Matt posted:Can I just check that the second pair of sentences, where the prepositional phrases come at the end of the sentence are also grammatically correct?
Yes, Matt, your second pair of sentences are grammatically correct, but they are extremely awkward. If I were you, I would not advise your students to use them.
The "President of the United States" example I gave is ungrammatical with the relative clause coming before the "of"-phrase. "Of"-phrases tend to be special.