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Conformations
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
The steric and electronic interactions in these molecules are relieved by pseudorotation, and the lowest average conformation is known as the so-called “butterfly” conformation for cyclobutane, the “envelope” conformation for cyclopentane, and the “chair” conformation for cyclohexane. Clearly, due to the pseudorotation, cyclic alkanes do not exist in a planar conformation because that conformation will be very high in torsion strain and in Baeyer stain. An exception is cyclopropane because pseudorotation is difficult. In the conformations shown, the torsion strain and any Baeyer strain has been relieved. Indeed, the H—C—C bond of cyclohexane resembles the gauche conformation of butane.
Synthesis, spectroscopic profiling, biological evaluation, DFT, molecular docking and mathematical studies of 3,5-diethyl-2r,6c-diphenylpiperidin-4-one picrate
Published in Molecular Physics, 2023
S. Bharanidharan, S. Savithiri, G. Rajarajan, P. Sugumar, A. Nelson
Figure 6 depicts the optimised molecular structure of 3,5-DEDPPP. The comparative optimised structural parameters, such as bond lengths, bond angles and dihedral angles values are displayed in Table S1 (Supporting Information) using the B3LYP/6-311++G(d,p) basis set. The bond distances between C–C, C–O, C–N, N–H, C–H and N-O are computed at same level of theory. Additionally, the bond angles and dihedral angles values are calculated at the same theoretical level and also compared with related XRD data [36]. The comparison of bond lengths of C53-C54 [1.4526/DFT and 1.437/XRD Å], C54-C55 [1.4529/DFT and 1.439/XRD Å], C52=C53 [1.3952/DFT and 1.374/XRD Å], C50=C55 [1.3944/DFT and 1.372/XRD Å] and C54=O67 [1.2511/DFT and 1.243/XRD Å] with normal bond lengths of C–C, C=C and C=O, it is found that C53-C54, C54-C55 (1.4 Å) have single bond character and C52=C53, C50=C55 (1.39 Å) have double bond character. The C=O (1.21 Å) also carries double bond character. This clearly indicates that the compound possesses more quinonoid character than benzenoid character. Due to an equatorial orientation of all the substituents, the torsional angle of C4-C5-C2-C21 is 178.8458°/DFT and 179.35°/XRD and C4-C5-C1-C10 is 177.5286°/DFT and 177.27°/XRD, respectively. The crucial features for an optimised molecular structure adopt a normal chair conformation.
Synthesis, spectral characterisations of 3t-pentyl-2r,6c-diarylpiperidin-4-one oxime picrates: DFT studies and potent anti-microbial agents
Published in Molecular Physics, 2022
S. Savithiri, G. Rajarajan, S. Bharanidharan, M. Arockia doss
The field of medicinal chemistry greatly benefits from the use of piperidine heterocycles. The relative chemical shift order of equatorial and axial protons in the normal chair conformation of cyclohexane and its derivatives (δeq > δax) are considered as caused by the magnetic anisotropic effect of the C–C single bonds. The influence of substituents on the chemical shifts of protons attached to the adjacent carbons has been studied in detail [1–3]. The picrate derivatives are of some 3-methyl-2,6-diarylpiperidin-4-ones and 3,5-dimethyl-2,6-diarylpiperidin-4-ones. In contrast to the value observed in the parent piperidin-4-ones, the chemical shift difference between the equatorial and axial methylene protons at (C-5) for these derivatives [Δ = δeq − δax] is highly negative. This was explained by the syn 1,3-diaxial interaction between the axial N–H bond and axial proton at C-5. It was carefully examined how protonation affected chemical changes. The picrate anion affects the chemical shift of the heterocyclic ring protons [4]. Furthermore, they synthesised 3t-alkyl-2r,6c-diphenyl-4-oxopiperidinium nitrate. In the solid state and solution, the piperidine ring in 3t-isopropyl-2r,6c-diphenyl-4-oxo piperidinium nitrate adopts chair conformation with the equatorial orientation of the phenyl and isopropyl groups [5].