The synthesis of six unsymmetrically substituted tetraarylporphyrins is reported. The compounds prepared are 5‐(R),10,15,20‐tritolylporphyrins, where R = 2‐pyridyl, 3‐pyridyl, 4‐acet‐amido, and 2,3 or 4‐hydroxyphenyl. Four new tetrasubstituted tetraarylporphyrins (5,10,15,20‐tetra‐(R)‐porphyrin) are also reported, where R = 3‐pyridyl, 4‐acetylphenyl, 4‐hydroxyphenyl and 4‐butoxyphenyl. The proton nmr spectra of these porphyrins are presented.

The crystal structure of a cubic modification of tetracyanoethylene has been studied. The space group is Im3 and the cell edge is 9.736 (5) .~. The bond lengths agree well with those in the monoclinic modification, but there are significant differences between the bond angles in the two forms. The central C=C bond is 1.344 (2) • which is not significantly different from the corresponding bond length in ethylene and considerably shorter than predicted from INDO calculations. A new double-atom refinement method has been applied which, from the X-ray data alone, corrects for the apparent shortening of the C=N bond length, as previously found by comparison of X-ray and neutron diffraction data. The corrected value for C=N (1.166 (2)/~) is close to the electron diffraction result on tetracyanoethylene. The molecular packing in the crystal is such that large cavities surround the positions (0,0,0) and (½, ½, ½).

stretching frequencies are high, indicating that tt back-bonding may be minor, a similar argument may be used. On replacing the platinum methyl group trans to the carbonyl by a chloro substituent, v(CO) increases from 2085 to 2104 cm-1 while 5C(Carbonyi) changes from 178.7 to 159.3 ppm. Concomitant with the in-8583 creased carbon-oxygen bond order is an increased paramagnetic screening of the carbon nucleus.

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