Help with shape keys for a beginner, please! anyone?

I know there are other ways to accomplish this, but In my case I need to do this simple task with shape keys!! no ways around it in my case.
I know shape keys causes deformation. What i need to know is how do i go by editing in between shape to fix it the best i can and I will move on…

I need the movement in one animation only (a single shape key). thank you!!

A better way to state the shape key issue is to say that the vertices are interpolated linearly from each of the two keys. So strictly speaking, with a single shape key (and a base key) there is no way to get the mesh to appear to rotate.

you can use multiple keys
you could just keyframe rotation on the object or use an armature
you could skrinkwrap the end verst to a hidden arc

Photox is correct – shape keys are linear. You should add a bone to the rotating piece.