Carbocations are species bearing a formal + charge on carbon. The have sp2 hybridization and trigonal planar geometry, with an empty p orbital on carbon, perpendicular to the plane containing the substituents (see diagrams shown to the right).
Aortic cross-clamp. An aortic cross-clamp is a surgical instrument used in cardiac surgery to clamp the aorta and separate the systemic circulation from the outflow of the heart. An aortic cross-clamping procedure serves, for example, in the repairing of coarctation of the aorta.
Cross elasticity of demand is defined as the percentagechange in the quantity demanded of one good divided bythe percentage change in the price of another good. Twosubstitute products normally have a positive cross elasticityof demand. Two complementary products normally have anegative cross elasticity of demand.6.