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H-NMR Correlation for the Transformation of Compound 25 to Compound 26

Hydra

 

Compound 25

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Assignment

Shift (300 MHz)

Integration

Splitting Pattern

J-Values

Assignment

Shift (300 MHz)

Integration

Splitting Pattern

J-Values

A:

2.62 ppm

2H

Broad Singlet

 

I:

7.71-7.67 ppm

1H

Multiplet

 

B:

5.49-5.46 ppm

2H

Multiplet

 

J:

2.12-1.89 ppm

2H

Multiplet

 

C:

5.92-5.89 ppm

2H

Multiplet

 

K:

2.12-1.89 ppm

2H

Multiplet

 

D:

4.27 ppm

2H

Singlet

 

L:

4.8-4.78 ppm

1H

Multiplet

 

E:

6.82 ppm

1H

Doublet

J = 15.2 Hz

M:

5.49 ppm

1H

Multiplet

 

F:

7.29 ppm

1H

Doublet

J = 15.2 Hz

N:

0.11 ppm

6H

Singlet

 

G:

7.92 ppm

2H

Doublet

J = 7.6 Hz

O:

0.91 ppm

9H

Singlet

 

H:

7.61-7.57 ppm

2H

Multiplet

 

 

 

 

 

 

 

Rationale

A:

Carbon A is methylene bridge attached to two sp2 atoms. The electronegativity difference between the sp3 carbon and the two sp2 carbons deshields the hydrogens in Group A. Because Group A is attached to 2 sp2 atoms instead of one, its hydrogens are more downfield than Groups J & K’s hydrogens.

         B:

Nonaromatic, cyclic carbon double bonds exhibit chemical shifts of roughly 5 ppm to 6 ppm. Because Group C should appear more downfield than B, the 5.49 - 5.46 ppm peak has to be Group B.

C:

Carbon C is more downfield than Carbon B because it’s bound to a tertiary carbon, rather than a secondary carbon. Thus, Group C is the 5.92 – 5.89 peak.

D:

When a carbon is directly attached to an oxygen atom, the hydrogens attached to it experience a shift of about 4 ppm.

E:

Because Carbon E is a sp2 hybridized carbon, its ppm value is expected to be at least above 5 ppm. The ester substituent and resonance contribution raises it ppm value well above Group B & C’s hydrogens. 

F:

Simarly to Group E, resonance contribution helps raise the raise ppm value of Group F to be higher than Group B & C. Because Group F is attached to a more electronegative atom than Group E, it is more downfield.

G:

Groups G, H, and I are part of an phenyl group, so their ppm values are expected to be from 7 - 8 ppm. Group G is more downfield than Group H because of resonance contribution that places a positive charges on Carbons G & I. Group G is more downfield than Group I because it’s closer to the electronegative sulfur; and therefore, receives more inductive effect.

H:

Group H is more upfield than Groups G & I because there are no significant resonances that place a positive charge on the H-Carbons.

I:

Group I is more downfield than Groups H because of a resonance contributor that place a positive charge on Carbon I.

J:

Carbon J is a methylene bridge attached to one sp2 atom. Because it is only attached to one sp2 atom, it is not as deshieled as Carbon A.

K:

Very hard to chemically distinguish between Group J; therefore the shift is same.

L:

Carbons L & M are both sp2 carbons, so their ppm values should be roughly 5 - 6 ppm. By looking at the integration value, it becomes apparent that Group L & M correlate to the 4.8 & 5.49 ppm peaks, and NOT the 5.49 & 5.92 peaks. The integration values are the determining factor between distinguishing Groups B & C from Groups L & M. Group M is more downfield than L; thus, Group L correlates to the 4.8 – 4.78 ppm peaks.

M:

Group M is more downfield than Group L because the oxygen atom is a substituent of Carbon M’s double bond, and not Carbon L’s. Therefore, Group M is expected to receive more inductive effect.

N:

The 0.11 ppm peak corresponds to the two methyls directly attached to the silicon atom. Silicon is less electronegative than carbon which causes the carbon to become shielded.

O:

The 0.91 ppm peak corresponds to the three methyl groups attached to the carbon attached to the silicon. Methyls usually show up around 1 ppm, but these methyls are being slightly shielded by the silicon

Compound 25 <---> Coumpound 26 <---> Top <---> Home

Compound 26

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Assignment

Shift

Integration

Splitting Pattern

J-Values

A

2.78-2,76 ppm

2H

 

 

B

5.68-5.60 ppm

2H

Multiplet

 

C

6.12-6.07 ppm

2H

Multiplet

 

D

4.30-4.15 ppm

2H

Doublet

J = 10 Hz

E

7.55 ppm

1H

Doublet

J = 6.8 Hz

F

2.08-1.99 ppm

2H

Multiplet

 

G

2.08-1.99 ppm

2H

 

 

H

2.08-1.99 ppm

2H

 

 

I

3.49-3.47 ppm

1H

Multiplet

 

 

Rationale

A:

Carbon A is methylene bridge attached to two sp2 atoms. The electronegativity difference between the sp3 carbon and the two sp2 carbons deshields the hydrogens.

     B:

The 5.68 ~ 5.60 ppm peak correlates to Group B because nonaromatic, cyclic Carbon double bonds exhibit chemical shifts of about 5 ppm to 6 ppm. Group C is more downfield than B.

C:

Carbon C is more downfield than Carbon B because it’s bound to a tertiary carbon, rather than a secondary carbon. Thus, Group C is the 6.12 – 6.07 peak.

D:

When a carbon is directly attached to an oxygen atom, the hydrogens attached to it experience a shift of about 4 ppm.

E:

The most downfield peak (7.55 ppm) corresponds to Group E. Ordinarily, nonaromatic, sp2 carbons have hydrogen shifts of 5 ~ 6 ppm. However, Carbon E is further downfield due to the resonance contribution and inductive effect of the ester. The inductive effect of the ketone also deshields it.

F:

Like Carbon I, Carbon F is alpha to the ketone, so its ppm value should be a little more than 2 ppm.  Group F is more upfield than Group I because it is not attached to an sp2 hybridized atom.

G:

Carbons G & H are methylene bridges attached to a tertiary atom and another methylene bridge. Compared to the other atoms in the molecule, they should have the lowest ppm shift. The transformation of molecule 25 to 26 has caused the Carbons J & K in molecule 25 (now H & G) to become more slightly more shielded.

H:

Very hard to chemically distinguish between Group G; therefore the shift is same.

I:

Carbon I is tertiary and attached to an sp2 carbon. The electronegativity difference between the sp3 carbon and the sp2 carbon deshields the hydrogens in Group I. Additionally, inductive effects of the carbonyl deshields it further.

Compound 25 <---> Coumpound 26 <---> Top <---> Home

 

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