An X-ray structural study of two gem-dihalosubstituted triangulanes, possessing linear fragments of spiroannulated cyclopropanes, allowed us to work out an empirical calculation scheme describing the geometry of triangulanes. The crystal data for 1,1dichlorotetraspiro[2.0.0.2.0.2.0.1]undecane (C~HI2-C12, M r = 215.1) measured at 173 K are: P1, Z = 2, a=6.729(2), b=9.176(2), c=9.490 (3) A, a= 94.49 (2), fl = 107.42 (2), 3'= 103.12 (2) °, V= 537.7 (6)/~3, Dx = 1.33 g cm -3, Mo Ka radiation, A = 0.71069 A,/., = 5.56 cm-l, F(000) = 224. The final agreement factor was R=0.027 for 2501 unique reflections. The crystal data for 1,1-dibromopentaspiro[2.0.0.0.2.0.2.0.1.1]tridecane (CI3HInBr2, Mr = 330.1) measured at 183K are: P1, Z=2, a = 7.433 (5), b = 9.508 (6), c = 10.120 (9) A, a = 111.69(2), fl=93.81(6), 3, =100.23(5) °, V = 647.1 (8) A 3, Dx = 1.69 g cm-3, Mo Ka radiation, A = 0.71069 A,,/z = 61.7 cm-t, F(000) = 324. The final agreement factor was R = 0.047 for 2987 unique reflections. Abstract ( -)-3,4-Di-O-acetyl-1,2,5,6-tetra-O-benzyl-myo-inositol, C38H4oO8, Mr=624.7 ('jumping crystal'). Three monoclinic crystal forms. Form I, T= 18 °C, P21/n, a= 28.883 (3), b= 15.189 ~!,, c =