Difference between revisions of "Hannah"

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==Introduction==
 
==Introduction==
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Based on Experiment 44: NMR determination of keto-enol equilibrium constants p522
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Shoemaker, D. P., Garland, C. W., & Nibler, J. W. (1989). Experiments in physical chemistry (5. ed). McGraw Hill.
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===Tautomers of Acetylacetone (C<sub>5</sub>H<sub>8</sub>O<sub>2</sub>)===
 
===Tautomers of Acetylacetone (C<sub>5</sub>H<sub>8</sub>O<sub>2</sub>)===
  
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:* Usually the keto tautomer is favored
 
:* Usually the keto tautomer is favored
[[File:tautomerism.png|thumbnail|Figure 1:Basic reaction of keto- and enol- acetylacetone]]
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{|
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|[[File:tautomerism.png|thumbnail|Figure 1:Basic reaction of keto- and enol- acetylacetone]]
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|}
  
 
===Why Tautomerization Matters===
 
===Why Tautomerization Matters===
  
 
:* Different solvents may change the equilibrium of the keto- and enol- forms
 
:* Different solvents may change the equilibrium of the keto- and enol- forms
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::-Keto/enol equilibrium can be determined using proton NMR, as the spectra are different enough to distinguish between the tautomers
  
 
:* Tautomers in DNA replication have been hypothesized to contribute to mutagenic mispairings  
 
:* Tautomers in DNA replication have been hypothesized to contribute to mutagenic mispairings  
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:* "whereas in RNA, minor tautomeric forms have been proposed to enhance the structural and functional diversity of RNA enzymes and aptamers" (https://rnajournal.cshlp.org/content/21/1/1.full.html)
 
:* "whereas in RNA, minor tautomeric forms have been proposed to enhance the structural and functional diversity of RNA enzymes and aptamers" (https://rnajournal.cshlp.org/content/21/1/1.full.html)
  
 
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{|
[[File:F1.large.jpg|500px]]
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|[[File:F1.large.jpg|thumbnail|Figure 2: Tautomers of nucleic acid bases]]
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|}
  
 
==WebMO==
 
==WebMO==
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==Keto Acetylacetone==
 
==Keto Acetylacetone==
[[File:molecule (2).png|200px]]
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{|
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|[[File:molecule (2).png|thumbnail|Figure 3: 3D structure of keto-acetylacetone]]
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|}
  
 
Proton NMR
 
Proton NMR
[[File:nmrKetoZoomed.png|400px]]
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{|
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|[[File:nmrKetoZoomed.png|thumbnail|Figure 4: Proton NMR for keto-acetylacetone]]
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|}
  
 
Proton NMR shifts:[[:File:NMR-Chemical-Shift-PPM-Range-and-Values-Table-.png]]
 
Proton NMR shifts:[[:File:NMR-Chemical-Shift-PPM-Range-and-Values-Table-.png]]
  
 
==Enol Acetylacetone==
 
==Enol Acetylacetone==
[[File:molecule.png|200px]]
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{|
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|[[File:molecule.png|thumbnail| Figure 5: 3D structure of enol-acetylacetone]]
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|}
  
 
Proton NMR
 
Proton NMR
[[File:nmrEnol2.png|400px]]
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{|
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|[[File:nmrEnol2.png|thumbnail| Figure 6: Proton NMR of enol-acetylacetone]]
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|}
  
 
Proton NMR shifts:[[:File:NMR-Chemical-Shift-PPM-Range-and-Values-Table-.png]]
 
Proton NMR shifts:[[:File:NMR-Chemical-Shift-PPM-Range-and-Values-Table-.png]]
  
 
N.B. Hydrogen bonding deshields the proton, further increasing the chemical shift
 
N.B. Hydrogen bonding deshields the proton, further increasing the chemical shift

Latest revision as of 17:36, 5 May 2021

Introduction

Based on Experiment 44: NMR determination of keto-enol equilibrium constants p522

Shoemaker, D. P., Garland, C. W., & Nibler, J. W. (1989). Experiments in physical chemistry (5. ed). McGraw Hill.

Tautomers of Acetylacetone (C5H8O2)

  • Keto = ketone
  • Enol = alcohol
-may also be referred to as an alkenol
  • Usually the keto tautomer is favored
Figure 1:Basic reaction of keto- and enol- acetylacetone

Why Tautomerization Matters

  • Different solvents may change the equilibrium of the keto- and enol- forms
-Keto/enol equilibrium can be determined using proton NMR, as the spectra are different enough to distinguish between the tautomers
  • Tautomers in DNA replication have been hypothesized to contribute to mutagenic mispairings
Figure 2: Tautomers of nucleic acid bases

WebMO

  • All calculations were done using HF/6-31G(d) for geometry optimization
  • The products of the geometry optimizations were used to calculate the NMR spectra using the same basis sets

Keto Acetylacetone

Figure 3: 3D structure of keto-acetylacetone

Proton NMR

Figure 4: Proton NMR for keto-acetylacetone

Proton NMR shifts:File:NMR-Chemical-Shift-PPM-Range-and-Values-Table-.png

Enol Acetylacetone

Figure 5: 3D structure of enol-acetylacetone

Proton NMR

Figure 6: Proton NMR of enol-acetylacetone

Proton NMR shifts:File:NMR-Chemical-Shift-PPM-Range-and-Values-Table-.png

N.B. Hydrogen bonding deshields the proton, further increasing the chemical shift