Allenes This is a class of compounds that contain a C-C=C bonding unit. H H The middle C is sp,and the outer two C's are sphybridized. The two contiguous n bonds must lie perpendicular to each other for p orbital overlap-thus the ends of an allene are perpendicular. HC CH3 CH3 C=C=0 H H H Penta-2.3-diene is chiral even though there are no chiral atoms. Ch5 Stereochemistry (landscape) Page 15 Ch05 Stereochemistry (landscape) Page 15 Allenes This is a class of compounds that contain a C=C=C bonding unit. The middle C is sp, and the outer two C’s are sp2 hybridized. The two contiguous  bonds must lie perpendicular to each other for p orbital overlap – thus the ends of an allene are perpendicular. Penta-2,3-diene is chiral even though there are no chiral atoms