Theoretical quantum chemical study of benzoic acid: Geometrical parameters and vibrational wavenumbers

Abstract

ABSTRACT:The structure of benzoic acid as monomer was studied by semiempirical, ab initio, and density functional methods using several basis sets. The performance of these methods in calculating and describing the vibrational frequencies of benzoic acid and several derivatives was determined. The cyclic dimer form of benzoic acid was also reproduced. Two new procedures of scaling the frequencies were presented. For the ring modes, specific scale equations and scale factors were used from benzene molecule. For the carboxylic group, scaling equations and specific scale factors at different levels were also determined to be used in benzoic acid derivatives. A reassignment of several bands was done. A comparison of the cost/effective method and procedure of scaling was carried out. A significant reduction of the error in the predicted frequencies was obtained over the one-factor standard scaling procedure.

Vibrational Study and Force Field of the Citric Acid Dimer Based on the SQM Methodology

“…In this case, some coordinates are slightly different from those used in the previous study [15]. The six inter-monomer coordinates for this dimer are similar to those defined by other authors for other dimeric acids [33][34][35][36], which can be seen in Supplementary Table S2. Following the SQMFF procedure [37,38] Table S3) by using both basis sets.…”

“…The intermonomer vibrational modes of the dimer usually appear in the 270-10 cm −1 region [33][34][35][36]40] and they are related to restricted translations or rotations of one molecule against the other (see Supplementary Table S2). Here, the six intermonomer modes appear strongly coupled with other modes and they are observed in the Raman spectrum with the exception of the γ a (OH-O) mode that was predicted by calculations with a higher contribution PED (42%) at 827 cm −1 ; for this reason, it is assigned to the very weak Raman band at 842 cm −1 .…”

“…The recorded infrared spectra for the compound in the solid phase can be seen in Figure 2. The assignment of the experimental bands to the 120 expected normal vibration modes was made on the basis of the Potential Energy Distribution (PED) in terms of symmetry coordinates by using the B3LYP/6-31G * data and taking into account the previous assignment for the monomer [15] and for related molecules [33][34][35][36]40]. Table 1 shows the observed frequencies and the assignment of the vibrational normal modes while the PED based on the 6-31G * basis set is shown in Supplementary Table S5.…”

Anharmonic midinfrared vibrational spectra of benzoic acid monomer and dimer

“…Due to deficiencies of the quantum chemical calculations and/or due to the neglect of anharmonic effects, these frequencies are typically a few percent higher than the observed ones. However, using empirical scaling factors, satisfactory quantitative agreement with experimental vibrational spectra in the mid-IR regime can be achieved in many cases [15]. Nonetheless, pronounced discrepancies are occasionally found, e. g., for vibrational modes where the contributing atoms are directly involved in a hydrogen bond.…”

Substituent Effects on the Low‐Frequency Vibrational Modes of Benzoic Acid and Related Compounds

“…A lot of experimental and theoretical investigations have been conducted on BA dimer. [12][13][14] Florio et al 11,12 have used theoretical modeling to study the infrared spectrum of BA dimer in its ground and first excited singlet states. Nandi and coworkers 13 studied hydrogen bond-induced vibronic mode mixing in BA dimer with laser-induced dispersed fluorescence spectroscopy.…”