the SSD-I ends up with the departure of the H6 from O1, where the bonding basin
V(O1,H6) splits into two monosynaptic basins V(O1) and V(H6). After that, the
proton is located between the monosynaptic basins of O1 and O5 along SSD-II and
SSD-III, finally reaching the O5 atom at SSD-IV. However, in the mechanism B the
breaking of the C3–O5 bond takes place earlier than in the mechanism A according
to the BET description: in the turning point between SSD-II and SSD-III the V(C3,
O5) disynaptic basin is replaced by a new V(O5) monosynaptic basin. In the
mechanism A this change took place once the H6 had reached the O5 atom,
-303.5
-303.48
-303.46
-303.44
-303.42
-303.4
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
7
Total Energy (Hartree)
Reaction Coordinate (amu
1/2 bohr)
SSD-I
SSD-II
SSD-III
SSD-IV
SSD-V
SSD-VI
Fig. 10.12 Energy profile for the water elimination from glycolic acid (left side) to obtain the
α-lactone intermediate through TS2, calculated by means of the IRC method. The SSDs found are
indicated
O 5
C 3
C 2
O 4
O 1
H 6
H 9
H 8
H 7
SSD-I
O 5
C 3
C 2
O 4
O 1
H 6
H 9
H 8
H 7
SSD-II
O 5
C 3
C 2
O 4
O 1
H 6
H 9
H 8
H 7
SSD-III
O 5
C 3
C 2
O 4
O 1
H 6
H 9
H 8
H 7
SSD-IV
O 5
C 3
C 2
O 4
O 1
H 6
H 9
H 8
H 7
SSD-V
O 5
C 3
C 2
O 4
O 1
H 6
H 9
H 8
H 7
SSD-VI
Scheme 10.4 Representation of the first step of the glycolic acid decomposition through the
mechanism B, depicted from the ELF viewpoint
10 Quantum Chemical Topology Approach …
279