Aromatic Radical Anions with Parallel or Crossed Triple Bonds

Proton hyperfine data are reported for the radical anions of 1,8‐di (propyn‐1‐yl)‐naphthalene (I), 7,8,12,13‐tetradehydro‐10,11‐dihydro‐9 H ‐cyclodeca[ d , e ]naphthalene (II) and 2,2′‐di(propyn‐1‐yl)‐biphenyl (III), as well as of 5,6,11,12‐tetradehydro‐7,8,9,10‐tetrahydro‐dibenzo[ a , c ]cyclodecene (IV) and its 8,8,9,9‐tetradeuterio‐derivative (IV‐d 4 ). The triple bonds in I and II can be regarded as roughly parallel, while those in IV (and IV‐d 4 ) may be considered as crossed. The π‐spin distributions in I⊖ to IV⊖ are discussed in terms of simple MO models which suggest a weekly bonding interaction between the acetylenic fragments in IV⊖, in contrast to III⊖ where such an effect appears to be negligible. The importance of an analogous interaction in I⊖ and II⊖ is difficult to deduce, since its inclusion into a MO model does not substantially affect the π‐spin distribution in these radical anions.