Kenneth L. Servis

29Si NMR spectra of metal carbonyl silanes by the selective population transfer method

Abstract Utilization of the novel Selective Population Transfer (SPT) technique for the first NMR observation of 29Si nuclei directly bound to transition metals is reported. Four metal carbonyl trimethylsilanes ((CH3)3SiMn(CO)5, (CH3)3SiRe(CO)5, (CH3)3SiCo(CO)4, and (CH3)3SiFe(CO)2(C5H5)) have been studied and their chemical shifts and coupling constants obtained. These data are compared with existing 29Si NMR spectra of more conventional (CH3)3SiX compounds and 119Sn NMR spectra of homologous (CH3)3Snmetal complexes.

Silicon-29 NMR studies of polymethylhydrosiloxanes: Spin-lattice relaxation time (T1) measurements

Abstract 29 Si NMR spectra of polymethylhydrosiloxanes, Me 3 SiO[MeHSiO] n SiMe 3 from n = 3 to 8 and 35, have been determined. Both chemical shifts and spin-lattice relaxation times ( T 1 ) have been measured. The stereochemistry at the adjacent chiral MeHSiO unit influences the nearest neighbor 29 Si chemical shift. The effect of chain length and position of MeHSiO units on T 1 values for Me 3 SiO[MeHSiO] n SiMe 3 systems are discussed.

Proton Magnetic Resonance Studies of the Decomposition of 4-Hydroxycyclophosphamide, a Microsomal Metabolite of Cyclophosphamide

The proposed tautomeric equilibrium between the microsomal metabolite of cyclophosphamide, 4-hydroxycyclophosphamide, and the open chain aldophosphamide, and the subsequent facile β-elimination to generate acrolein and phosphoramide mustard have been confirmed by proton magnetic resonance studies. When 4-hydroxycyclophosphamide, initially maintained in CDC13 at −20°C, was allowed to equilibrate at 15°C, a singlet at 9.76 δ and a triplet at 2.88 δ appeared concomitantly which were assigned to the aldehydic proton and the protons α to the carbonyl of aldophosphamide, respectively. Further reaction led to the appearance of several NMR signals that indicated the irreversible formation of acrolein (multiplet at 9.55 δ) and phosphoramide mustard. Polymerization occurred approximately 2 hours after the initiation of the reaction. The kinetic data of the reaction sequence are discussed.

Conformational analysis of 2-butanone and 3-methyl-2-butanone using lanthanide shift reagents

Lanthanide-induced 13C and 1H NMR chemical shift ratios of 2-butanone and 3-methyl-2-butanone have been determined using the shift reagent Yb(fod)3. The induced shift data were analyzed to derive the conformational populations for these ketone-lanthanide chelate complexes. For 2-butanone, the cis conformation (methyl eclipsing the carbonyl) was found to be more stable than the gauche conformation (hydrogen eclipsing the carbonyl). The equilibrium constant for cis conformation ⇋ gauche conformation is 0.7 at 37°C. For 3-methyl-2-butanone, however, no conclusion can be drawn from our data. Possible reasons for this difficulty are discussed.