There is a semantic difference between the two. The straight quote is a superset of the curly one. So "rock 'n' roll" is correct. And "rock ’n’ roll" is correc

There is a semantic difference between the two. The straight quote is a superset of the curly one. So "rock 'n' roll" is correct. And "rock ’n’ roll" is correct. But "rock ‘n’ roll" is not correct, since the wrong apostrophe is used. We're not quoting the letter n, we're showing that the letter a was removed.