Inorganic Spectroscopy NMR

��ات ا��آ� ر أ�� ا��ن

1

2Dr. USAMA El-AYAAN

Nuclear Magnetic

Resonance Spectroscopy

� ا�� وي ا�� ا�� وي ا��ا��ا��

Introduction

• NMR is the single most widely used physical technique because its wide application.

• It is used to study a wide variety of nuclei:• It is used to study a wide variety of nuclei:– 1H– 13C– 15N– 19F– 31P

4

��ى �� - �� أ��اد ��ل آ�� ا��رات��spinً% ��و$ً� و�� ! ن �

quantum numbers �&'��. Iو$'&� ��د ا�)�ل �- �� ل ا��* ا��رات�� +)�'ًا ��وى�ً�,�-�.(& �&1 أ&0� ذ� . ��&ً

* ا��رو1�2 ا��).�-�,*$56* ه�ا ا��م 1Hا��رو1�2 ��ً �5+ 7��8 5�ت :9�6 +*,�-�.(& '�(+“tiny magnet ” .

Dr. USAMA El-AYAAN

The NMR Spectrometer

5=>

Dr. USAMA El-AYAAN

Nuclear Spin•�� ن �(� �� ا�)�دى ا�'�&%ذات ا��د ا�#رى أو ا��د ا '�.

�� /�ل �� -� ه#+ •�� .آ�� 1��2'0 ا

• A nucleus with an odd atomic number or an odd mass number has a nuclear spin.

• The spinning charged nucleus generates a magnetic field.

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=>Dr. USAMA El-AYAAN

External Magnetic Field �� ه#ة)4 �6(-�� 4ض ��9�(� ;�ر:% ��%/�ل �9ى ا

�4?�ف آ��= >�� When placed in an external field, spinning protons act like bar magnets.

7Dr. USAMA El-AYAAN

Two Energy States

�� NMRA4�4:(�ز دا;0�ا

ا��/�ل �� أو 6 ا��B ��Cآ�(�DEF1��2'0 آ�� ا��.

Dr. USAMA El-AYAAN 8

DEF1��2'0 آ�� ا��.

��- G��4 �EE∆ا��H�Fا��

0J��4 )ا��اد� /�ل %9(��ت ا�% αααα ا�� ا��Eو4

ββββ ا��

8Dr. USAMA El-AYAAN

∆E and Magnet Strength

• Energy difference is proportional to the

magnetic field strength.

• ∆∆∆∆E = hνννν = γγγγ h B0

2ππππStrength of the applied mag. filed

• Gyromagnetic ratio, γγγγ, is a constant for each

nucleus (26,753 s-1gauss-1 for H).

• In a 14,092 gauss field, a 60 MHz photon is

required to flip a proton.

• Low energy, radio frequency.

9Dr. USAMA El-AYAAN

Magnetic Shielding

• If all protons absorbed the same amount of

energy in a given magnetic field, not much

information could be obtained.

• But protons are surrounded by electrons • But protons are surrounded by electrons

that shield them from the external field.

• Circulating electrons create an induced

magnetic field that opposes the external

magnetic field.

10Dr. USAMA El-AYAAN

Magnetic Shielding

�)= ا��/�ل ا��K9 DEF اذا• ��- �H�Fا� =(��ت ا�?L آ0 ا��Eو4�ت ��H � ��M'6 ا�H �4NMR.

��ت �� N2'��و��ت • � ا��/�ل ا��%ا��Eو4- �)E/�4%:ر�Oا� . ��ت �� N2'��و��ت • � ا��/�ل ا��%ا��Eو4- �)E/�4%:ر�Oا� .

ل ا�� اة ��P1 -�� /�ل •B ت�� %دوران ا�Q'��و.ا��Oر:%-'= ا��/�ل

Dr. USAMA El-AYAAN 11

Shielded Protons

�SBK ز��دة �Rة ا��/�ل )�� ) -&% ا��-��H %9 ب ��B ا��Eو4 ن ا�� /� آ ن وه#ة اQ�?�ص��ث �'%) -&% ا��ر(- W� ا�C��دة ��ور�� &��

�ً2 .ا��Eو4 ن �/Magnetic field strength must be increased for a shielded proton to flip at the same frequency.


Protons in a Molecule

Depending on their chemical

environment, protons in a molecule

are shielded by different amounts.are shielded by different amounts.

13=>Dr. USAMA El-AYAAN

• The number of signals shows how many different kinds of protons are present.

• The location of the signals shows how shielded or deshieldedthe proton is.

��(4 ��- �&YNMRNMRه��ك دا��Z أر62 أY&� -�� 4)��ه��ك دا��Z أر62 أNMR signalNMR signal

shielded or deshieldedthe proton is.

• The intensity of the signal shows the number of protons of that type.

• Signal splitting shows the number of protons on adjacent atoms. =>


��(4 ��- �&YNMRNMRه��ك دا��Z أر62 أY&� -�� 4)��ه��ك دا��Z أر62 أ

� signals ��د -1•�� ا ��و��ت ا� ا��اع ا

�%$# �signal"�ن -2• ��&' وا ,*$#و�%�د+ *�ل ا ��و��ن )�

و�� إ � ��د ا ��و��ت �� 0 ا '�ع signal/�ة -3•

•4- signal splitting ورة�$� و�� إ � ��د ا ��و��ت �� ا 3رة ا


ShieldingDeshielding A/B %&-0أHأ �ًE/B


• TMS is added to the sample.

• Since silicon is less electronegative

than carbon, TMS protons are highly

Si

CH3

CH3

CH3

H3C Si

CH3

CH3

CH3

H3C

than carbon, TMS protons are highly

shielded. Signal defined as zero.

• Organic protons absorb downfield (to

the left) of the TMS signal.


Chemical Shift

• Measured in parts per million.

• Ratio of shift downfield from TMS (Hz) to

total spectrometer frequency (Hz).

• Same value for 60, 100, or 300 MHz • Same value for 60, 100, or 300 MHz

machine.

• Called the delta scale.


�ت TMS إ<�=�ام�� آ��CD F* ��'!� &�ا:�CD Eط -�A ا�@'و �5�F !*ا��=�G�ا� EH�& �.5*ا��C1 ا�H NMR .

Si CH3CH3

CH3

CH

tetramethylsilane

“TMS”

reference compound :را�I�> F�0& Eن �ً@KL *�M7 ا �� 'و

9��. !* ا�)

TMS

shift in Hz

0

CH3

n

Highly shielded

protons appear

way upfield.

Chemists originally

thought no other

compound would

come at a higher

field than TMS.

downfield


11 . .�ً�Z0 آ��; Aآ�ن K� 0�M 62ً�را�Z0 آ��; Aآ�ن K� 0�M 62را . .22 . . �^(O� در:� _&��ن `� ��F� 0Z� �^(O� در:� _&��ن `� ��F� 0Z�2626..5 5 ooCC � م اC� إذا `� G&O(0 ا��، �#ا �م ا C� إذا `� G&O(0 ا��ا #� ، . . ة /�ل ��% وا�Bة . . 33H ��- �)��: G��4 `4�� ة /�ل ��% وا�Bة �2و4H ��- �)��: G��4 `4�� أ-&% � /�ل أ-&% � /�ل ) ) �#ا ��)f آ(�� eO% وا��B#ا ��)f آ(�� eO% وا�B((�2و4

�6 ا��&�0 ��&� ��(�Fط ا� FO6 ا��&�0ا�� &� ��(�Fط ا� FOل . . ا� %FOا� h�Fا� #;P�ل و %FOا� h�Fا� #;P�وTMS TMS س��J %&- �(< ��ا��د ��Jس ا��J %&- �(< ��ا��د ��Jا�δδδδδδδδد�� وا��% ��C/2 �)�- �Eء � ا��&� ن د�� وا��% ��C/2 �)�- �Eء � ا��&� ن (ppm) (ppm) ..

%F; 6:ن آ��K0 ا��M 62دة را�م �O��4 ذا�� %F; 6:ن آ��K0 ا��M 62دة را�م �O��4 ذا�� h�� ط F; 6Hا �9�� h�� ط F; 6Hا �9�� (&�Oت ا�� ت ا��O&)� ا��Eو4 :: C:NMR NMR��Yت ا�� اد ا��^ �� -�� C: h�� 0�&�4��Yت ا�� اد ا��^ �� -�� h�� 0�&�4 9%9%ا��Eو4

C4�)��2 �)�- ًا�E� ��HHz ��4 اQزا�E� �Bو4 ن �� ة �4دد ا�/(�ز ا��Oم 9% ا��JسH %&- . 9'&�� آ�ن ا�/(�ز

��E��&� C4�)ام ا��O�ا��1'&� -�� إ��ت � ا �C��ح �&�Eو4- :←←←←

TMS

shift in Hz

0n

downfield

ة �4دد ا�/(�ز ا��Oم 9% ا��JسH %&- . 9'&�� آ�ن ا�/(�ز. ذو �4دد -��% ��?0 -&% إزا�B أ-&%

Higher frequencies= larger shifts in Hz.

��ت � ا �C��ح �&�Eو4- :←←←←

20 Dr. USAMA El-AYAAN

parts perparts perparts perparts per

millionmillionmillionmillion

��Z��'ا� �BزاQا ))δδδδδδδδ ( (““ف��Fة ا�� H ��2 ��4n `�2�o ��Hف��Fة ا�� H ��2 ��4n `�2�o ��H””

The shifts from TMS in Hz are bigger in higher fiel d: instruments (500 MHz > 400 MHz > 300 MHz > 200 MHz )

We can adjust the shift to a field-independent valu e,the “chemical shift” in the following way:

chemical

shift= δδδδ =

shift in Hz

spectrometer frequency in MHz= ppm

This division gives a number independent

of the instrument used.

��H =(� ��- �)f� م &� Aآ�9% � ة ا��Fف ا��Oم �2δδδδو4 ن ��H ��4 621 Dr. USAMA El-AYAAN

Delta Scale

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=>Dr. USAMA El-AYAAN

Location of Signals

• More electronegative

atoms deshield more and

give larger shift values.

• Effect decreases with • Effect decreases with

distance.

• Additional

electronegative atoms

cause increase in chemical

shift.


��

ل ا�� اة ��AE � ��ف A/�2 ا�� اة � ا��oP ��2/�ل �B ��ز��دة ا�'�9�M ا�Q'��و�` أن �/�h�� 0 ا�� اة �shielding ( ��- �)f(ا��% ا��Oر:% PR �وه#ا . /�ل ��% -��%

ل ا�� اة ��AE � ��ف A/BK��2 ا�� اة � ا��oP ��2/�ل �B ��GJ ا�'�9�M ا�Q'��و�� /�h�� 0 ا�� اة �f(� -�� /�ل )deshielding(ا��% ا��Oر:%

W(O� %��. �downfield (deshielding) = left side of spectrum

upfield (shielding) = right side of spectrum

ا�� ا0 ا��oqة -&% اCB 6Hم اQ�?�صا�� ا0 ا��oqة -&% اCB 6Hم اQ�?�ص

�upfield (shielding) = right side of spectrum�delta values increase from right to left!

CHCl3 CH2Cl2 CH3Cl

7.27 5.30 3.05 ppm

mostdeshielded

� :r�Mل�Aة ا�� H ��oP4

24 Dr. USAMA El-AYAAN

Typical Values


12121212C is not NMRC is not NMRC is not NMRC is not NMR----activeactiveactiveactive I = I = I = I = 0000

however….however….however….however…. 13131313C does have spin, I = C does have spin, I = C does have spin, I = C does have spin, I = 1111////2 2 2 2 (odd mass)(odd mass)(odd mass)(odd mass)

4 ا:� ا�(��رو:�� (%1.08)9% ا��EF 13- إ�O)�ض ��E و: د ا�'�2 ن1.1.1.1. �E��2 ��% )100�Jر

��(�Fرات ا��RQ1313اC NMRC NMR ��(�Fرات ا��RQا � h1أ��H NMR AE�2 :

1313C NMR C NMR h��h��

4 ا:� ا�(��رو:�� (%1.08)9% ا��EF 13- إ�O)�ض ��E و: د ا�'�2 ن1.1.1.1. �E��2 ��% )100�Jر�ًE��J4.(

v�B أن “ . 0�&H�Jر�� C��2م ا��% �� اة ا�(��رو:�� 13- ا��Cم ا��% �� اة ا�'�2 ن2.2.2.2. L2�Mا�Gyromagnetic constantGyromagnetic constantGyromagnetic constantGyromagnetic constant:γγγγن اة ا�'�2�� E��2 -13 اة � ��B %9 `��H 62ر

�. ”ا�(��رو:�

h�� 0�/�4 �1313#اC NMR C NMR h�F2 ��ا�#ى 1H NMR�P;# و�Hً� أ� ل ��M'2�Jر).د)1-2 �J�H��w �4/�&� 9% ز� H&�0 :�ًا

%9 ��Z��'ا� �BزاQى ا�1313C NMRC NMR ��B %9 `� �E1أآH NMR

0 - 220 ppm26Dr. USAMA El-AYAAN

“ Typical” 13C NMR

the wave function for the highest occupied molecular orbital for Carbon 60

1313C NMR C NMR h��h��

27

Dr. Richard Smalley

Dr. USAMA El-AYAAN

IFeq

Feq Feq

Feq

Fax IF5 has a square-pyramidal geometry, with one axial fluorine and four equitorial fluorines. Coupling between the inequivalent fluorinesshould give rise to a quintet for the F axresonance and a doublet for the F eqresonance

Feq Feq

28

eqresonance

Fax quintet

Feq doublet

Brisdon, p. 34Dr. USAMA El-AYAAN

31P NMR Spectroscopy

Compound δ (ppm) Compound δ (ppm)

As with As with 1919F NMR spectroscopy, F NMR spectroscopy, 3131P NMR spectroscopy is a fairly routine P NMR spectroscopy is a fairly routine experiment for experiment for phosphinesphosphines, , phosphitesphosphites, , phosphinephosphine oxides,oxides, phosphates, phosphates, and other phosphorus containing compounds, as it is and other phosphorus containing compounds, as it is 100100% abundant. % abundant. The chemical shift is sensitive to the oxidation st ate (P(III) The chemical shift is sensitive to the oxidation st ate (P(III) vsvs P(V))P(V)) and and the nature of the groups attached to the P atom. the nature of the groups attached to the P atom.

PMe3 -62 Me3PO +36

PEt3 -20 Et3PO +48

PBu3 -33 Bu3PO +43

PPh3 -7 Ph3PO +29

[PEt4]+ +40 P(OMe)3 +140

[PF6]- -145 P(OEt)3 +13829Dr. USAMA El-AYAAN

31P NMR for metal phosphine complexes

Cl

M

PR3

ClR3P

R3P ClCl

M

ClPR3R3P

R3P Cl

30

fac-[M(PR3)3Cl3] mer-[M(PR3)3Cl3]

All three PR3 ligands are in the same chemical environment, so the 31P NMR spectrum would have only one resonance

There are two PR3 ligands are in the same chemical environment (trans to each other) and the other in a different environment, so the 31P NMR spectrum would have two resonances, with a 2:1 relative integration

Dr. USAMA El-AYAAN

31P NMR for metal phosphine complexes

Cl

M

PR3

ClR3P

R3P ClCl

M

ClPR3R3P

R3P Cl

fac-[M(PR ) Cl ] mer-[M(PR ) Cl ]

31

fac-[M(PR3)3Cl3] mer-[M(PR3)3Cl3]

All three PR3 ligands are in the same chemical environment, so the 31P NMR spectrum would have only one resonance

There are two PR3 ligands are in the same chemical environment (trans to each other) and the other in a different environment, so the 31P NMR spectrum would have two resonances, with a 2:1 relative integration

Dr. USAMA El-AYAAN

19F and 31P NMR spectra of the PF 6- ion

FF F

-

In the octahedral PF6- ion, all six fluorine

nuclei are identical.

The 19F NMR spectrum would be expected to show coupling of the six equivalent F

P

FF F

F F

32

to show coupling of the six equivalent F nuclei to one P nucleus to give a doubletfor the F resonance

The 31P NMR spectrum would be expected to show coupling of the P nucleus to 6 F nuclei, giving a regular “septet” for the P resonance.

Dr. USAMA El-AYAAN

Coupling

• Consider one H split by one F

33

Brisdon, p. 36

Dr. USAMA El-AYAAN

Coupling

• I = 1/2

34

Brisdon, p. 37

Dr. USAMA El-AYAAN

Coupling• I = 1/2

35

Brisdon, p. 38

Dr. USAMA El-AYAAN

Si(OCH2CH3)2JJ = (= (44..377377-- 44..342342))ppmppm x x 200 200 MHz = MHz = 7 7 Hz


19F and 31P NMR spectra of the PF6- ion

1JPF = 709 Hz (typical range is 500-1500 Hz

doublet septet

37

Brisdon, p. 38

Dr. USAMA El-AYAAN

31P NMR spectrum

A doublet of triplets

1JPF(axial)

38

19F NMR spectrum

1JPF(equitorial)

Iggo, NMR Spectroscopy in Inorganic Chemistry, p. 38-40Dr. USAMA El-AYAAN

31P NMR spectrum of [Rh(PPh 3)3Cl]

Wilkinson’sWilkinson’s CatalystCatalyst ((RhRh(PPh(PPh33))33Cl)Cl) hashas threethree PPhPPh33 ligandsligands inintwotwo differentdifferent chemicalchemical environmentsenvironments (( ciscis andand transtrans toto thethe ClCl --

ligandligand)).. InIn additionaddition toto thethe twotwo setssets ofof PP nucleinuclei couplingcoupling totoeacheach other,other, theythey areare alsoalso coupledcoupled toto 103103RhRh (I(I == ½)½)..

39

Iggo, NMR Spectroscopy in Inorganic Chemistry, p. 36Dr. USAMA El-AYAAN


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Inorganic Spectroscopy NMR