I. Structural Analysis Using 15N NMR Spectroscopy II. An Investigation of the Interaction of Grignard Reagents with Mesityl Ketones

Citation

Abe, Amy (1979) I. Structural Analysis Using 15N NMR Spectroscopy II. An Investigation of the Interaction of Grignard Reagents with Mesityl Ketones. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/m0ya-bx45. https://resolver.caltech.edu/CaltechTHESIS:03012018-155039057

Abstract

PART I. Structural Analysis Using ¹⁵N NMR Spectroscopy

The proton-coupled, natural-abundance ¹⁵N NMR spectra of three series of compounds were examined with emphasis on obtaining conformational, structural and configurational data.

Amino acids and peptides. Chemical shifts of aliphatic amino acids and glycyl dipeptides followed typical α, β, and γ-substituent effects. Vicinal ¹⁵N_α, H_β coupling constants were obtained for seven amino acids and Gly-X dipeptides which possess ~ither a single or three equivalent β-protons. Average vicinal couplings were obtained for amino acids with diastereotopic β-protons. Conformational preferences for the rotamers about the C_α - C_β bond of threonine and allothreonine were found by extending the traditional Pachler analysis to allow for interaction among substituents through treating both population and torsion angle as variables. Hydrogen-bond formation between the hydroxyl and the carboxylate was favored over that between the hydroxyl and nitrogen for both amino acids.

Biotin. The proton on the N1' nitrogen of biotin exchanges more readily with solvent than that on the sterically-hindered N3' nitrogen. The order of exchange was established through correlation of the nitrogen NMR resonances with the ureido proton resonances by variable single-frequency decoupling of the ureido protons and through assignment of the proton spectrum by homonuclear-decoupling experiments. Assignment of the nitrogen resonances in biotin (N1' = 285.6 ppm and N3' = 294.7 ppm) and desthiobiotin (N1' = 279.3 ppm and N3' = 285.0 ppm) was achieved with the aid of single-frequency, proton-decoupled nitrogen resonances with partial NOE.

Oximes. The large difference between two-bond ¹⁵N, H_α coupling constants for the E- and Z-isomers of the oximes allows the configurations of aldoximes to be assigned from geminal couplings obtained from the ¹⁵N NMR spectra and also the configuration of O-alkylaldoximes from nitrogen spectra in which the protons on the alkyl group are selectively decoupled.

PART II. An Investigation of the Interaction of Grignard Reagents with Mesityl Ketones

The reaction of acetomesitylene with benzyl Grignard reagent was reinvestigated because of uncertainty in the mechanism and site of addition of the benzyl moiety. The addition product was identified as mesitylmethylbenzylcarbinol as is consistent with a "normal" addition to the ketone proceeding through an initial ketone-Grignard reagent complex.

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