Does the Intramolecular Hydrogen Bond Affect the Spectroscopic Properties of Bicyclic Diazole Heterocycles?

Table 1

Selected bond lengths of pyrrolo[1,2-a]pyrazin-1(2H)-ones (1–22), optimized at the B3LYP/aug-cc-pVDZ level of theory, HOMA indices, and calculated C=C and C=O stretching frequencies.

Compound	3,4-Dihydropyrrolopyrazinones	Pyrrolopyrazinones	Bond length [Å]						Pyrrole ring			Calculated; B3LYP/aug-cc-pVDZ	Calculated; B3LYP/aug-cc-pVDZ
	Pyrrole ring		N5C9	C9C8	C8C7	C7C6	C6N5		HOMA	EN	GEO		νC=C (cm^−1); Pyrrole ring stretching vibrations
1	Pyrrole		1.376	1.383	1.428	1.382	1.376		0.833	0.071	0.096		1568
1a	R2 = CH3, R3 = H		1.383	1.390	1.418	1.390	1.383		0.876	0.082	0.043		1578
1b	R2 = CH2Cl, R3 = H		1.384	1.392	1.416	1.391	1.384		0.882	0.082	0.036		1575
1c	R2 = CHCl2, R3 = H		1.385	1.393	1.414	1.392	1.384		0.885	0.082	0.032		1573
2		R2 = CH3, R3 = H	1.396	1.390	1.416	1.390	1.396		0.848	0.097	0.055		1564
3		R2 = CH2Cl, R3 = H	1.396	1.391	1.415	1.390	1.396		0.852	0.095	0.053		1567
4		R2 = CHCl2, R3 = H	1.389	1.393	1.413	1.393	1.388		0.875	0.091	0.034		1565
5		R2 = CH3, R3 = Cl	1.394	1.391	1.415	1.391	1.393		0.859	0.095	0.046		1562
6		R2 = CH2Cl, R3 = Cl	1.393	1.392	1.414	1.391	1.393		0.862	0.093	0.045		1565
7		R2 = CHCl2, R3 = Cl	1.391	1.392	1.413	1.392	1.391		0.869	0.091	0.039		1564
8		R2 = CH3, R3 = NH2	1.391	1.395	1.412	1.395	1.390		0.873	0.098	0.029		1555
9		R2 = CH2Cl, R3 = NH2	1.390	1.394	1.412	1.394	1.390		0.875	0.095	0.030		1560
10		R2 = CHCl2, R3 = NH2	1.389	1.397	1.409	1.397	1.388		0.883	0.096	0.021		1555
11		R2 = CH3, R3 = CH3	1.392	1.392	1.415	1.391	1.391		0.863	0.095	0.042		1564
12		R2 = CH2Cl, R3 = CH3	1.391	1.392	1.392	1.392	1.391		0.905	0.053	0.042		1567
13		R2 = CHCl2, R3 = CH3	1.389	1.393	1.413	1.393	1.388		0.875	0.091	0.034		1565
14		R2 = CH3, R3 = CH2CH2CH2Cl	1.390	1.392	1.415	1.391	1.390		0.865	0.093	0.042		1565
15		R2 = CH2Cl, R3 = CH2CH2CH2Cl	1.390	1.392	1.414	1.391	1.389		0.868	0.091	0.041		1568
16		R2 = CHCl2, R3 = CH2CH2CH2Cl	1.387	1.393	1.413	1.392	1.387		0.876	0.089	0.035		1567
17		R2 = CH3, R3 = CH2CH2CH2NH2	1.390	1.392	1.415	1.392	1.390		0.864	0.095	0.040		1561
18		R2 = CH2Cl, R3 = CH2CH2CH2NH2	1.390	1.392	1.414	1.392	1.389		0.869	0.092	0.039		1567
19		R2 = CHCl2, R3 = CH2CH2CH2NH2	1.388	1.393	1.413	1.393	1.387		0.877	0.090	0.033		1565
20		R2 = CH3, R3 = CH2CH2CH2NHC(NH)NH2	1.390	1.392	1.415	1.391	1.390		0.865	0.094	0.042		1564
21		R2 = CH2Cl, R3 = CH2CH2CH2NHC(NH)NH2	1.390	1.392	1.414	1.392	1.390		0.869	0.092	0.040		1568
22		R2 = CHCl2, R3 = CH2CH2CH2NHC(NH)NH2	1.387	1.393	1.413	1.393	1.387		0.877	0.089	0.034		1566
	Pyrazinone ring		C1N2	N2C3	C3-C4	C4N5	N5C9	C9C1	HOMA	EN	GEO	νC=O (cm^−1)	Pyrazine νC=C stretching vibrations(cm^−1)
1a	R2 = CH3, R3 = H		1.390	1.462	1.525	1.453	1.383	1.470				1705
1b	R2 = CH2Cl, R3 = H		1.404	1.467	1.525	1.455	1.384	1.463				1721
1c	R2 = CHCl2, R3 = H		1.414	1.468	1.524	1.456	1.385	1.459				1726
1d	Pyrazine		1.338	1.338	1.400	1.338	1.338	1.400	0.985	0.010	0.005	—	1617
1e	2-Oxo-pyrazine		1.400	1.367	1.364	1.374	1.303	1.469	0.591	0.087	0.322	1743	1645
2		R2 = CH3, R3 = H	1.406	1.388	1.349	1.391	1.396	1.456	0.466	0.199	0.335	1721	1695
3		R2 = CH2Cl, R3 = H	1.421	1.396	1.346	1.392	1.396	1.452	0.414	0.209	0.376	1738	1705
4		R2 = CHCl2, R3 = H	1.440	1.419	1.351	1.391	1.389	1.442	0.408	0.251	0.341	1741	1703
5		R2 = CH3, R3 = Cl	1.420	1.390	1.351	1.390	1.394	1.450	0.470	0.210	0.320	1726	1686
6		R2 = CH2Cl, R3 = Cl	1.435	1.400	1.348	1.391	1.393	1.447	0.416	0.224	0.360	1745	1694
7		R2 = CHCl2, R3 = Cl	1.446	1.406	1.349	1.389	1.391	1.443	0.402	0.234	0.364	1744	1690
8		R2 = CH3, R3 = NH2	1.415	1.396	1.358	1.396	1.391	1.448	0.512	0.234	0.254	1734	1695
9		R2 = CH2Cl, R3 = NH2	1.431	1.407	1.354	1.396	1.390	1.445	0.444	0.250	0.306	1748	1711
10		R2 = CHCl2, R3 = NH2	1.445	1.414	1.356	1.395	1.389	1.438	0.440	0.268	0.292	1750	1703
11		R2 = CH3, R3 = CH3	1.411	1.401	1.354	1.392	1.392	1.451	0.487	0.225	0.288	1726	1693
12		R2 = CH2Cl, R3 = CH3	1.427	1.411	1.351	1.393	1.391	1.447	0.429	0.239	0.332	1742	1708
13		R2 = CHCl2, R3 = CH3	1.440	1.419	1.351	1.391	1.389	1.442	0.408	0.251	0.341	1741	1703
14		R2 = CH3, R3 = CH2CH2CH2Cl	1.413	1.404	1.355	1.392	1.390	1.450	0.488	0.229	0.282	1723	1692
15		R2 = CH2Cl, R3 = CH2CH2CH2Cl	1.428	1.414	1.352	1.392	1.390	1.446	0.432	0.243	0.325	1740	1705
16		R2 = CHCl2, R3 = CH2CH2CH2Cl	1.441	1.422	1.352	1.391	1.387	1.442	0.407	0.255	0.339	1740	1700
17		R2 = CH3, R3 = CH2CH2CH2NH2	1.411	1.403	1.356	1.390	1.390	1.451	0.495	0.229	0.276	1715	1683
18		R2 = CH2Cl, R3 = CH2CH2CH2NH2	1.428	1.415	1.350	1.393	1.390	1.446	0.423	0.240	0.337	1740	1705
19		R2 = CHCl2, R3 = CH2CH2CH2NH2	1.441	1.423	1.351	1.391	1.388	1.441	0.400	0.253	0.347	1739	1699
20		R2 = CH3, R3 = CH2CH2CH2NHC(NH)NH2	1.412	1.405	1.355	1.392	1.390	1.450	0.487	0.229	0.284	1723	1691
21		R2 = CH2Cl, R3 = CH2CH2CH2NHC(NH)NH2	1.428	1.414	1.351	1.393	1.390	1.446	0.427	0.243	0.330	1741	1706
22		R2 = CHCl2, R3 = CH2CH2CH2NHC(NH)NH2	1.441	1.423	1.352	1.391	1.387	1.441	0.404	0.256	0.340	1740	1700