Many schools require you to have at least 6 -8 credit hours in Organic Chemistry (although yes, there are some schools that only require 4 credit hours in organic), so it would be beneficial for you to take orgo 2. Additionally, orgo 2 material will be covered on the DAT, so you will have to go over that material anyways. Although you can take the DAT if you just self-study orgo 2 material, I think it would be a little more difficult and you would have to have good discipline to go over the material on your own. But since there are schools that require more than 4 credit hours in organic, I would advise you to take orgo 2. You can apply to schools only having taken orgo 1, but you will need to take orgo 2 before you matriculate for the schools that require it.