Balsamic chicken, marinade?

So I was making balsamic chicken and I did something that I don't normally do, I added balsamic vinegar to the marinade. I don't think I got it all off when I put it in my cast aluminum skillet but I didn't think it would be a problem. Although the chicken turned out wonderful, there was some REALLY dark areas on the esge of the breast. Since balsamic vinegar has sugar in it...was it the sugar that burned? is balsamic vinegar a recommended ingredient in marinades?