Chemistry Reference
In-Depth Information
TABLE 4.12. Relative Yields of Individual Radicals (
G
rel
), Overall, and Partial Rate
Constants (
k
, /M/s) for the Reaction of
•
OH in H
2
O or
•
OD in D
2
O with Gly and
Deuterated Gly Anions. Estimated Uncertainty
±
10% for
k
overall
and
G
rel
and
±
14%
for
k
Values
glycyl
Aminoethyl
Aminyl
N-Attack
Solute
G
rel
G
rel
G
rel
G
rel
(Solvent)
k
overall
k
k
k
k
NH
2
-cH
2
-cOO
−
0.37
0.22
0.41
0.63
(H
2
O)
2.8 × 10
9
1.0 × 10
9
0.62 × 10
9
1.2 × 10
9
1.8 × 10
9
NH
2
-cD
2
-cOO
−
0.30
0.26
0.44
0.70
(H
2
O)
2.8 × 10
9
0.63 × 10
9
0.55 × 10
9
0.92 × 10
9
1.5 × 10
9
ND
2
-cH
2
-cOO
−
0.36
0.25
0.39
0.64
2.1 × 10
9
0.76 × 10
9
0.53 × 10
9
0.82 × 10
9
1.4 × 10
9
ND
2
-cD
2
-cOO
−
0.24
0.26
0.50
0.76
1.6 × 10
9
0.38 × 10
9
0.42 × 10
9
0.80 × 10
9
1.2 × 10
9
Adapted from Štefanić et al. [294].
(Table 4.12). The results clearly demonstrate that majority of the reactions of
•
OH and
•
OD occurred by the interactions with the amino group of the glycine
anion (Table 4.12). In this interaction, decarboxylation and aminomethyl
radical formation contributed to ≈25%. The remaining percentage led to the
formation of the aminyl radical (reactions c and e in Fig. 4.24).
The values of
k
H
/
k
D
for the appropriate couples of gly anions are given in
Table 4.13 [294]. The values varied from 1.6 to 2.0 in H
2
O and D
2
O, respec-
tively, and were similar to the values determined for the abstraction of H/D
from the α-c-H(D) bond in ethanol and methylamine by the
•
OH radical in
H
2
O [303]. The secondary KIEs of the deuterated amino group for abstraction
from the −cH
2
(cD
2
)- group were relatively high (1.3-1.7), suggesting
•
OH and
•
OD as reactants and/or H
2
O and D
2
O as solvents. The primary KIE increased
to as high as 2.6 for gly
−
+
•
OH in H
2
O versus all-deuterated gly
−
+
•
OD in
D
2
O. comparatively, the KIE decreased to as low as 1.2 for ND
2
-cH
2
-
cOO
−
+
•
OD in D
2
O versus NH
2
-cD
2
-cOO
−
+
•
OH in H
2
O.
Values for the formation of the aminyl radical were determined in the
range of 1.1-1.5 for all effects (Table 4.13). These values were similar to
the secondary KIE of 1.1, obtained for the H-atom abstraction by
•
OH from
the −NH
2
group of cH
3
NH
2
or cD
3
NH
2
in H
2
O [303]. However, the amino-
ethyl radical formation showed a positive KIE for all, except one couple.
Overall, it appears from the results of KIE that the process of heterogeneous
c−c bond rupture to form cO
2
and the aminomethyl radicals may be sensi-
tive to the electron density at the nitrogen, stability of the solvent cage, stabil-
ity of the 3-e-bonded intermediate, and thermodynamic stabilities of the
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