Question: We will be installing a single under mount sink with garbage disposal. Converting from the current double basin sink.
I'd like to tackle this project if possible. My idea was to cap the right existing side, shorten the pipe coming out of the disposal and move that to the middle, where the new sink hole will be. I am also planning on purchasing new garbage disposal, but that should not affect anything.

Hoping everything will align. Does anyone see an issue with this approach ? Attaching the existing photo and also marked up photo of what I'm proposing to do.

[![enter image description here](https://i.stack.imgur.com/K0nao.jpg)](https://i.stack.imgur.com/K0nao.jpg)

[![enter image description here](https://i.stack.imgur.com/42FSS.jpg)](https://i.stack.imgur.com/42FSS.jpg)

Answer: 
Don't cap. Don't cut.

Remove everything before the trap. The new disposal will come with an L-shaped tail piece that comes out then down. The new disposal and the existing trap can both be rotated. Use the new tail piece and rotate them both. I'm pretty sure they will align. If not, try shortening (cutting) the 90 degree bend coming OUT of the trap, or else get a tail piece extender.

[![enter image description here](https://i.stack.imgur.com/MTurm.png)](https://i.stack.imgur.com/MTurm.png)

That AAV should be higher. Ideally higher than the highest water level in the sink. But lacking that, at least higher than the drain. You have to hope the new disposal's exit is no higher than the existing one. If it is, you'll have to raise the AAV. That's glued in so you'll need to cut it all out and do the whole thing from scratch.
Looks like this is what you have, and what you need.
[![enter image description here](https://i.stack.imgur.com/X7MCE.png)](https://i.stack.imgur.com/X7MCE.png)
Don't forget that the disposal can be rotated 360º!

And don't forget to remove the knockout from the disposal's dishwasher hookup!