Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: a_ht on October 25, 2005, 03:53:52 PM
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How does one invent a new molecule so that, on paper, it has desired properties. What do I need to know to get started?
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minimum organic chemistry.
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It's very difficult to predict the properties that a molecule will have before you actually make it. Most pharmaceutical research is based on little more than a couple of leads and a lot of work. They typically find a structural motif that gives a desired effect and then vary substituents all over the molecule to try to optimize the effect. Sometimes they don't really have any idea how the molecule is interacting with proteins, etc. in the body.
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A lot of discoveries in chemistry are either accidental or through following other people research. Atleast that's what I've inferred from reading things.
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"accidental" being used very loosely.
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Combinatorial chemistry may be worth researching, it was quite popular a while back and is still used today.
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A lot of reactions were discovered as "side reactions" to other know reactions and then optimized under slightly different conditions to favor the different reaction pathway. It's hard to do because most chemists just dismiss the side products of reactions as junk and don't give them a second thought.
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Ill just make a polymer! Where can I find detailed reference information about bonding properties of "bonds??" - Photoreactivity, bonding strengh, what makes a molecule soluble, volatile, whats gives polymer a particular shape, etc. How can I find that type of information?
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Ill just make a polymer
what type of polymer?
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There are different types? One composed of 2 isomers. 1 isomer breaks when subjected to UV light. The other isomer is reserved for future properties.
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http://en.wikipedia.org/wiki/Polymer
:) :)
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organic photreactivity is very interesting. Any text in physical organic chemistry should go over it. Look for the pericyclic reactions chapter.
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There are tons of different types of polymers. Their properties vary not only based on their molecular structure, but also based on many other superstructural and external factors. The poly-dispersity (the range of polymer sizes, usually by MW), the addition of non-polymerized external molecules (so-called plasticizers) which are used to tune the polymer for hardness, flexibility, etc., and the overall denisty of the polymer are also important. You can also have copolymers where you have polymerized two different monomer units into one polymer. These can be either alternating monomer units, random, or block copolymers where the two (or more) units are polymerized in separate "blocks" along the larger polymer. You can also make cyclic polymers where you make one huge polymer ring; these often have different properties than linear polymers of similar size. Cross-linked polymers are very important. I cross-linked polymers, linear polymer chains are attached to one another through chemical bonds. These are often very rigid polymers.
On a molecular level, the stereochemistry of nearby atoms can have large effects on the macroscopic behavior of the polymer. Generally you can have either random stereochemical arrays, alternating R/S, or single stereochemistry (e.g. R only) polymers. Some of the macroscopic properties of polymers can be predicted based on known polymers with similar structures, but again there is a lot of trial and error involved in finding the kind of polymer you want!
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This weekend, I want to sit down, grab a pen and sheet of paper and start drawing my molecule (writing the little symbols and the OH, H-C=C-H thingy). I need to know where I can find the numbers. Are there no books or online resources that publish the properties of different isomers? And what their properties are when combined? What do you guys use in the industry, the physic and chemistry handbook doesn't seem to give all these details. Are there no reference material that you use? All I can find on the net is introductory and tutorial material... I need the next step, which is accurate relevant information about the known isomers and their properties.
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The whole thing about chemistry is that the product is very different then the some of its parts. So, you can't add 2 fragments together and know the chemistry of the combined fragment. That being said people in the field can readily do this because they are experienced with this stuff. Like I said in my first post, if you read an undergraduate organic chemistry book from start to finish you would have the knowledge to make the first attempt at something interesting.
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Experienced chemists can predict the behavior of new molecules by analogy to known molecules which have similar functional groups. For example, I could take acetic acid (a smelly compound which is acidic, relatively high boiling, miscible with water) and react it with an alcohol, say ethanol (also miscible with water, not a strongly scented, polar, not acidic or basic to an appreciable extent) and react the together to make ethyl acetate, an ester which is not miscible with water, boils lower than acetic acid, but slightly higher than ethanol, has a sweet smell, and has no appeciable acidity or basicity. I could predict the behavior of ethyl acetate because I am familiar with esters; I can predict the behavior of ethanol because I am familiar with alcohols; I can predict the behavior of acetic acid because I have dealt with carboxylic acids before. Since I have experience with all these, I can predict the reactions they will undergo and how I could potentially isolate the product. Once you know how to deal with molecules containing certain functional groups then you can extend that knowledge to molecules that haven't been made before. You just need to know how certain functional groups behave.
For example, I recently made a compound that no one had ever made before. It contained a ketone, an alkene, and a nitrile. Things get a little more confusing with multiple functional groups, but in this case it wasn't too difficult. I knew this compound would not be very volatile because the alkene and the carbonyl group were conjugated (these enone compounds are typically much higher boiling than their ketone counterparts) and I knew that the molecule would be relatively polar because of the nitrile functionality. So even now I have no idea what the boiling point of this compound is, nor any of its biological activity, but I do know how to make it and how I can isolate it from the by-products of the reaction. It's all about having experience dealing with compounds.
It's not always this easy. Sometimes functional groups undergo unexpected reactions with one another. This can't be avoided and it's always a possibility. You have to learn what kinds of functional groups are definitely not compatible. This also comes from experience. For example, I would never propose a molecule that contained an unprotected primary amine and an acid chloride. The two functional groups would reaction rapidly. Again, experience is the name of the game.
Bear in mind that even experienced chemists don't always know what to expect. Some compounds that look perfectly reasonable on paper might be impossible to make in the lab. Paper chemistry can often be deceptively easy! You can predict a lot based on what you know about other compounds, but the level of certainty is invariably low.
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I am going to ask one more time because I do not know how to be any more clear than this. Where do I find information about the properties of (isomers / functionnal groups / dentrimers / chemical bonds / macroscopic properties / what ever you call these) on the internet or in books. A title or a good link is all I need.
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I am only going to answer this one more time. Get an organic chemistry book and read!
http://www.chemicalforums.com/index.php?board=3;action=display;threadid=2414
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I am going to ask one more time because I do not know how to be any more clear than this. Where do I find information about the properties of (isomers / functionnal groups / dentrimers / chemical bonds / macroscopic properties / what ever you call these) on the internet or in books. A title or a good link is all I need.
try typing "chemistry" into google :D