Mechanism of Air Oxidation of the Fragrance Terpene Geraniol

Mechanism of Air Oxidation of the
Fragrance Terpene
Geraniol
Bäcktorp, C. et al.
Presented by
Mr.Sarote Boonseng
J. Chem. Theory Comput.

Introduction
Geraniol is a monoterpenoid. It is the primary part of rose oil.
HO
IUPAC NAME:
3,7-Dimethyl-2,6-octadien-1-ol
Degraded by O 2 in Air
http://en.wikipedia.org/wiki/Rose
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Introduction
H 3 C
H 2
C
H 2
C
CH 2
C
H 3 C C
H 3 C
H 2
H 2
CH 2
H 2
C
CH 2
C
H 2
Cation Radical Anion
Free radical reaction in oxidation process
+O 2
Initiation: RH R
Propagation: R
ROO
ROO + R'H ROOH + R'
Termination: 2R'
non-radical products
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Introduction
Collision Theory and Activated Complex
http://www.chemguide.co.uk/physical/basicrates/collisions.gif
4
http://academics.triton.edu/faculty/lpytlewski/CHM234Chapter4PDFDiagrams/CHM234Chapter4Images/TransitionState.GIF

Introduction
Thermodynamic
ΔG
= ΔH
−TΔS
ΔG = Gibbs free energy
ΔH = enthalpy
ΔS = entropy
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Introduction
Structural prediction
Density Functional Theory (DFT)
ĤΨ = EΨ
*
< E >= Ψ Hˆ
Ψ
∫
Erwin Rudolf Josef Alexander Schrödinger
Electronic structure
Electronic properties
Spectroscopic properties
http://en.wikipedia.org/wiki/Image:Erwin_Schr%C3%B6dinger2.jpg
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Objective
To study the mechanism of oxidation of geraniol.
They focus upon the oxidation, which follows a radical
chain process.
HO
Geraniol
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Computational Method
Program: Gaussian 03
B3LYP/6-31G(d,p) and B3LYP/6-311+G(2d,p)
To estimate the structure and transition structure.
To estimate the thermodynamic contribution to the enthalpy and free energy.
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Results
The previous work
Most stable free radical
Hagvall, L.; Ba¨cktorp, C.; Svensson, S.; Nyman, G.; Bo¨rje A.; Karlberg, A.-T. Chem. Res. Toxicol. 2007, 20, 809-814.
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Results
Autoxidation pathways starting from geraniol.
1 2
3
Geraniol
A B C
D E F
G
H
I
Product
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Results
Table 1. Calculated Standard Enthalpy Changes and Standard Gibbs Free Energy
Changes in kcal mol -1 for the Reactions.
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Results
Table 2. Calculated Activation Energies, in kcal mol -1
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Results
Reaction process
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Relative energy

Conclusion
The autoxidation products of the monoterpene geraniol
have been rationalized computationally by investigated of radical
chain reaction for a model system. Both propagation steps in the
accepted mechanism, radical chain transfer and the addition of
O 2 , where found to exergonic reaction.
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Thank you
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Basis set
• Basis functions approximate orbitals of
atoms in molecule
• Linear combination of basis functions
approximates total electronic
wavefunction
• Basis functions are linear combinations
of gaussian functions
– Contracted gaussians
– Primitive gaussians
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More basis functions per atom
• Split valence basis sets
• Double-zeta: • Triple-zeta:
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Add polarization functions
• Allow orbitals to change shape
– Add p orbitals to H
– Add d orbitals to 2nd row atoms
– Add f orbitals to transition metals
• 6-31G(d) - d functions per heavy atoms
– Also denoted: 6-31G*
• 6-31G(d,p) - d functions per heavy
atoms and p functions to H atoms
– Also deonoted: 6-31G**
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Add diffuse functions
• “Large” s and p orbitals for “diffuse electrons”
– Lone pairs, anions, excited states, etc.
• 6-31+G - diffuse functions per heavy atom
• 6-31++G - diffuse functions both per heavy
atom and per H atom
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