What is the difference between 그런데 and 그러는데??
Is 그런데 the contracted form of 그러는데??
If not, how are two of them different from each ohter??

Question

Answer

Both are vastly different:
그런데: by the way
그러는데: according to [someone]; given to that

그런데 집에는 언제 갈 거야?: By the way, when are you going to go home?
엄마가 그러는데 오늘 저녁은 외식할 예정이래: According to mom, we are going to eat out this evening.