reaction products, namely, carbon monoxide, water and formaldehyde. In
Fig. 10.15 we report the energy profile along the IRC path down from TS3 to the
glycolic acid on one side, and to the reaction products in the other side. The SSDs
found are indicated and sketched in Scheme 10.5.
As can be seen, the process begins in a different way than in the A and B
mechanisms: although the first topological change also corresponds to a new V(O1)
monosynaptic basin appearance, the proton transfer does not begin neither in the
first stage of the process nor in the second or the third. It is not until SSD-IV is
reached that the V(O5,H7) splits into two monosynaptic basins V(O5) and V(H7).
This can also be viewed in Fig. 10.16, in which the snapshots of the ELF basins for
some selected points along the IRC for the decomposition of the glycolic acid by
means of the mechanism C are reported. As can be seen, the snapshots (a), (b) and
(c) do not show any proton transfer.
The breaking of the C2–O1 bond can be sensed by comparing the snapshots
(b) and (c) in Fig. 10.16: the green disynaptic basin between C2 and O1 cannot be
detected at SSD-III. The proton transfer can be followed in the snapshots (c), (d),
(e), and (f) in Fig. 10.16. The C2–C3 breaking is reflected by the red monosynaptic
V(C2) basin that can be seen at Fig. 10.16g instead of the former disynaptic V(C2,
C3) green basin between these two atoms that can still be viewed at Fig. 10.16f.
Therefore, the series of chemical events taking place according to the ELF
description is rather different in the mechanism C with respect the other two
mechanisms: in the mechanism C the C2–O1 bond breaks first, forming an OH
moiety. After that, at the turning point between SSD-III and SSD-IV, the V(H7)
appears accounting from the proton migration from O5 to O1 while at the turning
point between SSD-V and SSD-VI the bonding basin V(O1,H7) appears. After that,
going down from the TS to the final products, the chemical events taking place are:
(i) the C2–C3 breaking, (the disynaptic basin V(C2,C3) becomes monosynaptic V
(C2)) (ii) the disynaptic basin V 1 (C3,O5) splits into two disynaptic basins V 1,2 (C3,
O5) accounting for the double bond formation.
In the mechanism A the H6 transfer from O1 to O5 was the first chemical event
taking place, followed by the C3–O5 breaking (water departure), lactone ring
closure through C3–O4 bond formation, and decomposition of the lactone intermediate via C2–O4 bond breaking followed by C2–C3 breaking and final C3–O4
double bond formation. On the other hand, in the mechanism B the series of events
begun with the H6 departure from O1 followed by the C3–O5 breaking (OH
departure), water formation via O5–H6 bond, closure of the lactone ring through
C3–O1 bond formation, and decomposition of the lactone intermediate via C2–O1
bond breaking followed by C2–C3 breaking and final C3–O1 double bond
formation.
The population evolution of several basins, related with the advance of the
process along the mechanism C, have been represented as a function of the reaction
coordinate in Fig. 10.17, in which the SSDs found are also indicated.
Along SSD-I only a diminution of the V(C2,O1) population concomitant with an
increase in the V(O1) basins population is sensed. At the turning point between
SSD-I and SSD-II a new monosynaptic basin appears on O1, and this is reflected in
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Fig. 10.15 we report the energy profile along the IRC path down from TS3 to the
glycolic acid on one side, and to the reaction products in the other side. The SSDs
found are indicated and sketched in Scheme 10.5.
As can be seen, the process begins in a different way than in the A and B
mechanisms: although the first topological change also corresponds to a new V(O1)
monosynaptic basin appearance, the proton transfer does not begin neither in the
first stage of the process nor in the second or the third. It is not until SSD-IV is
reached that the V(O5,H7) splits into two monosynaptic basins V(O5) and V(H7).
This can also be viewed in Fig. 10.16, in which the snapshots of the ELF basins for
some selected points along the IRC for the decomposition of the glycolic acid by
means of the mechanism C are reported. As can be seen, the snapshots (a), (b) and
(c) do not show any proton transfer.
The breaking of the C2–O1 bond can be sensed by comparing the snapshots
(b) and (c) in Fig. 10.16: the green disynaptic basin between C2 and O1 cannot be
detected at SSD-III. The proton transfer can be followed in the snapshots (c), (d),
(e), and (f) in Fig. 10.16. The C2–C3 breaking is reflected by the red monosynaptic
V(C2) basin that can be seen at Fig. 10.16g instead of the former disynaptic V(C2,
C3) green basin between these two atoms that can still be viewed at Fig. 10.16f.
Therefore, the series of chemical events taking place according to the ELF
description is rather different in the mechanism C with respect the other two
mechanisms: in the mechanism C the C2–O1 bond breaks first, forming an OH
moiety. After that, at the turning point between SSD-III and SSD-IV, the V(H7)
appears accounting from the proton migration from O5 to O1 while at the turning
point between SSD-V and SSD-VI the bonding basin V(O1,H7) appears. After that,
going down from the TS to the final products, the chemical events taking place are:
(i) the C2–C3 breaking, (the disynaptic basin V(C2,C3) becomes monosynaptic V
(C2)) (ii) the disynaptic basin V 1 (C3,O5) splits into two disynaptic basins V 1,2 (C3,
O5) accounting for the double bond formation.
In the mechanism A the H6 transfer from O1 to O5 was the first chemical event
taking place, followed by the C3–O5 breaking (water departure), lactone ring
closure through C3–O4 bond formation, and decomposition of the lactone intermediate via C2–O4 bond breaking followed by C2–C3 breaking and final C3–O4
double bond formation. On the other hand, in the mechanism B the series of events
begun with the H6 departure from O1 followed by the C3–O5 breaking (OH
departure), water formation via O5–H6 bond, closure of the lactone ring through
C3–O1 bond formation, and decomposition of the lactone intermediate via C2–O1
bond breaking followed by C2–C3 breaking and final C3–O1 double bond
formation.
The population evolution of several basins, related with the advance of the
process along the mechanism C, have been represented as a function of the reaction
coordinate in Fig. 10.17, in which the SSDs found are also indicated.
Along SSD-I only a diminution of the V(C2,O1) population concomitant with an
increase in the V(O1) basins population is sensed. At the turning point between
SSD-I and SSD-II a new monosynaptic basin appears on O1, and this is reflected in
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