J. L. Núñez

Accurate scaling of the vibrational spectra of aniline and several derivatives

The structure of aniline was studied by quantum chemical methods. Complete geometry optimization of the minimum energy structure and of the transition states for internal rotation and inversion of the amino group was carried out using several levels. The performance of the different methods in calculating and describing the vibrational wavenumbers of aniline was determined. The normal modes were characterized by the magnitude and direction of the displacement vectors. Three procedures were used to obtain the scaled wavenumbers, two of them new, using specific scale factors and scaling equations from benzene molecule. The errors obtained were compared with those calculated through other standard procedures. A reassignment of several bands was made. A comparison of the cost/effective method and procedure of scaling was carried out. Specific scale factors and scale equations were determined for the amino group to be used in large aromatic amines.

Structure and spectral characteristics of o-aminobenzoic acid by AM1

Abstract The geometry of the o -aminobenzoic acid (anthranilic acid) molecule in two stable conformations was obtained with the AM1 semiempirical method. All geometric parameters, torsional angles included, were fully optimized by means of a quantum mechanic program package. The frequency and intensity of the vibrational bands were calculated and related to the IR and Raman spectra through several scaling coefficients used to improve the theoretical spectra. The total atomic charges, electron density, dipole moment and several thermodynamic and structural parameters were also computed.

Spectroscopy of p-Methoxybenzoic Acid: An AM1 and ab Initio Study

The vibrational spectra of p-methoxybenzoic acid (anisic acid) were calculated and compared with the experimental spectra. All measured bands in the IR and Raman spectra were interpreted in terms of calculated vibrations from the AM1 and 4–21G* methods, and their frequencies were correlated. Several scale coefficients were used to improve the theoretical spectra. The optimum geometric parameters were also computed with the AM1 semiempirical method and with the 4–21G* ab initio procedure.

Meta - Aminobenzoic Acid: Structures and Spectral Characteristics

Abstract Two conformations of minimum energy (I-syn and I-anti) were found in meta-aminobenzoic acid by the AMI semiempirical method. All the geometric parameters were optimized and compared with published data obtained by means of X-ray diffraction. The dipolar form of meta-aminobenzoic acid was also optimized by AM1. The vibrational spectra were computed in all cases. Several scale coefficients were used to improve the theoretical spectra. The total atomic charges, the electronic density and several thermodynamics parameters were also calculated.

Infrared Study of Phenothiazine and N-Methyl Phenothiazine

Phenothiazine (PhT) (fig. 1) and N-methyl phenothiazine (N-MePhT) are of special interest for their properties as photosensitizer, possible mutagen, and toxicity. Phenothiazine is employed in the preparation of carbazoles, piperazines [1] and charge-transfer semiconducting complexes [2]. Readily absorbed through the skin, is accumulated in liver and blood.

Quantum Chemical Predictions of the NMR Spectrum of Phenothiazine and N-Methyl Phenothiazine

Phenothiazine (PhT) (fig. 1) and N-methyl phenothiazine (Af-MePhT) are of special interest for their properties as photosensitizer, possible mutagen, and toxicity. Phenothiazine is employed in the preparation of carbazoles, piperazines [1] and charge-transfer semiconducting complexes [2]. NMR studies could be a powerfull tool of differentiation between the different phenothiazines and also provide structural information.

A Study of Para-Aminobenzoic Acid: Structure, Frequencies, Torsion and Inversion Barriers of the Amino Group

The structure of p-aminobenzoic acid was optimized by ab initio and semiempirical quantum chemical methods. The calculated vibrational spectra were compared with the infrared and Raman data. The full ring vibrational modes were identified and characterized. The torsion and inversion barriers of the amino group were calculated.

Neutral and Dipolar forms of Meta-Aminobenzoic Acid

The neutral and dipolar forms of m-aminobenzoic acid were studied by ab initio and semi-empirical quantum mechanic methods. The full infrared spectrum was interpreted.

A Spectroscopic Study of Several β-Lactams by FT-IR and Theoretical Methods

The chemical and biological activity of β-lactam derivatives, has reached a great role in clinic uses, as semi-synthetic antibiotics. Theoretical studies of β-lactam antibiotics, from the point of view of their geometric structure and conformations have been reported [1], [2].

Characterization of the β-Lactam Ring Fundamental Vibrations by Ab Initio and FT-IR Methods

The β-lactam molecules of 2-azetidinone and 3-methyl-2-azetidinone were studied by ab initio methods. The calculated vibrational spectra of both molecules were compared with the experimental frequencies of 2-azetidinone and 3-methyl-4-benzoyl-4-phenyl-2-azetidinone. The vibrational frequencies and intensities of the normal modes from the four-member ring, were identified. Several frequencies were proposed as analytically useful to characterize the β-lactam ring. The relative utility of these ring frequencies was discussed.