Quantum chemical study of several monocyclic complex β‐lactam C‐3, C‐4, and N‐derivatives, and β‐ring model molecules

Abstract

ABSTRACT:A quantum chemical study of several complex monocyclic 4-benzoyl-4-phenyl-␤-lactam derivatives was carried out using cyclobutane, azetidine, 2-azetidinone, 1-methyl-2-azetidinone, and 3-methyl-2-azetidinone as model compounds. The optimum geometry was obtained for the different conformations. The planarity of the ring was discussed in terms of the influence of the substituents on the amide resonance. To better analyze the amide resonance and the activity of the ␤-lactam ring, a vibrational study was also carried out. To examine the influence of solvent polarity on the carbonyl bands, the Fourier transform-infrared (FT-IR) spectra of the ␤-lactam monocyclic derivatives were recorded in CCl 4 , C 6 H 6 , and CHCl 3 solutions. The normal vibrations of the ␤-lactam ring in the model compounds were characterized and used in the analysis of the ␤-ring of more complex derivatives.

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants. Part 8—Monocycloalkanes

“…Our present B3LYP/6-311G ŁŁ value of  D 24.3°is in good agreement with the corresponding B3LYP/6-311CCG (3df,pd) result of 25.3°reported by Palafox et al 51 It is interesting that semiempirical methods fail to establish the cyclobutane ring puckering, giving a planar form which is actually a saddle point between two degenerate bent equilibrium structures, as follows from the harmonic vibrational frequencies analysis. 50 …”

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants. Part 10—Carbocages

“…ased on x-ray, 51 electron diffraction, 52,53 microwave 54 and other spectroscopic data 55 and in conformity with DFT 1,56,57 calculations. In this regard, cubane provides an interesting simulation of hypothetical planar cyclobutane, which is actually a saddle point between two degenerate bent equilibrium structures, as follows from the harmonic vibrational frequency analysis.…”

High resolution Fourier transform infrared spectra and analysis of the ν14, ν15 and ν16 bands of azetidine

“…The DFT (B3LYP (6-31G ** )) calculations of Thompson et al [20] show a similar level of agreement with reported values of 748.7, 657.1 and 212 cm À1 , respectively. The estimate of the ring puckering frequency (206 cm À1 ) appears to improve with the use of a larger basis set as shown by the B3LYP (6-311 ++ G(2d,p)) calculations of Palafox et al [19], but the agreement for the m 14 mode actually worsens with the expanded basis (and the authors have not reported the m 15 frequency). Collectively, these results highlight the importance of complementary experimental and theoretical investigations of the fundamental structural and dynamical properties of small molecules.…”

“…In addition to the extensive investigation of the ring puckering mode of azetidine, the higher frequency modes have been calculated via ab initio methods and the infrared spectrum has been measured in the gas phase [16,18], in solution [18,19] and in a solid argon matrix [20]. Dutler et al [18] recorded the gas phase infrared spectrum from 400 to 3400 cm À1 at a resolution of 0.12 cm À1 and 0022-2852/$ -see front matter Ó 2010 Elsevier Inc. All rights reserved.…”