A Hundred and One Rules in Arabic Grammar!

  1. Long vowel to a Diphthong. ==============================

If any of the two long vowelو , ا ** ** is proceeded by the short vowel**–َ** ** ** , the long vowel changes its character to a diphthong:

uu --->  ou    دَور ، دور

ii   --->  ei   **دَين  ** ** ** ، دين