Part III (DEPT and 2D-Methods)

1

   Recall that most 13 C-NMR are acquired as proton decoupled spectra because of the 13 C nucleus is significantly less abundant than the 1 H nucleus

D

istortionless

E

nhancement by

P

olarization

T

ransfer, or also called

DEPT

, is a technique that is used to compensate for some shortcomings of 13 C-NMR spectroscopy The technique utilizes the fact that different CH-functions behave differently in an experiment, where the polarization is transferred from the proton to the carbon atom

DEPT-45 # of attached hydrogens

DEPT 135 DEPT 90 DEPT 45

0 (-C-)

0 0 0

1 (CH)

up up up

2 (CH 2 )

down 0 up

3 (CH 3 )

up 0 up 2

     The original spectrum of isoamyl acetate displays only six signals due to the symmetry in the side chain 70 65 The carbonyl carbon atom at d = 172 ppm does not show up in either DEPT spectrum because it is quaternary 60 55 50 45 40 35 30 25 20 The methylene functions at d = 38 ppm and d = 61 ppm point down in the DEPT 135 15 10 5 0 1 30 1 20 1 10 1 00 9 0 8 0 7 0 spectrum 6 0 5 0 4 0 3 0 2 0 The methine function at d = 25 ppm shows up in all three DEPT spectra 1 0 0 - 1 0 - 2 0 - 3 0 - 4 0 - 5 0 - 6 0 - 7 0 The DEPT spectrum can not determine which of the signals at d and C6 d = 21 ppm and = 24 ppm belongs to C1 - 8 0 1 20 1 15 1 10 1 05 1 00 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 5 0 1 20 1 15 1 10 1 05 1 00 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 5 0 120 115 110 105 100 95 90 85 80 75

Full Spectrum 2

172.03

170 160

DEPT 135

150 1 70 1 60

DEPT 90

1 70 1 60

DEPT 45

1 50 1 50 1 70 1 60 1 50 140 1 40 1 40 1 40 130 1 30 1 30 1 30 120 1 20 1 20 1 20 110 100 1 10 1 00 1 10 1 00 1 10 1 00 90 9 0 9 0 9 0 80 70 8 0 7 0 61.63

3

6 1. 6 3 37.50

4

23.51

25.31

5 1/6

20.98

60 50 40 30 2 3. 5 1 20 2 5. 3 1 2 0. 9 8 10 5 0 3 7. 5 0 4 0 3 0 2 5. 3 1 6 0 5 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 4 0 3 0 2 3. 5 1 2 0 1 0 3 7. 5 0 2 5. 3 1 2 0. 9 8 2 0 3 1 0

    120 The full spectrum 115 110 of camphor displays 105 ten signals 100 95 The signal at d = 215 90 ppm is due to the carbonyl group 85 80 75 The signals at d = 47 ppm and d = 57 ppm are due to the other two quaternary carbon atoms 70 65 60 55 50 45 40 35 30 Thus, these three 25 carbon atoms do not 20 15 appear in any of the 10 DEPT spectra 5 0 218.40

1

200 43.55

30.06

27.19

19.21

150 100 57.49

2 3

50 4

     The range of the DEPT spectra show here is from d = 0-50 ppm (the three quaternary peaks are removed) The signal at d = 43.6 ppm (furthest to the left) is due to the methine function (C4) The signals at d = 43.4 ppm, d = 30 ppm and (C5, C6, C7) d = 27 ppm are due to methylene groups The signals at d = 19.8 ppm, d =19.2 ppm and (C8, C9, C10) d = 9 ppm are due to the methyl groups 100 50 0 -50 -100 For the methylene and the methyl groups, it is very difficult to determine which signal is due to which carbon atom without additional information 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 45 40 35 30 25 20 15 10 5 0 120 115 110 105 100 95 90 85 80 75 43.55

4 5

43.39

45 43.55

40 45 43.39

43.55

40 45 40 19.21

19.80

6 7

35 30.06

30 27.19

25 20

8 9

15 9.36

10

10

5 35 30 30.06

27.19

25 20 19.21

19.80

35 30 25 20 15 10 9.36

15 10 5 5 5

 The reaction of 1,2-diphenylpropanediol with acids leads to the formation of an aldehyde (

I

) or ketone (

II

) (or a mixture of them) depending on the conditions during the reaction (i.e., temperature, amount and type of catalyst, etc.).

 How could the 13 C-NMR spectrum and the DEPT spectra be used to determine the nature of the product?

6

 The aldehyde displays seven signals due to the symmetry of the two phenyl groups.

    Aldehyde carbon: 201 ppm Four carbon atoms: 126-145 ppm Quaternary carbon atom: 62 ppm Methyl group: 21 ppm 120 115 110 105 100 95 90 85 80 75 70 65 10 5 0 1 20 1 15 1 10 1 05 1 00 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 5 0 1 20 1 15 1 10 1 05 1 00 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 5 0 1 20 1 15 1 10 1 05 1 00 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 5 0 60 55 50 45 40 35 30 25 20 15

Full Spectrum

201.45

200

DEPT 135

2 01 . 45 2 00

DEPT 90

2 01 . 45 2 00

DEPT 45

2 01 . 45 2 00 128.30

2 signals

126.22

145.11

150 1 28 . 30 1 26 . 22 1 50 1 28 . 30 1 26 . 22 1 50 1 28 . 30 1 26 . 22 1 50 100 1 00 1 00 1 00 62.29

50 5 0 5 0 20.53

2 0. 5 3 5 0 2 0. 5 3 7 0 0

 The ketone displays eleven signals due to the lack of symmetry     Ketone carbon: 200 ppm Eight carbon atoms: 128-141 ppm Methine carbon atom: 48 ppm Methyl group: 20 ppm 50 45 40 35 30 25 20 15 10 5 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 5 0 1 20 1 15 1 10 1 05 1 00 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 5 0 1 20 1 15 1 10 1 05 1 00 9 5 9 0 8 5 8 0 7 5 7 0 6 5 6 0 5 5 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 5 0 1 20 1 15 1 10 1 05 1 00 9 5 9 0 8 5 8 0 120 115 110 105 100 95 90 85 80 75 70 65 60 55

Full Spectrum

200.20

200

DEPT 135

2 00

DEPT 90

2 00

DEPT 45

2 00 128.03

128.30

129.33

126.80

132.80

136.40

141.40

150 1 28 . 03 1 28 . 30 1 29 . 33 1 26 . 80 1 32 . 80 1 50 1 28 . 03 1 28 . 30 1 29 . 33 1 26 . 80 1 32 . 80 1 50 1 28 . 03 1 28 . 30 1 29 . 33 1 26 . 80 1 32 . 80 1 50 100 1 00 1 00 1 00 47.80

19.50

50 4 7. 8 0 5 0 1 9. 5 0 4 7. 8 0 5 0 4 7. 8 0 5 0 1 9. 5 0 8

 There is a broad variety of two-dimensional NMR techniques used in chemistry and biochemistry to deduce structures for relative complicated molecules i.e., proteins, macromolecules, etc.  Some of these experiments allow the experimenter to get additional information about his molecule since some of these techniques to look at long-range effects or connectivity between different types of atoms. 9



Method COSY NOESY ROESY HMQC HSQC HMBC Effect observed CO

rrelation

S

pectroscop

Y

, good for determining basic connectivity via (through-bond).

J

-couplings

N

uclear

O

verhauser

E

ffect

S

pectroscop

Y

, allows one to see through-space effects, useful for investigating conformation and for determining proximity of adjacent spin systems.

Not so useful for MWs in the 1 kDa range due to problems arising from the NMR correlation time.

R

otational

O

verhauser

E

ffect

S

pectroscop

Y

, same as

NOESY

, but works for all molecular weights. Has the disadvantage of producing more rf heating, hence it requires more steady state scans.

H

eteronuclear

M

ultiple

Q

uantum

C

orrelation, allows one to pair NH or CH resonances.

Often uses X-nucleus decoupling and hence gives rise to rf heating, requires reasonably well calibrated pulses and many steady state scans.

H

eteronuclear

S

ingle

Q

uantum

C

orrelation, provides the same information as but gives narrower resonances for

HMQC

, 1 H 13 C correlations. Also requires X-decoupling and hence a large number of steady state scans and is also more sensitive to pulse imperfections.

H

eteronuclear

M

ultiple

B

ond

C

orrelation, a variant of the

HMQC

pulse sequence that allows one to correlate X-nucleus shifts that are typically 2-4 bonds away from a proton.

Here we will only discuss

HMQC

spectroscopy, which permits conclusions about which carbon atom is connected to which hydrogen atom(s). The other, more advanced techniques require a more in-depth knowledge of NMR spectroscopy.

10

   1 In the HMQC spectrum, the horizontal axis displays the 13 H-NMR ( d = 0-4.5 ppm) spectrum while the vertical axis displays the C-NMR spectrum ( d = 15-65 pm) The 1 H-NMR spectrum displays the following signals: 0.7 ppm (d, 6 H, H6), 1.25 ppm (q, 2 H, H4), 1.45 ppm (m, 1 H, H5), 1.75 ppm (s, 3 H, H1) and 3.75 ppm (t, 2 H, H3) Thus, the signal at d = 21 ppm belongs clearly to the methyl group that is attached to the carbonyl group while the signal at the alkyl chain d = 22 ppm is due to the two methyl groups in

H3

1 H-NMR

H1 H5 H4 H6

11

   The signal at d = 9.25 ppm in the carbon spectrum relates to the signal at d = 0.75 ppm in the 1 H-NMR spectrum, while the two signals at d = ~19 ppm relate to the signals at d = 0.7 ppm and d = 0.82 ppm in the 1 H-NMR spectrum. The signals at d = 27, 30 and 43.3 ppm are each connected to two different hydrogen atoms (1.24 and 1.85, 1.28 and 1.61, 1.77 and 2.28 ppm) which implies that these are diastereotopic hydrogen atoms. The resulting coupling with other hydrogen atoms on neighboring carbon atoms leads to complicated splitting patterns (i.e., ddddd). Finally, the signal at d = 43.1 ppm is connected to one proton signal (2.01 ppm).

12

  

Trans-Ethyl crotonate (HMQC) dq dq q d t d

How many signals do we expect?

  1 H-NMR?

5

13 C{ 1 H}-NMR?

6

The hydrogen atom and the carbon atom in the b a -position to the carbonyl group are more shifted than the corresponding atoms in the -position because of the resonance effect

d q d t

13



Trans-Ethyl crotonate (HMBC)

 In the HMBC spectrum, the two- and three- bond couplings between protons and carbons can be seen as cross-peaks.

 J correlations sometimes break through filter; show through filter show up as multiplet cross-peaks.

14



Trans-Ethyl crotonate (HH COSY)

 The HH COSY shows the coupling network within the molecule   The triplet and quartet of the ethyl group share a cross peak The alkene protons can be seen to couple to both each another and the terminal methyl group.

15



Strychine (HMQC)

 In the HMQC spectrum, the one-bond direct CH couplings can be viewed as cross-peaks between the proton and carbon projections.

16



Strychine (HMBC)

 In the HMBC spectrum, the two- and three- bond couplings between protons and carbons can be seen as cross-peaks.

 The spectrum shows many more peaks than the HMQC 17



Strychine (HH COSY)

 The HH COSY spectrum of strychnine shows the proton coupling network within the molecule.

18