Barr's class was the worst class, no the worst experience of my time here at UCLA. The material that this class covers could and should constitute a fairly relaxing class. None of it is overly complicated or difficult in and of itself.
However, Barr somehow manages to make this likely one of the worst classes across every UC. The false confidence that you are given from the extremely simplified and surface level lectures is instantly annihilated by the slaughterhouse that is the first midterm. IF you manage to escape and survive the darkness of this valley, there is no true peak to be found. Just as you start climbing the other side, the floor falls out below you and you plummet into a pit of pure torture, the second midterm. No matter how much you prepare for a midterm with the same difficulty as midterm 1, you will not escape this impending doom. (The average of this midterm was in the low 60s and was not curved).
While this pattern could also somewhat be found in Shao's Chem 20A class, the final provided an oasis at the end of the quarter. Barr did not. The final was the worst test by far. Barr said himself, and I quote, "This one is a doozy." Now, if you are still considering taking this class, note that it is not just the tests which are bad.
To save time I will list the rest of my complaints in bullet point fashion.

-No answers to any practice problems unless you go to every "optional" office hours
-Not even TAs were given all of the solutions
-Office hours by Barr were far too slow and rarely got to difficult concepts
-Some people had to retake this class for scoring too low on the final even though their overall grades were high C's to low B's (would not budge on bumping people 1% up to the bar(pun intended))
-Group homework assigned Friday night and due early Monday morning
-Assignments on about 50 different websites which are very easy to miss
-Somehow make you feel like its all your fault

Don't take this class. I know you have to. But don't. Take it at a community college if you have to.
Only advice I have if you are unfortunate enough to take this class:

-realize GPA isn't that big of a deal
-go to TA office hours

Im sorry

Like many others, I was allured by the veneer of understanding Dr. Barr has. The initial emphasis on mental health and wellbeing was supportive all well and good until tested. His empathy seems to extend quite far in his speech until the actual exam. Besides the convoluted absurdities asked on the exam, and his unwillingness to scale, even in a global pandemic when people are taking the class online in every time zone, for freshman general chemistry! That's not very empathetic. I cannot imagine a general chemistry class being unscaled at a university like UCLA. However, I wanted to give him another chance for the second exam because I was thinking he would listen to student feedback, but as I suspected, absolutely no changes were made in the manner in which the questions were asked. Much of the lectures are filled with superfluous, unnecessary speech which makes chemistry (an already difficult enough subject) all the more complicated. The "systems" of the class are overly complicated and unnecessary. There are two portals for surveys, homework assignments are collaborative without any decision made by the student. It is clear that we are the first round in a new-age type pedagogy and it's not working. The only good thing about this class is the GroupMe, where it is a community of 500 students all bonding over the constant suffering of this class, and collective outrage at many aspects of this course. Do not take this class!!

No matter how much you study, it won't be enough. The midterms are very difficult and all application questions with probably more biology concepts than chemistry. On top of this, Barr is extremely stubborn and does not even take into account the surveys he makes us do. I just do not understand how this is allowed, ESPECIALLY BECAUSE THERE IS NO CURVE! He claims that he is "empathetic" to us because we are in troubling times, but then he troubles the troubling times by giving us exam questions we know nothing about.

Pros:1. The professor seems like a nice person

Cons: 1. The tests are little related to review sessions, homework, and lectures
2. No curve
3. No extra point
4. Feel like chemistry is so scary
5. Really frustrating feeling when taking this class

Advices for people want to take this class: don't put so much time on review sessions because then you would find out that you are "studying for a different exam".

The chem department as a whole just does not care for its students and Professor Barr is just a product of that. He tells us that he can't give 24 hour exams because "his hands are tied" and "it's what the department has mandated". This would be fine if this was true because then he truly couldn't do anything. However, this is all a lie. The Chem Labs give 24 hour exams and I heard that the Chem 20BH get 24 hour exams. He also told us that the first midterm would be easier than the homework. Again another lie. Lying to his students is just one of the many things that I don't like about this class. The other thing I do not like about the class is that in our discussions, the TA's and the LA's try to be as helpful as they can be but what is the point if you aren't going to test us on the things we've been studying. Professor Barr also likes to say that he "empathizes" with our situation. He can say it as many times as he wants but if he does nothing to address the many issues that we students come to him for, then he might as well say nothing at all. He does not accommodate for international students either. Even when you spend the extra time to go to his Office Hours, he barely helps you and instead gives you an answer that just leaves you with more questions. Again Professor Barr is just a product of the Chemistry Department not caring. After someone in the class sent an email to the department begging to understand the reason for all of this, the department implied that Barr is a great professor and very qualified. Ahem I don't know if being very smart makes you qualified to teach but I guess I wouldn't know since I'm a student. But I guess the department wouldn't know either since they can sit at the top and act so aloof. You can't ask a principal to understand the struggles in a classroom because they never sit in there day in day out so how would you expect the "prestigious" Chemistry Department of UCLA to understand the struggles of a student in a global pandemic mind you. I hope that Professor Barr does at least try to learn from all this because there is hope, but the way he is right now... avoid him.

WORST CLASS EVAAAAAAA!!! There was more focus on encouragement than teaching chemistry. He wasn't tolerant and didn't care about anyone's personal issues, such as getting covid. He made it way more difficult to learn than it had to be by never giving answers and sometimes gatekeeping information in his lectures. The class was always treated like elementary students. He actively tried to hide answers and "encourage collaboration" where it wasn't helpful. He used multiple different websites and apps throughout the course making it difficult to keep up with the work. Barr would barely answer specific questions on material and proceed to put that same material on exams. He makes the most complicated test questions about random real life products/events which are difficult to answer with the little teaching he gives on those certain topics. His borderline creepy obsession with Disney has also ruined any good experiences I ever had or will have with that company. I never want to take a chemistry class again and especially not with a teacher that talks about helping his students so much when he is actually inhibiting our learning with the ways he hides information and answers from us. I never want to see anything related to buffers, acids, or bases again out of fear for the PTSD it will bring from this horrendous class. This man's purpose of making the class more difficult than it should be seems to be overshadowing his passion of teaching and ruins any chances of easily learning. His tests progressively got harder while switching from online to in-person which became really difficult with less notes allowed in person and more challenging material. Never taking a class from him again and god forbid anyone else has to either. FUCKIN WEIRDOOOOO!

My opinion on Barr pretty much aligns with everyone else's. I honestly think that he's a nice guy who cares about teaching, which automatically makes him better than a lot of other professors, but he's just so new and it takes time to iron out a teaching and test writing style that works. There is a lot of mandatory group work, and I got very lucky with an excellent group so that ended up helping me a lot, but it's all up to chance and I understand how people could be mad about that. I actually felt that the workload of the course was pretty light, with only 4 homework assignments due in the quarter graded by accuracy and weekly pre-lecture activities that hold your hand the whole way through. The two midterms felt like the extra challenge problems at the back of a textbook that no one likes, just too detached from the material to feel fair. I felt like the final was a very big improvement over the midterms (probably due to people complaining in his emails) with much more straightforward questions, and if you scored better on the final than one of your midterms then he counted your final score twice instead of that midterm, which was cool. I feel like all of these negative reviews will be kinda pointless in like a year as I think he will improve very much, but if there are other professor options with good reviews then I can't recommend Professor Barr over them in good conscience.

The group you get in is probably the most important thing. I tried to change my group at the start of the quarter but thanks to the TA that did not happen. Then, I had to do all 4 homework by myself for the whole quarter. Barr's a nice dude but you'll hate him for the way he designs his 20B class.

Lectures:
Barr seems knowledgeable about chemistry, and his lectures might be helpful if you already have a decent knowledge of the course material (maybe if you took AP Chem). If you do not have a working knowledge of what he is talking about, you will probably be left behind. The lectures themselves seemed to make sense, but he often skipped steps, making simplifications when solving problems that he seemed to assume we would understand despite him never really explaining them. Take good notes. Anything helps.

Homework:
The OWL assignments seemed easy enough, and we had more than enough attempts at each problem to get 100% and get a brief understanding of a few topics. However, they were very short assignments and the problems were nowhere near the difficulty of tests. They were helpful for a first look at concepts, but don't use them to study. It won't help.

The Textbook:
If you took 20A, it's the same one. I would use ChemLibre or Organic Chem Tutor instead.

Tests:
DIFFICULT. Study. He writes them himself and they won't be what you expect. The questions are mostly pretty fair if you really understand the material, but there are multiple reach questions per test. For example, stretching the course material to apply it to current topics in biology, theoretical questions about geology, etc. They are also timed with a strict submission period. He also includes material that he teaches on the same day as the test.

How to Study:
Do the problem sets. I wish I would have done them every week when they were released. They are long, but are really the only way to study. Unfortunately, he won't give you an answer key, so you'll have no idea if your hours of work were going in the right direction. Make sure you have some kind of study group to ask about pset questions and try to make a group answer key. Problems at the end of the textbook chapters would probably also be helpful if you have any time to do them after finishing the problem sets. Also, watch Organic Chemistry Tutor on YouTube and use ChemLibre. They explain things a lot better if you need it.

Empathy?:
Barr constantly says that he "empathizes" with students, but he won't do anything to help them. I think this happened in basically every lecture. Most notably, he insisted on only having one time for tests for every lecture and time zone. Like every student in any lecture took the test at the same time. It worked for me, but some of the international students told him that they would have to stay up late to attend the lecture and then wake up at like 5am for the test. He said he was very "empathetic", then proceeded to do absolutely nothing about it, continued to include material from the same day's lecture on tests, and made no effort to find a way to make the timing work better. This kind of thing happened a lot. He seems to want to appear empathetic, but it's not very genuine.

Grading:
You need at least a 68% in the class and a 50% on the final to pass. Your final grade can replace one midterm. That sounds good, but definitely don't count on doing well on the final. The one redeeming factor of this class was that it seemed like tests ended up being a relatively small portion of the final grade. If you get over 50% on all the tests you should get a C. Based on a poll we did in the group chat it seemed like most people passed, so that's good I guess?

Barr is one of the few professors who really seemed to care about his student's learning. He often gave surveys to students to asses how effective his lectures and assignments were and made an honest effort to improve and implement suggestions. In addition, he and his TAs had multiple office hours every day, so if you were ever confused on a topic there was always an opportunity to ask somebody. The midterms were certainly a stretch, with many of the questions requiring you to take what you learned in the class and apply it to a novel situation. This meant that the midterms were much harder, and even if you knew all the material perfectly you could still stumble as you have to apply the materials in new ways. However, to counteract the difficulty the midterms have a group component, allowing you to get many test points by going over the midterm with your group and resubmitting it. The final was much more normal and easier, with straightforward questions that covered the content (and it replaced a midterm score). Discussion sections made you go through questions with your assigned group, which provided good studying material as the questions were similar to test and PSET questions. The way his class is graded is somewhat confusing as he refuses to give a straightforward curve, he instead says that points gained from (rather easy) HW assignments and points from the surveys act as a "curve". I disagree with having the midterms be so difficult, but the final is reasonable and the rest of the class is filled with many opportunities to learn and improve. (NOTE: This was his first class as a professor, he stated multiple times that he was evaluating his course and technique and planning on implementing changes, so his future courses may be different than what we experienced)