Structural, Electronic, and Vibrational Properties of Isoniazid and Its Derivative N-Cyclopentylidenepyridine-4-carbohydrazide: A Quantum Chemical Study

Table 2

Comparison of the observed and calculated vibrational spectra of isoniazid with (B3LYP)/6-311 G (d, p) and B3LYP/LANL2DZ.

B3LYP				FTIR (exp.)	FT Raman (exp.)	Vibrational assignments
LANL2DZ	IR (Int.)	6-311 G (d, p)	IR (Int.)
27	4.4893	39	2.1136	—	—	Whole molecule twists from joint
136	0.1522	121	3.0144	—	—	Twist NH2
163	0.0223	134	2.9603	—	—	Rock NH2
200	2.6928	198	2.2873	—	—	Whole molecule bends from joint
281	9.3909	261	15.6415	—	—	𝛽(C–N–N)
343	64.239	306	54.4552	—	—	Twist NH2
380	4.8231	370	2.1727	—	—	𝜏(C–C–C=O)
385	3.0767	377	0.0835	—	—	𝛾(C–C–C) + 𝛾(C–C–H)
457	3.736	452	5.6374	504	504	𝛾(C–C–C) + 𝛾(C–C–H)
528	2.5885	544	17.1188	—	—	Rock NH2 + 𝛽(C–C=O)
578	142.03	588	52.8091	—	—	Rock NH2
658	23.445	636	26.3687	660	666	𝜏(C–C–C–C) + 𝜏(C–N–C–C)
659	28.530	659	0.79			Twist NH2
668	162.33	702	45.9836	674	682	Rock NH2
701	110.45	720	3.2826	—	—	𝛾(C–N–H)
710	0.1352	745	774.0493	—	—	𝛽(C–N–C) + 𝛽(C–C–C)
758	29.601	836	13.6245	745	750	𝛾(C–C–C) + 𝛾(C–C–H)
854	37.843	865	0.5422	845	849	𝛾(C–C–H)
904	0.0237	874	143.4664	—	—	𝛾(C–C–H)
953	4.925	956	0.4745	—	—	Ring breathing
998	2.1689	970	3.0528	—	—	𝛾(C–C–H)
1005	2.381	977	3.1906	1020	1002	𝛾(C–C–H)
1046	9.4117	1052	17.7683			𝛽(C–C–H) + 𝛽(C–C=O)
1049	20.656	1060	5.0938	1061	1057	𝛽(C–N–C) + 𝛽(C–C–C)
1072	1.5593	1071	3.1435	—	—	𝛽(C–C–H)
1170	69.756	1154	50.7026	—	—	𝛽(C–C–C) + 𝛽(C–C–H)
1200	1.2477	1198	1.8033	1200	1187	𝛽(C–C–H)
1223	0.006	1227	3.1093	—	—	Twist NH2
1249	5.3368	1268	3.7348	—	—	𝜈(C–N) + 𝜈(C–C)
1305	3.9465	1301	3.2532	—	—	𝛽(C–C–H)
1353	177.39	1334	194.7891	1334	1331	𝛽(O=C–N) + 𝛽(C–C–H)
1383	56.249	1386	31.6275	—	—	𝛽(C–C–H)
1416	48.473	1427	19.6455	1412	1410	𝛽(C–N–H)
1448	2.1058	1465	1.3185	—	—	𝛽(C–C–H)
1517	56.958	1535	28.9279	1472	—	𝜈(C–C)
1560	11.455	1574	9.7845	—	—	𝜈(C–C)
1577	87.192	1634	30.7552	1556	1551	𝜈(C=O)
1642	55.629	1684	235.7803	1635	1642	S(NH2)
3079	32.086	3030	34.8746	3050	3065	𝜈(C–H)
3085	9.0201	3035	14.6458	—	—	𝜈(C–H)
3121	4.9876	3089	2.9337	—	—	𝜈(C–H)
3153	8.4279	3119	3.3617	—	—	𝜈(C–H)
3381	1.8185	3341	1.8712	—	—	𝜈(N–H)
3389	17.234	3387	16.6022	3303	3300	𝜈(N–H)
3509	9.0098	3426	4.449	—	—	𝜈(N–H)

𝜈: stretching; 𝛽: in plane bending; 𝛾: out of plane bending; S: scissoring; w: wagging; 𝜏: torsion.