methyl resonance (not shown) is a doublet at 1.37 ppm vs. DSS and has a spacing of 6.0 Hz. Of the three protons remaining on the propylenediamine backbone, it appears that Ha produces the triplet-like resonance at highest field, and that Hb and Hc are almost coincident at lowest field. The triplet-like resonance of Ha results from spin coupling to Hb and Hc with nearly equal magnitudes (/ab « -12.5 and /ac 11.0 Hz).6•7Simultaneous irradiation of cobalt-59 and the methyl doublet leads to changes in the low-field portion of Figure 2B which are consistent with the assignment of Hc. The approximate chemical shifts are ¿a ~2.48, ¿b ~2.93, and ¿c ~3.05 ppm vs. DSS. Use of solvent shifts and a higher spectrometer frequency spreads out the spectrum sufficiently for a complete analysis, now in progress.The sharpness of the Ha lines compared to the Hb lines tends to indicate that the Co-N-C-H coupling constant is greater for equatorial protons than for axial protons. A similar result is evident for Co(en)31 23+ in Figure 1C.21 This finding, in addition to the fact that ¿b > Sa in L-[Co(( -)pn)3]3+ supports the assignment of ¿axia¡ <~2.75 ppm and ¿equatorial ~2.93 ppm in Co(en)33+.
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