Silber spiegel - SwissEduc

42
3/04
Mechanisms
Mechanism 1:
ΔV Δ (I (I1
) = V (I ) - V (R)
1
ΔV Δ (TS (TS1
) = V (TS ) - V (R)
1
ΔV Δ A V A V = V (TS (TS1
) - V (I1 )
ΔV Δ (I (I2
) = V (I ) - V (R)
2
ΔV° Δ = V (P) - V (R)
Mechanism 2:
ΔV Δ (TS (TS1
) = V (TS ) - V (R) = ΔV
1 ΔV A ΔV A
ΔV Δ (I (I1
) = V (I ) - V (R)
1
ΔV Δ (TS (TS2
) = V (TS ) - V (R)
2
ΔV Δ A VA V = V (TS ) - V (I )
2 2 1
ΔV Δ (I (I2
) = V (I ) - V (R)
2
ΔV Δ (TS (TS3
) = V (TS ) - V (R)
3
ΔV Δ A VA V = V (TS ) - V (I )
3 3 2
ΔV Δ (I (I3
) = V (I ) - V (R)
3
ΔV Δ (TS (TS4
) = V (TS ) - V (R)
4
ΔV Δ A VA V = V (TS ) - V (I )
4 4 3
ΔV Δ (I (I4
) = V (I ) - V (R)
4
ΔV° Δ = V (P) - V (R)
Mechanism 3:
ΔV Δ (I (I1
) = V (I ) - V (R)
1
ΔV Δ (TS (TS1
) = V (TS ) - V (R)
1
ΔV Δ A V A V = V (TS (TS1
) - V (I1 )
ΔV Δ (I (I2
) = V (I ) - V (R)
2
ΔV° Δ = V (P) - V (R)
V 1
2. Theoretical Background
An introduction to quantum chemistry is
probably best reserved for students having a
background equivalent to at least two or three
semesters of physical chemistry. With help from
the instructor, it should be straightforward to
persuade the students that quantum chemistry
methods can offer important support for
proposing mechanisms. Examples for carrying
out quantum chemical calculations like those
presented here can be found in reference [4].
3. Computational Details
All calculations were carried out at the Restricted Hartree–Fock (RHF) level
and the standard double–zeta 6-31G basis set was used through the Gaussian 98
package on an Athlon processor using the Windows 98 Second Edition operating
system. Full geometry optimizations were calculated on all of the structures
without symmetry restrictions.
Transition states were found using the QST3 algorithm by means of searching
one and only one imaginary frecuency. In order to rationalize the isomerization
process the property considered in this work was the electronic potential energy,
V. V The energy values are given in atomic units called hartrees, so to obtain results
in kcal mol -1 , energy values must be multiplied by 627.5095.
© c+b 3/04