555 =.8 = =4 =8 = Mr empiril formul 4 8 = 7 If Mr moleulr formul 44 then ompound is 8 6. Use IR spetr to identify min onds/funtionl group 8 6 ould e n ester, roxyli id or omintion of lohol nd ronyl. Look for IR spetr for = nd - onds There is = ut no - sorptions, so must e n ester. - = 4. Use NMR spetr to give detils of ron hin 4 peks only 4 different environments. singlet of re 9 At δ =0.9 Mens groups 9 Pek t δ 4 shows Are suggests Qurtet mens next to Pek t δ. shows = Are suggests Singlet mens djent to with no hydrogens Pek t δ. shows R- Are mens Triplet mens next to 5 4 δ ppm Put ll together to give finl struture N Goly hemrevise.org 5