Post on 29-Mar-2015
transcript
Example from Wang group
Work of Jiasheng Lu
Starting material
CH3
CH3
CH3B
5N+
4
1
3
2
B-
CH3
CH3
CH3B
6
7
11
8
10
9
12
UV: Postulated Reaction
6
7
11
8
10
95
N+
4
1
3
2
12B-
CH3A
CH3
CH3B
+CH3 CH3
CH3
H-NMR: Mesitylene
CH3 CH3
CH3
H-NMR: Aliphatic region
*: Starting material
*
6
7
11
8
10
95
N+
4
1
3
2
12B-
CH3A
CH3
CH3B
Me-A
Me-B
CH3 CH3
CH3
CH3 CH3
CH3
B
R R
New compound
H-NMR: Aromatic region
6
7
11
8
10
95
N+
4
1
3
2
12B-
CH3A
CH3
CH3B
*: Starting material
** * *
CH3 CH3
CH3
COSY: Full SW
Me
CH3 CH3
CH3
B
R R
Arom
atic
COSY expansion: Me vs aromatic
Me
H-C=
Me
CH3 CH3
CH3
B
R R
Starting material
Me
H-C=
CH3 CH3
CH3
B
R R
New compound Me
Me
H-C=
CH3 CH3
CH3
Methyl groups have long range coupling with ortho aromatic protons
COSY: aromatic
6
7
11
8
10
95N+
4
1
3
2
12B-
Ms
1 24
Py: 1 – 2 – 3 – 4
MsMsMs
3
Other ring : A – B – C – DNot sure which proton is H-7Start with a doublet (can be either H7 or H10) then goTo the next proton to identify the suite.
We will assign later with NOESY which one is H7
ABCD
Most deshielded
NOESY: Choosing the Mixing time
• You cannot use too short mixing time: it takes time to develop NOE. It takes T1 – too short mixing time would not show any cross peaks between protons!
• You cannot use too long mixing time. If you use too long mixing time, you can loose the labels of the chemical shifts that you record carefully during the evolution time (t1)
• For small molecules, the best mixing time is ~ 80% of the T1 value. (this is where the signal goes to null intensity in inversion recovery
Measuring relaxation time: Inversion recovery
Prepare for NOESY: evaluate relaxation time
Py: 1 – 2 – 3 – 4
Other: A – B – C – D
6
7
11
8
10
95N+
4
1
3
2
12B-
Ms
Ms
Ms
Ms
1
A 4
23
D
C
12 ?
Aromatic regionInversion recovery:
Why different rate?
Dipole Relaxation depends on the distance between protons and on the mobility of the molecule
Ms is the smallest molecule: fast motion, not efficient T1 longest relaxation time
In Pyridine ring, H4 has faster relaxation: it has one ortho neighbor (H3) and it’s close to H7 on other ring. In fact, H7 must be very close to H4 because H3 and H2 (which has 2 ortho neighbors) relax slower than H4
HA relax fast at ~ same rate as H4: same type of neighbors: may be H7 ?
H-NMR Inversion recovery: Methyl region
Ms
CH3 CH3
CH3
B
R R
Starting material
CH3 CH3
CH3
B
R R
New compound
Ms
Ms
MsMs
CH2-12
CH3 CH3
CH3
Ms is the smallest molecule: fast motion, not efficient T1 longest relaxation time
NOESY: Choosing the mixing time
• You cannot use too short mixing time: it takes time to develop NOE. It takes T1 – too short mixing time would not show any cross peaks between protons!
• You cannot use too long mixing time. If you use too long mixing time, you can loose the labels of the chemical shifts that you record carefully during the evolution time (t1)
• For small molecules, the best mixing time is ~ 80% of the T1 value. (this is where the signal goes to null intensity in inversion recovery
In our case, MIXING = 2 sec. will do good job according to T1
NOESY : mix time 2sMethyl vs aromatic
Me
Ms
CH3 CH3
CH3
B
R R
Starting material
MsPy
Py: 1 – 2 – 3 – 4
Other: A – B – C – D
6
7
11
8
10
95N+
4
1
3
2
12B-
Ms
Ms12 ?A D C B1 4 23
CH3 CH3
CH3
Me
Me
New compound
Me
Me
NOESY :mix time 2sAromatic
Py: 1 – 2 – 3 – 4
Other: A – B – C – D
6
7
11
8
10
95N+
4
1
3
2
12B-
Ms
MsMs1 A 4
Ms
D C12
23B
A
7 – 8 – 9 – 10
C
12
D
D
What’s left? Assign C13
Use HSQC to assign carbons that are directly attached to protons 1JCH
Use HMBC to assign carbons that are further away from protons nJCH
(HSQC : Heteronuclear Single Quantum Correlation)
(HMBC: Heteronuclear Multiple Bond Correlation)
HSQC: aromatic Ms
Ms1 7 4
Ms
10 912
238
6
7
11
8
10
95N+
4
1
3
2
12B-
Ms
C1: 136.2
C2: 115.5
C3: 127.9
C4: 121.5
C7: 124.5
C8: 119.5
Ms: 127.4
C9: 128.6
C10: 128.4
C12: 118.5
HSQC: MethylMs
MsMs
CH3 CH3
CH3
B
R R
Starting material
CH3 CH3
CH3
B
R R
New compound
CH3 CH3
CH3
MsCH221.0
25.2
20.6
Ms
22.5
21.1
HMBC: MethylMs
MsMs
CH3 CH3
CH3
B
R R
Starting material
CH3 CH3
CH3
B
R R
New compound
CH3 CH3
CH3
MsCH221.0
25.2
20.6
Ms
22.5
21.1136.7
127.5
140.2
138.9
HMBC: aromatic Ms
Ms1 7 4
Ms
10 912
238
6
7
11
8
10
95N+
4
1
3
2
12B-
Ms
C1: 136.2
C2: 115.5
C3: 127.9
C4: 121.5
C7: 124.5
C8: 119.5
C9: 128.6
C10: 128.4
C12: 118.5
CH3 CH3
CH3
B
R R
22.5
21.1136.7
127.5
140.2
138.9
2
C5: 142.3
6C6: 118.8
11
9
C11: 145.6
10
11