Combined FTIR Matrix Isolation and Density Functional Studies of Indole-3-Pyruvic Acid Molecule. Spectroscopic Evidence of Gas-Phase Tautomerism

Table 4

Theoretical B3PW91/6-311++G** frequencies (cm⁻¹) of H01 tautomer calculated for the free molecule and the molecule in its crystal phase.

Free molecule	Crystal molecule	DRIFT	Approximate description
3805	3688	3433	νOH
3704	3498	3411	νOH
3686	3682	3453	νNH
3288	3280		νCH
3216	3225		νCH
3202	3203		νCH
3191	3193		νCH
3181	3183		νCH
3174	3176		νCH
1758	1737	1704.7	νC=O/νC=C
1712	1705	1648.1	νC=C/νC=O
1672	1672		νRing
1630	1629		νRing
1570	1563	1523.7	νRing/δ ipNH
1529	1529		νRing/δ ipNH/δ ipCH
1489	1488		νRing/δ ipCH
1471	1465	1457	δ ipNH/νRing/δ ipCOH/δ ipCH
1435	1443	1427.6	δ ipCH/δ ipCOH
1414	1414	1421.9	δ ipCH/νRing/δ ipCOH/δ ipNH
1388	1388	1378.9	δ ipCH/νRing/δ ipNH/δ ipCOH
1349	1349		νRing/δ ipCH/δ ipCOH
1346	1337	1336.9	δ ipCOH/δ ipCH/νRing /νCOH
1313	1288	1289.7	δ ipCOH/νRing/δ ipCH/νCOH
1268	1267		δ ipCH/δ ipNH/νRing
1257	1254	1245.8	δ ipCH/νRing/δ ipCOH
1183	1233	1212.8	νCOH/δ ipCOH νCC/δ ipCH
1174	1175	1129.4	δ ipCH/δ ipCOH/νRing
1154	1154	1106.7	δ ipCH/νRing
1130	1143		νCOH/δ ipCH/δ ipNH
1122	1123		δ ipCH/δ ipNH/νRing/νCOH
1085	1080	1060.7	νRing/δ ipRing
1040	1039	1010.1	νRing/δ ipRing
972	977	925.5	δ opCH
937	940		δ opCH
892	903		δ ipRing
884	887	884.2	δ ipRing
888	879	874.6	δ opCH
853	853	858.4	δ opCH
839	841	832.6	δ opCH
818	821		δ ipRing
773	779	755.7	δ opRing
767	768	750.3	δ ipRing
751	751		δ opCH
678	660	702.3	δ ipRing
646	627	633.0	δ opRing
612	610	612.1	δ ipRing
586	585	580.9	δ opRing/δ opNH/δ opCOH
561	562		δ ipRing
527	540	537	δ opCOH
513	528	530	δ ipRing
488	526	516.0	δ opCOH
464	466	459.0	δ ipRing
462	462	422.3	δ opNH