NH Stretching Frequencies of Intramolecularly Hydrogen-Bonded Systems: An Experimental and Theoretical Study

Abstract

The vibrational NH stretching transitions in secondary amines with intramolecular NH···O hydrogen bonds were investigated by experimental and theoretical methods, considering a large number of compounds and covering a wide range of stretching wavenumbers. The assignment of the NH stretching transitions in the experimental IR spectra was, in several instances, supported by measurement of the corresponding ND wavenumbers and by correlation with the observed NH proton chemical shifts. The observed wavenumbers were correlated with theoretical wavenumbers predicted with B3LYP density functional theory, using the basis sets 6-311++G(d,p) and 6-31G(d) and considering the harmonic as well as the anharmonic VPT2 approximation. Excellent correlations were established between observed wavenumbers and calculated harmonic values. However, the correlations were non-linear, in contrast to the results of previous investigations of the corresponding OH···O systems. The anharmonic VPT2 wavenumbers were found to be linearly related to the corresponding harmonic values. The results provide correlation equations for the prediction of NH stretching bands on the basis of standard B3LYP/6-311++G(d,p) and B3LYP/6-31G(d) harmonic analyses, with standard deviations close to 38 cm−1. This is significant because the full anharmonic VPT2 analysis tends to be impractical for large molecules, requiring orders of magnitude more computing time than the harmonic analysis.

Multistimuli-responsive multicolor solid-state luminescence tuned by NH-dependent switchable hydrogen bonds

“…Only one Cl–O stretching vibration absorption occurs at 1101 cm −1 for ground 1a , 19,47,63 which is due to the Cl–O bond equivalence caused by the breaking of NH bpmtzH ⋯OClO 3 − hydrogen bonds, implying that luminescence mechanochromism originates from the breaking of NH bpmtzH ⋯OClO 3 − hydrogen bonds. Moreover, luminescence vapochromism and mechanochromism are related to NH dppa ⋯O solvent and NH bpmtzH ⋯OClO 3 − hydrogen bonds, respectively, which are also supported by changes in the shape and wavenumber of the N–H bending vibration absorptions ( δ N–H , 1530–1600 cm −1 ) 64–66 and the wavenumber and strength of the N–H stretching vibration absorptions ( υ N–H , 3105–3280 cm −1 ) 67–69 of 1a (Fig. S8†) and are also well confirmed by changes in the FT-IR spectra of 1b–1d in different solid states (Fig.…”

Recruitment of hexahydroquinoline as anticancer scaffold targeting inhibition of wild and mutants EGFR (EGFR WT , EGFR T790M , and EGFR L858R )

“…Regarding the 13 C NMR spectra, the appearance of a peak in the range of 33.19–36.85 ppm is associated with the carbon atom at position 4 in the HHQ ring. In addition, the disappearance of the peaks at 100–120 ppm for the nitrile of ethyl cyanoacetate 46–48 and 190–220 ppm for the carbonyl of the aldehyde 49 was reported and supported by IR spectra, where the peaks at 2300–2250 cm −1 (nitrile of ethyl cyanoacetate) 50 and 3200–3100 cm −1 (NH of intermediates 3a–c ) were vanished 51 . The molecular weights of target compounds and the mass spectroscopy results were compatible.…”

In silico evaluation of a new compound incorporating 4(3H)-quinazolinone and sulfonamide as a potential inhibitor of a human carbonic anhydrase

“…The literature reports that the N–H stretching vibration can be found in the IR spectra at 3300–3500 cm −1 [ 34 ]. Two symmetric and two asymmetric (N–H) stretching vibrations were detected at 3463.09, 3447.88, 3351.47, and 3344.65 cm −1 , respectively.…”