Cycloserine is an antibiotic isolated from the microbe Streptomyces orchidaceous. It is used in conjunction with other drugs for the treatment of tuberculosis.
(h) Draw all significant resonance structures of cycloserine.
Alright guys, let's look for significance resonance contributors to our molecule, just start up by drawing it up, we have an oxygen nitrogen, here we have an NH2 and then at the top we have our carbonyl and of course this hydrogen right here, so let's take a look, well, let's first draw our lone pairs, we have one, two, three, four, five and six, so let's first start by drawing one resonance contributor, right? Where we start by drawing this double bond, let's show that that pi bond actually brings these electrons on to that O and now that O has an extra lone pair on it. So, by doing so what we would've got is this, first copy this compound here over here. Now if we've done that what we gonna get is, let's take away one of these bonds and now add on a new lone pair to our molecule, okay? So this is one resonance structure that we can draw but it's not complete until we draw in the charges, we have a negative and a positive okay well, what do you guys think is that? it is that the only resonance structure? whenever, we have a charge adjacent to a lone pair, right? And that lone pair we are talking about is not this one, right? We can draw an x, that's not adjacent, we have this lone pair that we are talking about, okay? So this lone pair is actually delocalized on our molecule, what that means is we are gonna actually show resonance there, so what we can do and now again copy the structure, I'm going to paste it right here and now we are going to show that this lone pair is right there, what we can do is now take the electrons, right? this lone pair make a bond there and in doing so what we get is, let's actually draw on this structure here, make a lone pair there, we are going to get a new pi bond. So, here is our pi bond and now where that charge is gonna go? Well guys, we no longer have these electrons, right? Because we just used them, so this nitrogen right here is going to have a positive charge and now, what do you guys think, can we actually draw another structure? because remember what I told you, we had a lone pair adjacent to a positive charge in this structure, right? We have a lone pair adjacent, okay? So, next to a positive charge and we say that that would allow this lone pair to delocalize on our molecule, well, take a look, we have a lone pair adjacent to a charge, so it must be our resonate but take a look. Notice that if we actually showed a resonance structure what we'd get is if we bring this here. Notice that our molecule now, let's just redraw the whole thing, we now have a double bond to this N, right? And there's an H there. Now, notice that N only has four orbitals, so it can only make, our nitrogen can only make four bonds, so this would not be a significant resonance contributor, we could actually stop right here and just say, we only have one, two, three possible resonance structures for our molecule. Alright, guys well, hopefully that made sense.