1. ORGANIC NMR INTERPRETATION

2. ALKANES AND ALKYL HALIDES
p. 101
ALKANES AND ALKYL HALIDES
CH3—CH2—CH2—C d
CH3—F
CH3—O
CH3—Cl
CH3—Br
CH3—I
Dd ~ 2 ppm downfield
CH3—CH2-
CH3—X

3. Effect falls off with distance and is ~ 0 two C away
p. 102
Inductive effects
CH3—CH2—CH2—C d
CH3—CH2—CH2Cl d
Effect falls off with distance and is ~ 0 two C away
CH3—CH2—CH2Br d
CH3—CH2—CH2I d
Dd ½

4. CH3—CH2—CH2Cl 1.0 1.8 3.5 CH3—CH2—CH2Br 1.0 1.8 3.4 CH3—CH2—CH2I
p. 102
CH3—CH2—CH2Cl
CH3—CH2—CH2Br
CH3—CH2—CH2I
Dd ½
CH3—CH2— d

5. Inductive effects are more or less additive
p. 103
CH3—CH2—CH2X
CH3—CH2— d
Dd ½
Each extra X adds ~ 2 ppm
CH3—X CH2X CHX3 d
Ballpark ONLY!!
Inductive effects are more or less additive

6. Additional X next door has added about ½ ppm CH3—CH2—I d 1.8 3.2
I—CH2—CH2—I d
Additional X next door
has added about ½
ppm

7. In general, the more substituted, the more downfield
p. 103
In general, the more substituted, the more downfield
CH3—I CH3—CH2—I (CH3)2CH—I d
but additional alkyl groups are not as strong as –X
CH3CH2Br = (CH3)2CHBr = CH3CHBr2 = 5.5
split by 6
= 6+1
split by 1
= 1+1
I—CH(CH3)2 6H 1H

8. More complex splittings
I—CH2—CH2—CH2—CH3
t ? ? t
What about when neighbors are chemically different?
If J’s are same, then can use
splitting (# of lines) = total # of H neighbors + 1
Characteristic chain splitting in alkane chains
J=7
J=7
J=0

9. More complex splittings
I—CH2—CH2—CH2—CH3
t t

10. ANISOTROPIC EFFECTS F Spherical atoms have same effect
in all directions
p-electrons
are above and
below the plane
of molecule
so electron density is different
above or below molecule than
in plane

11. so alkenes and aromatics (and other p-bonds)
are not isotropic – they have effects that are different in
different directions – we call them ANISOTROPIC p
= Bp-electrons
= Blocal
so H feels B0 + Blocal
so appear at low field

12. LOW FIELD aromatics & alkenes appear at - is shielded - (to lower ppm)+
+ is deshielded
(to higher ppm) -
p. 105

13. methyl on an aromatic ring, double bond or carbonyl ~2.3
aromatic hydrogens ~ d 7
p. 106
X=C—CH3
methyl on an aromatic ring, double bond or carbonyl ~2.3

14. Ph—CH2—CH2—(CH2)4—CH2—CH3 7.1-7.3 2.6 1.6 1.3 1.3 0.9
Ph—CH2—CH2—(CH2)6—CH2—CH3

15. Clearing up some terminology:
Downfield
Deshielded
Low field
Greater d
Upfield
Shielded
High field
Smaller d

16. Electron Withdrawing Groups (EWG) deshield the ortho & para H’s,
o > p Benzene = 7.3
7.8
7.3
7.6
-CHO -COR -COOH -COOR -CN -NO2 -SO2
resonance effects
+ve charge deshields: less electron density at the C and H

17. 2:1:2
CHO
d 10
EWG
deshield
7.8
7.3
7.6
p. 108

18. Electron Donating groups (D:) SHIELD the ortho and para protons
o > p
6.8
7.2
7.0
Donating groups are X: (atoms with lone pairs
but not halogens)
e.g. -OH -OR -NH2 -NHR -NR2 -SR -R
resonance effect
dominates inductive
effect
negative charge
shields: more
electron density
at C and H

19. p. 109
OCH3
CH3 on O + Ar ring
~ 3.8
7.2

20. HALOGENS Not easy to predict:
Lone pairs shield by resonance but deshield because of high electronegativity

21. Part of Table on manual page 110
Increments add to d 7.27 to predict shifts, e.g.
Proton ortho to –CHO will be = 7.85

22. p. 110

23. Look carefully at peaks, they are doublets
3J ~ 8 Hz
What about to other protons?

24. p. 111 H
3JORTHO H-H = ~8Hz H
4JMETA H-H = ~2Hz
5JPARA H-H = ~0 Hz H H

25. At high fields, can use trees to get patterns, IF chemical
shifts are far apart (called 1st order spectrum if Dd >> J) H=
d (H) of d (H) H
8Hz
2Hz H=
t (HH) of d (H) H
8,8 2 H=
t (HH) of d (H) H H H=
d (H) of d (H)

26. d ~ 10 O=C-H ALDEHYDES AND coupling constant to neighbors is small
- is shielded
(to lower ppm)
+ is deshielded
(to higher ppm)
d ~ 10
AND coupling constant to neighbors is small

27. a
Karplus showed
relationship of
J and a
p. 112

28. Spectrum looks different on different instruments
60MHz
60Hz
Spectrum looks different on different instruments
J in Hertz is always independent of field
30Hz

29. ALKENE COUPLING CONSTANTS
16Hz
8Hz
2Hz

30. mono-substituted alkene R--CH=CH2
p. 114
mono-substituted alkene R--CH=CH2
Always
12 lines:
d(JL)d(JM)
d(JL)d(JS)
d(JM)d(JS)

31. p. 115
Jcis
Jtrans

32. p. 116

33. b to the substituent feels resonance effect
p. 117
Chemical shifts – much like aromatics
‘normal’ = 5.25 ppm
Geminal (same C)
always deshield
by ~ 1ppm
b to the substituent feels resonance effect

34. Manual, table page 117
Always deshield
geminal
Shield b
Deshield b

35. 4J = ~1Hz Cis Me 3J = ~7Hz Gem H Trans Ph 4J = ~1Hz
d cis to Me = – 0.07 = 4.96
d cis to Ph = – 0.28 = 5.33
See yellow pages A5
Cis Ph H
Trans Me H

36. NMR time scale is ~ 10-2 – 10-3 sec fastest NMR can measure!
ALCOHOLS, AMINES, AMIDES AND ACIDS – exchangeable H’s
Ar-CONHR and Ar-CONH2
More acidic
means more
d+ on H
NMR time scale is ~ 10-2 – 10-3 sec
fastest NMR can measure!
p. 119

37. Since acidic H exchange between molecules occurs faster
p. 119
Since acidic H exchange between molecules occurs faster
than the NMR time scale they DO NOT show coupling to any
neighbours and are typically broadened

38. To prove which is –OH peak, add D2O and shake
ROH + D2O => ROD + HOD d ~ 5.2

39. Coupling visible Shape of peak depends upon temperature
(rate of exchange is affected by temperature)
p. 120
exchange
stopped
Coupling visible
slow
exchange
fast
exchange
HO—CH3

40. p. 121
Only a
triplet
Amines: RNH2 d 1-5; ArNH2 d 5-10

41. p. 121
Amides: d 5-10
Why 2?

42. p. 121
Acids: d 10-16
d = offset (2.0) = 11.85

43. You can now start
Assignment 5