Experimental Section Proton magnetic resonance spectra were obtained with a Varian HA-100 nmr Spectrometer or with a Varian A-56/60A spectrometer equipped with a Varian C-1024 time-averaging com- puter. The probe on the A-56/60A spectrometer carried a dewar- jacketed probe insert which could maintain stable temperatures as low as - loo", 80 that low-temperature, time-averaged spectra could be obtained with no great difficulties. The ...
