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.
* indicates required. The Linen and Threads' Cross Stitch Corner Gauge is a new cross stitch tool to help you determine where to start stitching. The wooden corner gauge measures 3 square and has 3 starting points (2, 2 1/2 and 3) depending upon your framing allowance. Mark your starting spot with a pin and you are ready to begin stitching your project.