Overtones of νC≡N Vibration as a Probe of Structure of Liquid CH₃CN, CD₃CN, and CCl₃CN: Combined Infrared, Near-Infrared, and Raman Spectroscopic Studies with Anharmonic Density Functional Theory Calculations

Abstract

The νCN band (νCN) is a sensitive probe of the state of molecules with nitrile groups. Hence, physicochemical properties of acetonitrile and its derivatives have been frequently investigated by means of vibrational (IR and Raman) spectroscopy. Near-infrared (NIR) spectroscopy combined with high-level quantum mechanical calculations offers deeper physical insight into the structure of liquid nitriles not available from the fundamental region. This results from unique information provided by the overtones of νCN. Here, we report an application of anharmonic vibrational calculations coupled with IR, NIR, and Raman spectroscopy for investigation of the structure of CH 3 CN, CD 3 CN, and CCl 3 CN in the liquid phase. The computational part was based on generalized vibrational second-order perturbation theory (GVPT2) applied on the density function theory (B3LYP, M06-2X, and B2PLYP) level to monomers as well as linear and cyclic dimers. The obtained data were refined by counterpoise-corrected MP2 calculations to mimic the aggregation in the liquid state. Our results evidence that the intensity variations between the fundamental, first and second overtones of the νCN band depend on the symmetry of aggregated species. The symmetry of the cyclic dimers in liquid nitriles was elucidated from the relative intensity of the 2νCN band. This work advances our understanding of the vibrational spectra of acetonitrile and its derivatives by providing detailed band assignment of IR, NIR, and Raman spectra. For the first time, we reported the position of the first and second overtones of the nitrile group.

Spectra–Structure Correlations in Isotopomers of Ethanol (CX3CX2OX; X = H, D): Combined Near-Infrared and Anharmonic Computational Study

“…However, the studies using a vibrational self-consistent field (VSCF) approach [13,14] and its refined variants—e.g., PT2-VSCF—are more common [15,16,17]. Recently, a number of theoretical reconstructions of NIR spectra by means of efficient vibrational second-order perturbation (VPT2) method have been reported [18]; e.g., carboxylic acids [19], fatty acids [20,21,22], aminoacids [23], nucleobases [24], nitriles [25], azines [26], phenols [27,28], and alcohols [29,30]. Considerable efforts have been undertaken in order to develop anharmonic approaches applicable to even larger molecular systems [31,32,33,34].…”

Simulated NIR spectra as sensitive markers of the structure and interactions in nucleobases

“…Highly accurate simulations of small- to medium-size molecules in solutions opened the way to exploration of more complex systems 42–44 . Quantum chemical calculations have been applied in studies of NIR spectra of basic molecules like alcohols 45 , phenols 46 , nitriles 47 , or carboxylic acids 48,49 . These studies cover also a series of important molecules including melamine 50 , thymol 51 , rosmarinic acid 52 , short- 53 , medium- 54 and long-chain fatty acids 55 .…”

“…These studies cover also a series of important molecules including melamine 50 , thymol 51 , rosmarinic acid 52 , short- 53 , medium- 54 and long-chain fatty acids 55 . These investigations provided interesting information on the effects of isotopic substitution 56,57 , rotational isomerism 23,45,48,57 , liquid structure 47 , conformational equilibria 23 , and hydrogen-bonding 47,49 .…”

Conformational Changes in the Structure of Dough and Bread Enriched with Pumpkin Seed Flour

“…Analyzing the reflection spectra of the dough after kneading, after 3.5 h of fermentation, and of bread (both control sample and sample with 20% pumpkin seed flour), the highest reflection was noted at wavelengths of 1460 nm, 1760 nm, 1930 nm, 2100 nm, 2270 nm, and 2350 nm ( Figure 6 ), with the extremum for all analyzed samples at 1460 nm, corresponding to the first overtone of valence vibrations of the OH group [ 36 ]. The functional groups of the first overtones, C-H and S-H, appear at 1760 nm [ 36 ]. Water is characterized by reflection at 1930 nm (OH deformation oscillations, the second overtone) [ 36 ].…”