Deuterium exchange at various positions on the C2B4H8 molecule has been studied. D2 exchanges with all boron-bonded hydrogen atoms, and B2D6 in the presence of diglyme exchanges only at the 4 and 6 terminal positions. The (CH3)2C2B4H6 and DCl exchange, catalyzed by aluminum chloride, occurs at both apex and base terminal positions. 2,3-Dicarbahexaborane(8)-2,3-d2, D2C2B4H6, has been prepared by heating B5H9 with C2D2. The infrared spectrum is given and it is shown that there is no migration of deuterium from carbon to boron during the synthesis. © 1968, American Chemical Society. All rights reserved.