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Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

15. Analytical Techniques:IR, NMR, Mass Spect

Purpose of Analytical Techniques


Reason for Analytical Methods

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Hey guys, it's great to be back with you. My name is johnny and welcome to our section on analytical techniques. Before we even get started. I just want to kick off by answering the question that I'm sure you all have at home. Why do I even need to learn this? So back in the beginning of time when organic chemistry first started becoming a thing, scientists started running into an issue pretty quickly, which was one I'm designing all these cool reactions. All my test tubes are turning colors. But how do I know that the reaction is actually working? How do I know that I'm actually getting the right product to when I go to buy my synthetic precursors. My benzene is my settle Aldo hides all those molecules I need so I can make bigger things. How do I know that? I'm actually buying the right molecule and I'm not just buying like a bucket of garbage. Well these are questions that scientists needed an answer for relatively quickly. So they started developing a line of chemistry that we call wet chemistry or sometimes called bench chemistry. These are the literally the liquid reactions that you see. Those crazy professors do on tv and they were originally just used to verify what molecules we had. Okay, so here's a really common example Tolins test. This is a molecule. I'm sorry. There's a reaction that you might recognize from organic chemistry lab if you haven't seen it yet. You probably will at some point in the year. Okay. And this is a common test. Very classic test that test for the presence of Aldo hides in a compound in a solution. Okay. Now, usually what we're trying to do is we're trying to differentiate, is it a ketone or is it an AL to hide? So what they do is they put the mixture into the test tube then they add silver oxide. Okay. And that silver oxide, I'm not sure if you guys recall is an oxidizing agent. So it's going to go ahead and add an oxygen to the alga hide oxidizing it. But most importantly, it's gonna create a silver mirror that's going to precipitate out of the solution. And you're actually gonna see that the walls of the test tube become silver. Pretty cool. So even though this sounds like a nice parlor trick to take home to your family, I'm gonna explain why it's not really that useful one. First of all, you need to have the re agent sitting around, you need to have that silver oxide in your lab or you're never going to know if you have Allah guides. Right? So that's already limiting. That means you're gonna have to carry a lot of different re agents. Okay, um to, it's not very reliable. It turns out that This reaction can actually work with some ketones, it actually could oxidize some ketones. So a lot of these wet chemistry reactions have exceptions. They're not really the most reliable tools. 3rd and most importantly, it's not very specific. It doesn't tell me the exact type of Alfalfa height I'm getting. It just tells me do I have an alga hide or not? It doesn't tell me the length of the carbon chain. It doesn't tell me if there's two albo hides, not one, it's literally very little information that I'm getting. So as hundreds of reactions were being developed every year, scientists needed a better way to know what molecules they are producing. Now. By the way, you might just be thinking, why not use a microscope, johnny guys remember these molecules are so small that no microscope, especially back in the day, could ever ever see what's going on at that level. Now we have electron microscopes that can see at a much smaller level but still, it's not that's not a good tool for confirming what molecules you have. So what is a good tool? Well, that brings us to modern methods of identification or what we call dry chemistry. Okay, so in general, these are gonna be big expensive machines that your university has spent millions of dollars on just to answer this one question of what molecule do I have in front of me right now. Okay, so here's a good example of an an an analytical technique. It's called proton NMR. Okay, this is just one of the several analytical techniques that are, As you can see. It's such a big machine that someone can actually stand on top of it. Alright, and you can imagine how expensive that is and what it does is you put molecules in it and it spits out this mess of peaks and troughs and spectrums and bumps and all this stuff. And as scientists we are supposed to write scientists and training, we're supposed to be able to take this information and convert it into a molecular structure. Okay, now that might sound like a really hard thing to do, but you'd be surprised how much better it is to be looking at this kind of information than it is just to use a bunch of different test tubes and and dry and I'm sorry and re agents to figure out what you have because these peaks, these traps these these spectra can give us a world of information more than you could ever get through wet chemistry. Okay, so in this section we're gonna be going through some of these analytical techniques and I'm gonna be teaching you guys how to take crazy information like this and turn it into usable information that you can use either in your lab to identify what you have. Okay, that actually is an assignment you're probably gonna have this year. You probably will have to identify a molecule based on NMR based on IR one of these analytical techniques or to just to answer questions on your exam because guess what? This is something your professors care about and they want you to be able to do on your exam. Okay, so that being said, that's kind of the intro. Let's go ahead and get more into detail on some of these analytical techniques.