Introduction. Differences Between 1 H and 31 P NMR. - Conceptually the same as 1 H NMR -

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1 Intrductin Cnceptually the same as 1 H NMR 31 P nucleus istpic abundance 100% prevalent like 1 H Nuclear spin ½ relatively easy t interpret Excellent technique fr studying phsphrus cntaining cmpunds: rganic cmpunds crdinatin cmplexes Differences Between 1 H and 31 P NMR Chemical shifts use 85% phsphric acid as external standard Psitive chemical shifts dwnfield f standard Change in cnventin in mid1970s means ld texts and papers have shifts with ppsite sign Chemical shifts cmmnly depend n cncentratin, slvent, ther cmpunds present ~1 ppm r mre especially fr P=O grups Because standard desn t take int accunt bulk prperties f sample Samples are ften run with prtn decupling gives single sharp signal per P

2 Interpreting Spectra Chemical shift ranges fr different types f phsphrus cmpunds.

3 Example 1 cupling t H Structure and decupled 31P spectrum f P α(och 2) 3P β. Spin cupling in P(OCH 2) 3P

4 1H spectrum f P(OCH 2) 3P and prtn splitting pattern due t phsphrus. NMR spectra 31P Shifts: α=90.0, β=67.0 #sign crrected J PCH =8.9, J POCH =2.6 1H Shift: 4.45 Changing the crdinatin n P changes the chemical shifts Structure f XP(OCH 2 ) 3 PY where X and Y may be O, S, r nthing. *Table varying X and Y and crrespnding chemical shifts* Ref: Inrg Chem 1965 Example 2 cupling t F 19 F NMR is very similar t 31 P NMR (spin ½, 100% abundant istpe) Thus 19 F NMR is als a great technique fr flurinecntaining cmpunds and allws bservance f PF cupling

5 Structure, 31P spectrum (tp), and 19F spectrum (bttm) f P(CF 3 ) 2 (OCH 2 CH 3 ) 31 P shift: 92.3±0.3 #sign crrected 19 F shift: 65.3±0.20 J PCF =86.6±0.04 Ref: J. Chem. Sc Example 3 PH cupling Structure and 31P spectrum f OPH(OCH 3 ) 2. Nte the substantial splitting due t the single bnd separatin between P and H. Shift: 11 #sign crrected J PH =715

6 1H spectrum f OPH(OCH 3 ) 2. Easy t mistake dublet fr tw peaks since the splitting is s large Decupling f phsphrus peak wuld cause the dublet t cllapse int a single peak Ref: J Inrg Nucl Chem 1961 Obtaining 31 P Spectra Sample Preparatin 31 P has 100% abundance, which makes it very similar t the 1 H nucleus Unlike 13 C NMR, which requires high sample cncentratins, 31 P sample prep is very similar t 1 H sample prep Sample free f particulate matter Sln can be filtered thrugh small glass fiber if necessary (nte slid will nt be analyzed) 210 mg in mlslvent Unlike 1 H NMR, sample need nt be disslved in deuterated slvent since slvents d nt have 31 P nuclei t cntribute t signal Except when als running 1 H NMR Offers advantages (will be discussed later) Instrument Operatin Instrument prbes Fr instrument with multinuclear prbes just need t make switch in NMR sftware t 31 P experiment, this selects the frequency apprpriate fr 31 P

7 Standards Fr instrument which has separate prbes fr different nuclei must be trained by expert user External standard 85% H 3 PO 4 (external because it s s reactive) Standard in caxial tube simply insert int sample Cupling Diagram f NMR tube with inserted caxial referemce insert. Separate NMR tube prcedure #there s prbably a better way t write this (and a better way f ding it), this is just hw I used t d 31 P NMR run NMR experiment and set H 3 PO 4 signal t 0 ppm until shift stps changing stp experiment exchange reference and sample run NMR experiment f sample #discussin f 31 P standardizatin? 31 P spectra are ften run with prtns decupled Change setting as desired accrding t sftware used 31 P NMR Applicatins Assaying Sample Purity Sharp peaks can make it easy t differentiate between different phsphruscntaining species, such as starting materials Warning: a clean 31 P spectrum des nt suggest a pure cmpund, nly a mixture free f phsphruscntaining cntaminants

8 Can get ptical purity f chrial phsphrus cmpunds: add enantimer t frm adduct tw chemical shifts fr resulting diasteremers Mnitring Reactins [P 2 ] + Ni(COD) 2 [P 2 Ni] Change in 31 P intensity can be used t fllw a reactin *chemdraw f [P2] + Ni(COD)2 [P2Ni]* RBS NMR spectra f the reactin f diphsphine ligand (4.4 ppm) with nickel(0)biscyclctadiene t make a diphsphine nickel(0) cmplex (41.05 ppm) ver time. When [P 2 ] signal (4.4 ppm) stps changing relative t [P 2 Ni] (41.05 ppm) signal, reactin is cmplete Discussin As simple as taking a small aliqut frm reactin and adding it t NMR tube (filtering as needed) Huge advantage f 31 P NMR n need fr deuterated slvent Eliminates need fr checking reactin by 1 H NMR, saving time and resurces At cmpletin f reactin, crude and purified mixture can be analyzed by bth 1 H and 31 P Ref: Angew Chem Int Ed 2011 Link t RBS cnnexins chapter Say that yu want t quantify the amunt f epxide n a carbn nantube Can use catalytic reactin f methyltrixrhenium

9 A) Reactin f an epxide with methyltrixrhenium t frm a 5 membered ring. Additin f triphenylphsphine frms triphenylphsphine xide and an alkene and regenerates the Re cmplex. B) Schematic shwing the prcess f quantificatin f O n a carbn nantube. *adapted frm 2/5/13 lecture* Cnclusin 31P spectrum f experiment befre additin f Re cmplex (tp) and at the cmpletin f experiment (bttm). 31 P NMR used t quantify frmatin PhP=O frm PPh 3 Frm knwn quantity f PPh 3 can find amunt f PhP=O frmed amunt f epxide Nt nly des it allw fr quantificatin, signal frm cmpunds f interest are unaffected by presence f everything else! 31 P NMR can be used alngside 1 H NMR t characterize phsphruscntaining cmpunds

10 When used n its wn, the biggest difference frm 1 H NMR is n need fr deuterated slvent leads t different applicatins