TY - JOUR

T1 - Raman spectra of crystalline secondary amides

AU - Kolesov, Boris A.

N1 - Copyright © 2017 Elsevier B.V. All rights reserved.

PY - 2017/5/15

Y1 - 2017/5/15

N2 - We present a Raman-spectroscopic study of secondary amides (acetanilide, methacetin, phenacetine, orthorhombic and monoclinic polymorphs of paracetamol) as well as simple amides formanilide and benzanilide. The study was carried out on single crystals and in the temperature range of 5–300 K. The series of compounds with the same molecular fragment - acetamide group – can serve as a model system to study the interrelation between this group and the properties of the intermolecular “peptide-type” NH ⋯ O[dbnd]C hydrogen bonds. For all of the “acetamide family” of the compounds, similar changes in the Raman spectra were observed upon cooling of the samples: emergence of new Amide I(−) and Amide I(+) bands, which are red and blue shifted, respectively, from the conventional Amide-I band by around of 5–10 cm− 1. Corresponding changes in the same temperature range were observed for the N[sbnd]H out-of-plane bending (Amide V) and N[sbnd]H stretching vibrations of the N[sbnd]H ⋯ O[dbnd]C hydrogen bond. All of the spectral changes observed upon cooling of the samples can be presumed to result from a delocalization of the Amide-I and N[sbnd]H modes and appearance of dynamical (Davydov's) splitting at low temperature.

AB - We present a Raman-spectroscopic study of secondary amides (acetanilide, methacetin, phenacetine, orthorhombic and monoclinic polymorphs of paracetamol) as well as simple amides formanilide and benzanilide. The study was carried out on single crystals and in the temperature range of 5–300 K. The series of compounds with the same molecular fragment - acetamide group – can serve as a model system to study the interrelation between this group and the properties of the intermolecular “peptide-type” NH ⋯ O[dbnd]C hydrogen bonds. For all of the “acetamide family” of the compounds, similar changes in the Raman spectra were observed upon cooling of the samples: emergence of new Amide I(−) and Amide I(+) bands, which are red and blue shifted, respectively, from the conventional Amide-I band by around of 5–10 cm− 1. Corresponding changes in the same temperature range were observed for the N[sbnd]H out-of-plane bending (Amide V) and N[sbnd]H stretching vibrations of the N[sbnd]H ⋯ O[dbnd]C hydrogen bond. All of the spectral changes observed upon cooling of the samples can be presumed to result from a delocalization of the Amide-I and N[sbnd]H modes and appearance of dynamical (Davydov's) splitting at low temperature.

KW - Dynamical splitting

KW - Hydrogen bonds

KW - Molecular crystals

KW - Raman spectra

KW - Secondary amides

KW - SOLITONS

KW - NEUTRON-DIFFRACTION

KW - VARIABLE-TEMPERATURE

KW - PARACETAMOL P-HYDROXYACETANILIDE

KW - ACETANILIDE

UR - http://www.scopus.com/inward/record.url?scp=85013746628&partnerID=8YFLogxK

U2 - 10.1016/j.saa.2017.02.046

DO - 10.1016/j.saa.2017.02.046

M3 - Article

C2 - 28249236

AN - SCOPUS:85013746628

VL - 179

SP - 216

EP - 220

JO - Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy

JF - Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy

SN - 1386-1425

ER -