Combined FTIR Matrix Isolation and Density Functional Studies of Indole-3-Pyruvic Acid Molecule. Spectroscopic Evidence of Gas-Phase Tautomerism
Table 1
Relative stability (a) and gas-phase population at 380 K of the hydroxylic (H) and ketonic (K) forms of IPA molecule.
Tautomer
Population (%)
H01
0.0
0.0
0.0
24.1
K02
1.0
1.0
0.6
40.5
K03
5.7
5.8
5.4
13.1
K04
8.4
8.9
8.55
9.0
H05
10.75
11.2
11.3
1.1
K06
10.8
11.3
11.0
4.6
K07
11.6
12.1
11.8
2.9
H08
12.8
13.0
13.0
0.9
K09
13.85
14.4
14.1
1.6
K10
18.3
19.0
18.7
0.4
K11
19.4
20.4
20.1
0.7
K12
23.0
23.6
23.6
0.05
K13
26.1
26.9
26.7
0.2
K14
26.1
26.9
26.6
0.1
K15
30.3
30.4
30.1
0.0
K16
30.8
29.2
28.6
0.0
H17
31.8
32.2
32.2
0.0
H18
33.3
31.0
30.25
0.0
H19
40.15
40.8
40.8
0.0
H20
41.8
42.7
40.8
0.0
H21
41.6
42.7
42.9
0.0
The G2MP2 energy difference values (kJ mol−1) are calculated with respect to the lowest energy tautomer H01 and include zero-point vibrational () and thermal plus zero-point vibrational energy ( and ) corrections.
