I haven't used this -accelerator option, but have used various bindings to get this sort of behavior. Maybe this is obvious, I don't know know, but I've tripped on this "landmine" before!

The issue is whether or not your GUI application can even get the CTL-N to begin with! This will not happen unless your app window "has mouse focus". When you are testing this, click on the "title bar" of the Tk app before you test entering CTL-N. Also, for debugging, put something like -command => sub{"print ctl-n received\n";}. If you can get this working with mouse focus on your window and want this to work without mouse focus, then a "higher level" of keyboard mapping needs to occur and that is possible, but happens at the overall window manager level rather than at the object level.