The major isomer in 25 and 75% isomer mixts. of isophoronediamine (I) and of isophorone diisocyanate was a chair conformation with cis orientation of the equatorially oriented NH2(or NCO) and CH2NH2(or CH2NCO) substituents. The structure was studied by 1- and 2-dimensional NMR and confirmed by x-ray structure anal. of a single crystal of the I main isomer. The I single crystal has a space group P.hivin.1 and cell dimensions a = 5.864(2), b = 8.107(3), c = 11.505(5) .ANG., a = 87.63(3) Deg, b = 88.85(3) Deg, and g = 73.34(3) Deg.