Effects of Dynamical Couplings in IR Spectra of the Hydrogen Bond inN-Phenylacrylamide Crystals

Abstract

This article presents the investigation results of the polarized IR spectra of the hydrogen bond in N-phenylacrylamide crystals measured in the frequency range of the proton and deuteron, ν(N-H) and ν(N-D), stretching vibration bands. The basic spectral properties of the crystals were interpreted quantitatively in terms of the "strong-coupling" theory. The proposed model of the centrosymmetric dimer of hydrogen bonds facilitated the explanation of the well-developed, two-branch structure of the ν(N-H) and ν(N-D) bands as well as the isotopic dilution effects in the spectra. The vibronic mechanism of the generation of the long-wave branch of the ν(N-H) band ascribed to the excitation of the totally symmetric proton vibration was elucidated. The complex fine structure pattern of ν(N-H) and ν(N-D) bands in N-phenylacrylamide spectra in comparison with the spectra of other secondary amide crystals (e.g., N-methylacetamide and acetanilide) can be accounted for in terms of the vibronic model for the forbidden transition breaking in the dimers. On the basis of the linear dichroic and temperature effects in the polarized IR spectra of N-phenylacrylamide crystals, the H/D isotopic "self-organization" effects were revealed.

Elucidating the Davydov-coupling mechanism in hydrogen bond dimers: Experimental and theoretical investigation of the polarized IR spectra of 3-thiopheneacetic and 3-thiopheneacrylic acid crystals.

“…Surprisingly, the vibronic mechanism appeared to be also effective in the generation of IR spectra of crystals with infinitely long chains of hydrogen bonded molecules in their lattices, e.g., N-methylthioacetamide [44] or N-phenylacrylamide [74] crystals. The H/D isotopic effects in their spectra were found fairly similar to the analogous isotopic effects in the corresponding spectra of the N -H…S bonded cyclic dimers.…”

Synthon identification in co-crystals and polymorphs with IR spectroscopy. Primary amides as a case study

“…In crystals with chains of H-bonded systems as for example the amide dimer, the IR spectrum can give rise to spectacular variations. 33 The observed diversity in the spectral behavior of amide crystals is strongly dependent on the electronic structure of amide molecules, which is again modified by substituent groups linked to the amide fragment of the molecules. The N-H stretching absorptions of primary amides like benzamide that crystallize with the amide dimers linked in a ladder like chain show bands at 3370 cm 21 and 3178 cm 21 corresponding to the asymmetric and symmetric stretch.…”

Temperature and H/D Isotopic Effects in the IR Spectra of the Hydrogen Bond in Solid-State 2-Furanacetic Acid and 2-Furanacrylic Acid

“…On the other hand, the ν N−D bands are extremely narrow as practically devoid of the forbidden band branch [37,39]. The vibronic mechanism is also effective in the generation of IR spectra of crystals with infinite open chains of hydrogen bonded molecules, for example, N-methylthioacetamide [42] or Nphenylacrylamide [52] crystals. Also the H/D isotopic effects in their spectra are fairly similar to the analogous isotopic effects in the corresponding spectra of the N-H• • • S bonded cyclic dimers.…”