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.
Hand Tighten First. Hand tightening is almost enough to seal the joint sufficiently to prevent leaks. Cross-threading is an issue, so hand tightening also lets you know whether the threads are not lining up correctly. If the joint does not screw together easily, thereâs a good chance the threads are crossing.