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I. Rearrangement of Cyclopropyldiphenylmethyllithium and 4,4-Diphenyl-3-Buten-1-Yllithium. II. Deuterium Isotopic Perturbation of the Cyclopropylmethyl-Cyclobutyl Carbocation

Citation

Brittain, William Joseph (1982) I. Rearrangement of Cyclopropyldiphenylmethyllithium and 4,4-Diphenyl-3-Buten-1-Yllithium. II. Deuterium Isotopic Perturbation of the Cyclopropylmethyl-Cyclobutyl Carbocation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/1c58-f235. https://resolver.caltech.edu/CaltechTHESIS:05102018-165616024

Abstract

PART I

Cyclopropyldiphenylrnethyllithium was prepared directly from cyclopropyldiphenylmethane by trimethylsilylmethyllithium metalation or indirectly by transmetalation of cyclopropyldiphenylmethylpotassium. The organolithium is stable in tetrahydrofuran, dimethyl ether, or 2-methyltetrahydrofuran and exists predominately as loose ion pairs. In diethyl ether or isopropyl methyl ether, cyclopropyldiphenylmethyllithium isomerizes to 4,4-diphenyl-3-buten-1-yllithium; a process that can be reversed by addition of tetrahydrofuran. 4,4-Diphenyl-3-buten-1-yllithium is unstable in most solvents; in cyclopentane, β-elimination of lithium hydride and ortho-cyclisation were major reaction pathways. The solvent dependence of the organolithium rearrangement can be adequately explained by three principle equilibria; the rearrangement occurring in contact ion pairs.

PART II

Ionization of (2E,2Z,3Z-d3-cyclopropyl)methanol. 9, in SbF5-SO2ClF-SO2F2 afforded primarily one stereoisomer (endo-C4H4D3+) of the trideuterated cyclopropylmethyl-cyclobutyl carbocation. Ionization of (2,2-d2-cyclopropyl)-1-d-methanol, 10, in SbF5-SO2ClF-SO2F2 produces a 1:1 mixture of endo- and exo-C4H4D3+. The low-temperature 1H, 2H, and 13C NMR spectra of both C4H4D3+ stereoisomers are reported. The methine resonance (13CH) of exo-C4H4D3+ is shifted 0.4 ppm downfield from unlabeled cation, C4H7+, while the endo-C4H4D3+ resonance is coincident with the corresponding carbon in C4H7+. This can be taken as evidence for the deuterium isotopic perturbation of the equilibrium between bicyclobutonium, 2, and bisected cyclopropylmethyl, 4, structural isomers. The deuterium perturbation of equilibria involving structurally similar, nondegenerate isomers is a larger effect and induces dramatic changes in the methylene carbon resonances. The 13C resonance corresponding to the mondeuterated carbon (13CH2) is shifted in opposite directions relative to C4H7+ in endo- and exo-C4H4D3+. Endo-C4H4D3+ slowly isomerizes to exo-C4H4D3+; a lower limit for the rotation barrier in C4H4D3+ is 14 ± 1 kcal/mol. The endo-hydrogens in endo-C4H4D3+ were assigned to the high-field methylene resonance in the 1H spectrum of this ion in contrast to previous assignments by other workers. The results of this NMR study of C4H4D3+ carbocations are consistent with two rapidly equilibrating structures, 2 and 4, of C4H4D3+ under stable-ion conditions.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Chemistry
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Unknown, Unknown
Thesis Committee:
  • Dervan, Peter B. (chair)
  • Roberts, John D.
  • Grubbs, Robert H.
  • Dougherty, Dennis A.
Defense Date:3 May 1982
Funders:
Funding AgencyGrant Number
CaltechUNSPECIFIED
Record Number:CaltechTHESIS:05102018-165616024
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:05102018-165616024
DOI:10.7907/1c58-f235
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10875
Collection:CaltechTHESIS
Deposited By: Melissa Ray
Deposited On:14 May 2018 16:06
Last Modified:16 Apr 2021 22:14

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