Organic Chemistry (CHEM301/302)
Khan Academy videos can be super helpful. https://www.khanacademy.org/science/organic-chemistry
Leah 4 Sci has some great study sheets to help you drill reactions. http://leah4sci.com/
Calculus
This is a great site for math help. They have many examples and problem sets that are great for practice. http://tutorial.math.lamar.edu/