Abstract. CsH9OzBr, monoclinic, P2~/c, a=6-383 (4), b=ll.180 (6), c=11.430 (7)A, /~=95.76 (3) °, Z=4, D~= 1-78, D,,= 1.76 (2) g cm -3. C8H902I, orthorhombic, Pbca, a=11.825 (6), b=15-609 (25), c= 11.310 (7)/~, Z= 16, D¢=2.05, D,,,=2.11 (5) g cm -3. The bromolactone, and both independent molecules of the iodolactone, exist in the 2,6-bridged configuration with normal bond lengths. The bond angles, however, show considerable departure from their ideal values. The angle at the bridging carbon atom is 94.8 (4) ° for the bromolactone and 103 (2) and 101 (2) ° for the two molecules of iodolactone.Introduction.