So what I want to do is teach you guys tests for the two most common ones, which are allenes and substituted biphenyls, and the other ones don't really need rules, so you're fine. You can just always assume that they're going to be chiral. However, it turns out allenes and substituted biphenyls can be chiral, or they cannot be chiral depending on the rules they follow. So let's look at this. We are simply going to use a modified version of test two, which is the one for stereo centers, to identify trigonal centers in the allene. But you might wonder about the two double bonds. Well, here is the tricky part: we are going to visualize the allene as just one big double bond. Maybe squint a little bit and try to see it; try to ignore the carbon in the middle and just pretend it's one big double bond. By the way, this is just my way of solving these, but I think it has helped a lot of students, and I believe it will help you too.

If it can form E or Z isomers after visualizing it as a big double bond, that means it's chiral. Remember when I taught you guys about trigonal centers, I mentioned that they're actually achiral if they pass the test. But allenes are different, so just think about allenes as their own thing. Allenes are going to be chiral if they can form E or Z through this weird long double bond. So, I'll do the first one with you guys, and then I'll let you guys do b and c on your own.

Here's what I would do: look at this compound and ignore the "c" in the middle, just pretending it's one big double bond. Then, I would ask myself if this double bond is able to form E and Z, or cis and trans. Since I have two of the same atom on one carbon, on one side, it actually cannot form E and Z, or cis and trans. This means that no matter how much I switch these two groups, I'm never going to be able to get E and Z. So, this one would be achiral. Now, I want you guys to solve further and use this knowledge to determine the chirality in other cases.