The assignment of proton hyperfine splitting constants in benzo [cd ] pyrenyl has been discussed with the aid of some variants of McLachlan's method and blcConnell's relationship. The proton hyperfine splitting constants for benzo [cd] pytenyl (fig. i) have been determined by Reddoch and Paskovich [ I ] very recently. Their assignment of the constants was based on McLachlan's method [2] and the McConnell relationship [3].
Unfortunately the authors have erroneously interchanged the calculated spin densities of positions 3 and 5. Therefore according to their approach the assignment of the constants equal to 5.25 G and 5.54 G should be exchanged with each other.
It was found, however, for neutral odd alternant hydrocarbon radicals [4,5] that Zhidomirov and Schastnev's modification of the McLacl'flan method (formula (17) of ref. [4] ) yields a definitely better agreement with experiment than the original one and the other methods. The conclusion is not altered by the most recent calculations carried out by Tifio [6] and Wasilewski [7]. Therefore we have decided to discuss the assignment of the splitting constants in benzo led] pyrenyl more closely again.
Results of the McLachlan method and its modifi-