THE PROTON MAGNETIC RESONANCE SPECTRUM OF CYCLOPROPYLAMINE, THE A2A2′X CASE WITH STRONG CROSS-COUPLING: A PSEUDO FIRST-ORDER SPECTRUM WITH COMBINATION LINES

By means of the anisotropic solvent effect of benzene on the ring protons of cyclopropylamine the proton spectrum is converted to A2A2′X. Since the cross-coupling from the A2 to the A2′ protons is large the spectrum does not approximate to a pseudo first-order AX4 spectrum. Instead, it is one which may be described as pseudo first-order with combination lines. The presence of the latter allows a fairly complete set of coupling constants to be derived in a simpler way than by a computer attack on the general A2B2X spectrum. Conversely, the approach developed here, when applicable, allows the derivation of reliable input parameters for a computer program. From the temperature dependence of the A2A2′X case the A2 and A2′ protons can be distinguished and it is found that the protons trans to the amino group are preferentially shifted to high field by the benzene molecules.