Bis(tetramethylcyclopropylidene)methane (I) was prepd. by treating 1-(dichloroethenylidene)-2,2,3,3-tetramethylcyclopropane with Me3CLi and Me2C=CMe2. The parent allene II was obtained from bis(1-bromocyclopropyl) ketone by treatment with low-valent Ti. Both I and II show unusually intense allene stretching bands in the IR spectra, and the signals of their central C atoms appear at remarkably high field in the 13C-NMR spectra. The unique structural features of I and II, as evidenced by an x-ray crystal structural anal. of I and 1JCC values, agrees remarkably well with theor. predictions made by semiempirical (MNDO) and ab initio (4-31G) calcns. and on the basis of the simple picture offered by the hybridization model using the iterative max. overlap (IMO) approach.