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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
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Conformational preferences for 3-piperideines: an Ab initio and molecular mechanics study

A M Belostotskii1, M Shokhen, H E Gottlieb

  • 1Chemistry Department, Bar-Ilan University, Ramat-Gan, Israel. belostot@mail.biu.ac.il

Chemistry (Weinheim an Der Bergstrasse, Germany)
|January 5, 2002
PubMed

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The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal tetrahedral value,...
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At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
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Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).
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