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Can we use 2D to assign this spectrum?. 4 aromatic protons. Structure first determined by Woodward in 1948 (without NMR!). HSQC. CH 2. Identify CH, CH 2 and CH 3 peaks on HSQC (use DEPT if necessary). COSY. H-22 is a good place to start. 22. 23. HSQC.

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slide1

Can we use 2D to assign this spectrum?

4 aromatic protons

Structure first determined by Woodward in 1948 (without NMR!)

slide2

HSQC

CH2

Identify CH, CH2 and CH3 peaks on HSQC (use DEPT if necessary)

slide3

COSY

H-22 is a good place to start

22

23

slide4

HSQC

H-12 can be tentatively identified from C and H shifts

23

12 ?

Transfer this information to the HSQC spectrum

22

slide5

COSY

13

8

We can identify 11 as a CH2 and 13 as a CH from the HSQC

H-8 can distinguished from H-14 by the doublet multiplicity and shift

13-14 correlation is weak, but is seen on one side of the diagonal

13, 14

11

13

12

slide6

HSQC

14

11

13

8

23

12

Note that have a number of “dead ends” as far as COSY is concerned

22

slide7

COSY

The protons at C-15 can be identified by their correlation to H-14

14

15

15

13

slide8

COSY

Having identified the C-15 protons, we can now see the correlation to H-16

15

gem

16

15

16

slide9

HSQC

15

14

11

13

16

8

23

12

This leaves 3 CH2s, at C-17, C-18 and C-20

22

slide10

HSQC

The C-20 protons can be identified as a pair of coupled (from COSY) doublets, not coupled to anything else

slide11

COSY

The CH2s at C-17 and C-18 are left. The HSQC shows an overlapping CH2 at 1.94 ppm.

The chemical shift indicates that this must be the C-17 CH2.

The CH2 at 2.92 and 3.35 ppm must be C-18.

18

18

17

(diagonal)

slide12

HSQC

15

14

11

17

13

18

20

16

8

23

12

All protonated carbons have now been assigned

22

slide13

HMBC

We can now use HMBC to assign the non-protonated carbons (and confirm other assignments, if necessary)

C-10

H-12

H-11ax

H-11eq

slide14

HMBC

C-18

H-20

H-20

C-7

C-20

H-1

H-8

CH2-17

H-18

2 bond C-7 to H-16 correlation not observed?

H-15

slide15

COSY

TOCSY

12

8

11

13

15

14

16

15

(diagonal)

(diagonal)

17

slide16

NOESY

8

16

12

15

13

15

13

15

NOESY Avance 300

Degassed sample

Degassing removes oxygen (paramagnetic) from the sample which would otherwise provide alternate relaxation pathways.

gem

15

8

12

slide17

15N-HMBC

15N spectroscopy is very difficult!

However, we can measure 15N shifts and determine the location of the nitrogens with HMBC (AMX 500, 10 mg sample, overnight)

N-19

H-18

H-18

H-16

H-15

CH2-17

N-9

H-13

H-8

H-11