There's nothing on the standard check-in form to say "no connecting door." The only way to request that is to call (or have your TA call if you booked through one) and have that request put on your reservation.
I'm like and hate connecting rooms. I put that on my touring plans request for Contemporary. We went to room and it was connecting BUT when I saw TPV we stayed. Honestly unless you saw door you wouldn't have known it was connecting. There were people in room and we never heard them! Know that is rare as we've had horrible connecting rooms.