double and the three single bonds, two hydrogenated basins and four monosynaptic
basins, located two on each oxygen atom. The annihilation of the disynaptic basin V
(C2,O4) is observed in the turning point between SSD-I and SSD-II by means of a
fold-type catastrophe, and in this way the topological analysis describes the beginning of the three-membered ring opening. The second topological change of the ELF
field connecting SSD-II and SDD-III corresponds to a cusp-type catastrophe where
two monosynaptic basins V 1,2 (O1) merging to form a unique V(O1) monosynaptic
basin. Then the bonding basin V(C2,C3) becomes monosynaptic V(C2) by means of
a fold-type catastrophe (just at the TS of the process, as can be seen in Fig. 10.9) and
the SSD-IV is reached. From that point on, the two fragments separate from each
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-4
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
Total Energy (Hartree)
Reaction Coordinate (amu 1/2 bohr)
SSD-I
SSD-II
SSD-III SSD-IV
SSD-V
SSD-VI
Fig. 10.9 Energy profile for the α-lactone (left side) decomposition to obtain carbon monoxide
plus formaldehyde through TS4, calculated by means of the IRC method. The SSDs found are
indicated
C 3
C 2
O 4
O 1
H 9
H 8
SSD-I
C 3
C 2
O 4
O 1
H 9
H 8
SSD-II
C 3
C 2
O 4
O 1
H 9
H 8
SSD-III
C 3
C 2
O 4
O 1
H 9
H 8
SSD-IV
C 3
C 2
O 4
O 1
H 9
H 8
SSD-V
C 3
C 2
O 4
O 1
H 9
H 8
SSD-VI
Scheme 10.3 Representation of the second step of the glycolic acid decomposition through the
mechanism A, depicted from the ELF viewpoint
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J. Andrés et al.