If anything it may even help you to take them in the summer as it is a heavier workload (same material compressed into a shorter time) as long as you did well in the course. Would you be taking full-time courses during the summer or just the o-chem? B's aren't bad.. it's more of how it fits into your overall GPA. It's not as if they say "OMG look they got a 'B', *DENIED*." It would be more like, look they only got B's (= a 3.0 GPA) which is sub-par in terms of looking competitive, but far from completely damming to your ability to get into the school of your choice.