The Determination of the Stereochemistry An Undergraduate Organic Experiment Alex T. Rowland Genysburg College, Gettysburg, PA 17325 The determination by chemical means of the configurations a t centers of chirality in the threo- and erythro-isomers of most (u-dvcols and related compounds is no easy chore. Attention-has been focussed in recent years upon the use of NMR spectroscopy in making the appropriate confieurational assignments in cyclic derivatives of'ihecompounds. One report utilizes the detection of an intramolecular nuclear Overhauser effect (NOE) or W-type long-range coupling in the 'H NMR spectra ol'the acetonide, oxau~lidine,or thiazolidine derivatives to make the assignments ( I ) . An earlier study demonstrated the feasibility ofthe use of IH NMR spectroscopy in characterizing numerous symmetrical and unsymmetrical erythro- and threo-glycols hy examination of the corresnondine acetonides (21. For several years we have conducted a first-year organic exneriment which illustrates the Dower of 'H NMR soectroscopy in a configuration determ'ination of the type c;ted. T h e structure involves the reduction of henzoin (1) with sodium horohydride' (NaBH4) followed hy conversion of the resulting diol (11) to the acetonide [a 2,2-dimethyl-4,5-diphenyl-1,R-dioxolane (Ill)]. ~
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The sequence provides a fine o.p.~ o r t u n i t vto correlate a number of puints with topics covered in organic lectures. Experience is pained in the use of NaRH6, a reagent employed routinely as a reducing agent in the latest organic lahoratory manuals ( 3 )and discussed in detail in all orpanic texthooks. The projection formulas and the various conformations of the (Ila) and its threo erythro (li,S)-I,2-diphenyl-1;2-ethanedi~1l (SS.RH) isomer (Ill)) serve to emphasize the stereochemical aspects of acyclic systems. The f
