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Abstract
Part I. The stereochemistry of hydride reduction of the acyclic ketone 3-phenyl-2-butanone and the cyclic analogue 2-phenyl cyclohexanone was investigated using a variety of aluminum, boron, and silicone hydrides. It was observed that in both the acyclic and cyclic systems, temperature, metal cation associated with the hydride, solvent, and groups alpha to the ketone group fail to be a dominant factor in directing stereochemistry during reduction. The size of the hydride was however found to be of greatest importance in the cyclic systems while of much lesser significance in the acyclic system. Isotope effects and product ratio studies suggest the possibility of non chair even distorted boat conformations in the transition state to adequately explain rates of reduction, isotope effects, and steric effects leading to observed products. A new carbon-13 method was developed to accurately determine product ratios which used the paramagnetic metal complex Cr(AcAc)(,3) as a relaxation agent.
Part II. The carbon-13 proton coupled spectrum of a wide variety of ortho-substituted aromatics which in principal were capable of intramolecular hydrogen bonding were studied. It was found that a large majority of the 1,2 substituted aromatics with the amino,phenol, and amide groups as proton donors, bonded in tramolecularly with accepting groups such as ketone and ester carbonyls, nitro, methoxy, and others to the extent that on the NMR time scale exchange rates were slow enough so as to be able to see the three bond couplings into the aromatic ring. The value of the couple is in the region of 5-7 Hz for an anti geometry between the C(,3) and hydrogen bonded proton and about 2-3 Hz for the syn arrangement. These values were found to be both ring size independent (size of the ring in the hydrogen bonding array) and the coupling constant relatively insensitive to dihedral angle.
Part III. The conformational analysis on a series of acyclic vicinal acyclic nitro-alcohols were performed. The systems employed were designed to test both the preference for hydrogen bonding as a controlling factor in conformation as well as electronegative effects. Found was that the nitro group contrary to its behavior in aromatic systems is a poor hydrogen bond acceptor and that the stereochemistry for both erythro and threo isomers are dominated by steric interactions. It is found that where there were vicinal dialkyl or alkyl-aryl groups the trans arrangement between these groups is preferred. The effect of the trihalo group -CX(,3) is one of varying steric size (CF(,3) (--->) CBr(,3)) rather than electronic effects. In one case containing the -CCl(,3) group preferred conformations suggest some type of attractive steric or electronic effects between the trihalo methyl and nitro groups.
