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Eclipsed conformations for simple saturated bonds

Ijeh, Anthony Ibhakhomon; (1996) Eclipsed conformations for simple saturated bonds. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

This thesis is primarily concerned with demonstrating bond eclipsing and its consequences in simple saturated compounds using dynamic nuclear magnetic resonance spectroscopy and molecular mechanics calculations. I report the three-fold equilibria in cyclic aza/poly-aza compounds and two-fold rotational equilibria in trialkylamines. The dynamic stereochemistry of a range of N-neopentyl piperidines with eclipsed N-CH2But bonds is compared with that of the corresponding N-ethylpiperidines, with gauche N-CH2Me bonds. The relative importance of ring inversion, exocyclic bond rotation and nitrogen inversion is elucidated, barriers of these processes are discussed and reported with the help of Molecular Mechanics calculations. The effect of including cis equatorial methyl groups at the 2 and 6 positions of the piperidine ring was investigated, and examples of bonds which can adopt either eclipsed or staggered conformation are demonstrated. Dynamic studies are reported for poly-aza compounds i.e. N,N'-dineopentyl-hexahydropyrimidine and Tris(neopentyl)-1,3,5-triazane which has been shown by X-ray diffraction study to have one axial and two equatorial neopentyl groups with eclipsing in both axial and equatorial exocyclic N-CH2 bonds. A dynamic NMR study of a range of acyclic N,N-dialkylneopentylamines supported by Molecular Mechanics calculations, showed that eclipsed conformations are encountered for N-CH2But bond which has a high one-fold rotational barrier, with more branched alkyl groups it was shown that the bond adopts an intermediate between staggered and eclipsed. Lastly a detailed dynamic NMR investigation with Molecular Mechanics calculations has been carried out on the protonated derivatives of these cyclic and trialkylamines with the information obtained from vicinal H-N+-C-H coupling and one bond carbon-proton coupling, conformation of bonds were established.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Eclipsed conformations for simple saturated bonds
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Pure sciences; Bond eclipsing
URI: https://discovery.ucl.ac.uk/id/eprint/10102829
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