Iss 2 Citation: Zeyede Aregahegn. Structural Study on Propylamide by FT-IR Spectrometry Using Chemometrics Applications (original) (raw)
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The tautomeric equilibrium of several amides and related compounds is studied experimentally via mass spectrometry techniques. Experimental findings are complemented with theoretical calculations in order to rationalise mass spectra results of some amides, thioamides, ureas and thioureas. Some further possible studies are pointed out in order to complement present findings. Both mass spectra and theoretical results indicate that tautomerism involves neutral species rather than the ionic analogues. Besides, thio-derivatives have a relatively higher tendency to occur as imidols. ᭧
Journal of Molecular Structure, 1999
Ab initio molecular orbital calculations at HF/4-31G level and infrared spectroscopic data for the frequencies are applied to analyse the grouping in a series model aromatic secondary amides: formanilide; acetanilide; o-methylacetanilide; 2,6-dimethylformanilide, 2,6-dimethylacetanilide; N-benzylacetamide and N-benzylformamide. The theoretical and experimental data obtained show that the conformational state of the molecules studied is determined by the fine balance of several intramolecular factors: resonance effect between the amide group and the aromatic ring, steric interaction between various substituents around the -NH-CO-grouping in the aromatic ring, conjugation between the carbonyl bond and the nitrogen lone pair as well as direct field influences inside the amide group. ᭧
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2023
The structural and vibrational properties of naproxen, an inhibitor of cyclooxygenase (COX) enzyme, were investigated by molecular modeling and experimental IR and Raman spectroscopic techniques. Possible conformers of the molecule were searched via a molecular dynamics simulation carried out with MM2 force field. The total energies, equilibrium geometries, force fields, IR and Raman spectral data of the found stable conformers were determined by means of geometry optimization and harmonic frequency calculations carried out using the B3LYP method and Pople-style basis sets of different size. The stability order obtained for the lowest-energy conformers was confirmed by high-accuracy thermochemistry calculations performed with G3MP2B3 composite method. Some electronic structure parameters of naproxen and the anharmonicity characters of its vibrational modes were determined by means of natural population analysis (NPA) and anharmonic frequency calculations at B3LYP/6-31++G(d,p) and B3LYP/6-311++G(d,p) levels of theory. A part of these calculations carried out for free naproxen molecule were repeated also for its energetically most favored dimer forms. Two different scaling procedures ((1) "SQM-FF methodology" and (2) "Dual scale factors") were independently applied to the obtained harmonic vibrational spectral data to fit them to the corresponding experimental data. In the light of the obtained calculation results, which confirm the remarkable effects of conformation and intermolecular hydrogen bonding on the structural and vibrational spectral data, in particular, on those associated with the functional groups in the propanoic acid chain, a reliable assignment of the fundamental bands observed in the experimental IR and Raman spectra of the molecule was achieved.
The Journal of Physical Chemistry A, 2007
The amide bond may be considered as one of the most important chemical building blocks, playing an important role not only in living organisms but in organic chemistry as well. The exact description and precise quantification of the amide bond strength is difficult, requiring a particular type of theoretical investigation. The present paper suggests a novel, yet simple, method toward quantifying amide bond strength on a linear scale, defined as the "amidity scale". This is achieved using the computed enthalpy of hydrogenation (∆H H2 ) of the compound examined. In the present conceptual work, the ∆H H2 value for dimethylacetamide is used to define perfect amidic character (amidity ) +100%), while azaadamantane-2-on represents complete absence of amidic character (amidity ) 0%). The component ∆H H2 values were computed at differing levels of theory, providing a computational and quasi-"method-independent" measure of amidity. A total of 29 well-known amides were examined to demonstrate the "scoring" accuracy of this methodology. For the compounds examined, a correlation has been made between the computed amidity percentage and their common COSNAR resonance energy values, proton affinities, and reactivity in a nucleophilic addition reaction. Selected chemical reactions were also studied. It has been shown that the change of the amidity value, during acyl transfer reactions, represents a thermodynamic driving force for the reaction.
Recent advances in the chemistry of stable simple enols
Pure and Applied Chemistry, 1997
Two new aspects of the chemistry of simple bulky-aryl substituted enols are described. (i) The reactions of amines such as Me2NH, morpholine piperidine, or pyrrolidine with ditipyl ketene (tipyl = Tip = 2,4,6-tri-isopropyl-phenyl) generate the enol of the amide Tip2C=C(OH)NR1R2 which is observed and characterized by NMR spectra. The addition reaction is reversible. Further tautomerization of the enol to the stable conformer of the amide is relatively slow and involves an additional NMR observable intermediate which is presumably the kinetically controlled unstable conformer of the amide. (ii) Di-and tri-bulky arylvinyl alcohols and their derivatives such as the ethers or acetates are chiral, having a propeller conformation. The enantiomerizations of triarylethenols usually proceed by a three ring flip, and the rotational barriers are mostly too low for resolution of stereoisomers. In the Mes2C=C(OH)(2-X-9-anthryl) system where X = F, OMe, the a-ring lacks a C2 symmetry and enantiomerization barriers in which this ring passes through the molecular plane are higher. Resolution on an optically active column is achieved when X = F, but fast enantiomerization then takes place. This is probably due to an E-Z enol interconversion which was observed in other systems.
The Journal of Chemical Physics, 2002
A combination of methods, including laser-induced fluorescence excitation, fluorescence-dip infrared ͑FDIR͒ spectroscopy, and UV-UV hole-burning spectroscopy, have been used to study the infrared and ultraviolet spectra of single conformations of two methyl-capped dipeptides: N-acetyl tryptophan amide ͑NATA͒ and N-acetyl tryptophan methyl amide ͑NATMA͒. Density functional theory calculations predict that all low-energy conformers of NATA and NATMA belong to one of two conformational families: C5, with its extended dipeptide backbone, or C7 eq , in which the dipeptide backbone forms a seven-membered ring joined by a H bond between the -amide NH and the -amide carbonyl groups. In NATA ͑NATMA͒, the LIF spectrum has contributions from two ͑three͒ conformers. FDIR spectroscopy has been used to record infrared spectra of the individual conformers over the 2800-3600 cm Ϫ1 region, free from interference from one another. The NH stretch region provides unequivocal evidence that one of the conformers of NATA is C5, while the other is C7 eq . Similarly, in NATMA, there are two C5 conformers, and one C7 eq structure. Several pieces of evidence are used to assign spectra to particular C5 and C7 eq conformers. NATA͑A͒ and NATMA͑B͒ are both assigned as C5͑AP͒ structures, NATA͑B͒ and NATMA͑C͒ are assigned as C7 eq ͑⌽P͒, and NATMA͑A͒ is assigned as C5͑A⌽͒. In both molecules, the C5 structures have sharp vibronic spectra, while the C7 eq conformers are characterized by a dense, highly congested spectrum involving long progressions that extend several hundred wave numbers to the red of the C5 S 1 -S 0 origins. N-acetyl tryptophan ethyl ester ͑NATE͒, which can only form C5 conformers, shows only sharp transitions in its LIF spectrum due to four C5 conformers, with no evidence for the broad absorption due to C7 eq . This provides direct experimental evidence for the importance of the peptide backbone conformation in controlling the spectroscopic and photophysical properties of tryptophan.
Journal of Molecular Structure, 2011
The analysis of the IR carbonyl bands of some 3-(4′-substituted phenylsulfanyl)-1-methyl-2-piperidones 1-6 bearing substituents: NO 2 (compound 1), Br (compound 2), Cl (compound 3), H (compound 4) Me (compound 5) and OMe (compound 6) supported by B3LYP/6-31+G(d,p) and PCM calculations along with NBO analysis (for compound 4) and X-ray diffraction (for 2) indicated the existence of two stable conformations, i.e., axial (ax) and equatorial (eq), the former corresponding to the most stable and the least polar one in the gas phase calculations. The sum of the energy contributions of the orbital interactions (NBO analysis) and the electrostatic interactions correlate well with the populations and the ν CO frequencies of the ax and eq conformers found in the gas phase. Unusually, in solution of the non-polar solvents n-C 6 H 14 and CCl 4 , the more intense higher IR carbonyl frequency can be ascribed to the ax conformer, while the less intense lower IR doublet component to the eq one. The same ν CO frequency trend also holds in polar solvents, that is ν CO (eq) < ν CO (ax) . However, a reversal of the ax/eq intensity ratio occurs going from non-polar to polar solvents, with the ax conformer component that
Journal of Molecular Structure, 2009
The analysis of the IR carbonyl bands of some 3-(4′-substituted phenylsulfanyl)-1-methyl-2-piperidones 1-6 bearing substituents: NO 2 (compound 1), Br (compound 2), Cl (compound 3), H (compound 4) Me (compound 5) and OMe (compound 6) supported by B3LYP/6-31+G(d,p) and PCM calculations along with NBO analysis (for compound 4) and X-ray diffraction (for 2) indicated the existence of two stable conformations, i.e., axial (ax) and equatorial (eq), the former corresponding to the most stable and the least polar one in the gas phase calculations. The sum of the energy contributions of the orbital interactions (NBO analysis) and the electrostatic interactions correlate well with the populations and the ν CO frequencies of the ax and eq conformers found in the gas phase. Unusually, in solution of the non-polar solvents n-C 6 H 14 and CCl 4 , the more intense higher IR carbonyl frequency can be ascribed to the ax conformer, while the less intense lower IR doublet component to the eq one. The same ν CO frequency trend also holds in polar solvents, that is ν CO (eq) < ν CO (ax) . However, a reversal of the ax/eq intensity ratio occurs going from non-polar to polar solvents, with the ax conformer component that