Vibrational Spectroscopic Study of the Cocrystal Products Formed by Cinchona Alkaloids with 5-Nitrobarbituric Acid

Table 3

Assignments of the major bands in the fingerprint region of the infrared absorption spectra of 5-nitrobarbituric acid, cinchonidine, and their 1 : 1 cocrystal product.

Assignment	Nitrobarbituric (cm^−1)	Cocrystal (cm^−1)	Cinchonidine (cm^−1)	Assignment
Carbonyl out-of-plane bending mode	779	762
C–N ring deformation mode	1246	1256
		Obscured and not observed	1352	Nonprotonated quinuclidine mode
Nitro group symmetric stretching mode	1381	1358
		Obscured and not observed	1568	Nonprotonated quinoline mode
2-CO stretching mode	1614	1595
4,6-CO antisymmetric mode	1651	1666
4,6-CO symmetric mode	1705	1691