Change the following condensed structures to Kekulé structures...

Question

Change the following condensed structures to Kekulé structures:

a. CH₃NH(CH₂)₂CH₃

b. (CH₃)₂CHCl

Accepted Answer

Hi, everybody. Let's take a look at the next problem. It says give the correct kekule structures for the following condensed structures. And we have two different condensed structures given to us. So we need to recall what are kikue structures. These often get confused with Lewis structures. But Kikui structures show lines for bonds and show all bonds between atoms and that includes carbon hydrogen bonds. So as you can imagine these get a bit unwieldy and large, sometimes these show lone pairs and formal charges. Um when kikue invented these structures or came up with this notion of representing molecules, the electron hadn't been discovered. So they weren't there originally, but of course, are useful for modern scientists. So you can still have a kule structure that has long pairs or doesn't it can go either way. This is as opposed to Lewis structures which represent all electrons including bonds between atoms as dots. So in a Lewis structure, and if you had a bond between atoms, you would show two dots between those two atoms. Whereas in a kikue structure, any bond you replace instead of the dots, you have a line between the two atoms. So let's look at our molecules here. For number one, we have CH three NH and then in parentheses, ch two subscript two C and then in parenthesis, ch three subscript three. So we start with a terminal methyl group. So let's draw our carbon. And again, in kikue structure, we show all the bonds. So this has three hydrogens and we draw all three hydrogens with lines coming off of our carbon. Then this is the next we have NH so that would be a nitrogen. So our carbon, we draw a line going to n this nitrogen has one hydrogen. So we draw a line to h and then it just has one hydrogen and then it has, we see we have ch two in parentheses with the subscript two. In this case, this isn't a substituent of our nitrogen, but it represents that there's two repeating CH two units. So let's draw a line from our nitrogen to another carbon. This is ach two unit. So this carbon has two hydrogens bonded to it. So a line on top and a line on bottom and then a second ch two unit. So just repeat that. Then next, we have a carbon with three methyl groups attached to it. So this is going to get very big. So we have a carbon and then we draw a line up to another carbon. This carbon has three hydrogen surrounding it kind of squeeze those in. Then down below, we have another methyl group. So carbon with three hadrons attached and at the end, another methyl group, so carbon with three hydrogens attached. So again, we have ch three at the beginning, this methyl group to start off N with one hydrogen, then the two ch two units. And then finally, our isopropyl group is carbon with three methyl groups. So that's our structure for our first condensed structure. I can see how they get very big very quickly. Now again, we can show lone pairs are not, but to be thorough, let's represent them for the most thorough structure possible. We know looking around that our hydrogens just can make one bond. Every hydrogen in the structure has one bond, carbons usually make four bonds. And we can see our various carbons all have four bonds each. So it won't carry any loan pairs, but nitrogen has five valence electrons. Our nitrogen here has three bonds representing three of its valence electrons. It's got two left. So we're going to represent that going to represent that as a lone pair on the nitrogen. So two dots above that N we can also again to be really thorough represent formal charges, the carbons and hydrogens here all have neutral formal charges in having the number of bonds we expect for the nitrogen to calculate a formal charge. We look at the number of valence electrons which is five minus the number of non bonding electrons, which is two and then minus the number of bonds since one electron each participates in the bonds, three of those gives us a formal charge of zero. So no formal charges here in our structure. Now, let's look at molecule number two. So this one is CH three ch and then in parenthesis, ch three ch two cl. So we'll start with our terminal methyl group. So we draw c with three hydrogens attached, it's attached to ach then with parenthesis ch three. So this would be a carbon with a methyl substituent. So we've got a line from our carbon to another carbon. It has one hydrogen and one methyl group. So below, we have an H above, we have carbon and that carbon has three hydrogens sweetest those in there. Then we have ach two CL. So from our second carbon in the chain, draw another carbon then that has hydrogens on top and bottom. And then finally, a bond to a chlorine atom at the end. Now, do we have any lone pairs here to be thorough? Well, our hydrogens all have one bond, each of our carbons has four bonds. So no lone pairs there. Our chlorine just has a single bond while chlorine has seven valence electrons. So we would have three lone pairs to add six more valence electrons. So we'll put this long pears on there does anything of a formal charge. Again, our hydrogens and carbons normal amount of bonds, no formal charge. Chlorine has seven valence electrons minus six that are non bonding minus one bond. So formal charge of zero, no formal charges on the structure here. So there we have our KK a structure for our second molecule. And again, just representing every bond present even the carbon hydrogen ones by a line, you see this shows us the bonding, the connections but also gets a bit big and unwieldy with especially with all the hydrocarbon groups there. See you in the next video.

Change the following condensed structures to Kekulé structures:
a. CH₃NH(CH₂)₂CH₃
b. (CH₃)₂CHCl

Key Concepts

Kekulé Structures

Condensed Structural Formulas

Functional Groups

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