Structural Formula - Video Tutorials & Practice Problems
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1
concept
Molecular Formula
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Now, molecular formulas are insufficient for organic compounds because they do not convey convey structural information. Now, structural information itself gives us an idea about the connectivity of an organic compound as well as the orientation elements take when they bond to each other within that organic compound. Now connectivity is how atoms are connected to each other orientation. That's gonna be discussed later on when we talk about um stereo isomers. But for right now, let's not worry about it. Now, molecular representation here we have our molecular formula of C two H 60. This structure can be drawn in a couple of ways. C two H 601 potential way of drawing this is having our two carbons connected to each other. And then we're gonna give hydrogen to these, to these carbons. Remember carbon ideally wants to make four bonds. So far, we've used both carbons and five hydrogens. What we have left is an oxygen and a hydrogen. We could then write an oxygen connected to this carbon and then place on it the remaining hydrogen. So this is one potential structure from the molecular formula. Now there's just not enough information. Um just from this molecular formula because we could also draw it as are two carbons, each connected to the oxygen in each carbon having three hydrogens. Technically, either one of these structures are correct. If we're only given the molecular formula, as you can see, we don't have enough information to know for sure which one of these two structures the person might want. Right. So that's the limitation. When it comes to molecular formulas, we might know the number of elements, but we don't know how they're connected to one another and what their orientation would be in terms of space. All right. So just remember this is one of the limitations when it comes to molecular formulas.
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example
Structural Formula Example
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Here in this example question it says which of the following statements is incorrect about molecular formulas and molecular structures, right? So molecular formula and structures show which atoms are present in a molecule. That's true. If we have a formula of C 2860, I know that there's two carbons, six hydrogens and one oxygen. So this is true, molecular structure cannot be used to calculate molecular weight. This is incorrect if I know a number of elements from C 2860 I can calculate the weight of that compound. This is our answer. Molecular formula is sufficient to show the composition of a compound. Yes, because you'll know the number of each element from that. You'll know the percentage each one represents within that given organic compound molecular structure shows how atoms are connected to each other. Yes, you can draw out how those atoms are connected to one another through the use of our molecular structure, right? So this is true. So out of all the options, option B is the one that's incorrect.
3
concept
Structural Formula
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Now, a structural formula shows how atoms in a compound are connected or bonded to one another. Now, it's the same as a Lewis structure except we do not show lone pairs. So if we took a look here at this structure, if we wanted to draw the Lewis formula, we'd remember that the oxygen has two long pairs on it. When it comes to our structural formula, we don't need to show the presence of those lone pairs on oxygen because we're more concerned on the bonds that are being created between our different atoms. We don't care about non bonding electrons, which is typical with a Lewis dot structure, right? So just remember both of these are showing how atoms are connected to one another or bonded to one another. But Lewis does a little bit more by showing us our non bonding electrons or loam pairs structural formulas don't really care about that.
4
example
Structural Formula Example
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Here, it says to draw a structural formula for C two H six. All right. So this molecule compound has two carbons within it. We can show these two carbons bonding to one another. Now, we have six hydrogens and two carbons to keep things fair. Each one can get three hydrogens a piece. Now here, this carbon would have three hydrogens and this one would have three hydrogens. This comes out to be our structural formula for C two wave six. And in fact, this is the only structural formula we could draw. Remember, hydrogens can only make one bond. So we couldn't put any of them in the center, which means our two carbons must go in the center carbon ideally wants to make four bonds by drawing it this way, they're all making four bonds, which means we cannot draw a double bond between them or a triple bond because that would exceed the four bonds that carbon ideally wants to make, right. So this would represent our structural formula for C two H six.
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Problem
Problem
Propane (C3H8) is a component of liquified petroleum gas. Draw a structural formula for propane. (Hint: Carbon makes four bonds.)
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Problem
Problem
Methylamine (CH5N) is a gaseous compound with a fishy smell. Draw this molecule using structural formula.
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