[classicfan]

Hello, everyone!

I am analyzing the molecule ethyl acrylate right now and having a little trouble because I've, unfourtunately, fallen behind in my organic chemistry course at the moment.

I'm having a little trouble understanding this whole thing, so any help is appreaciated.

First off, ethyl acrylate does not have any Z or E bonds, right? There is the one double bond, but I don't think it's Z or E, 'cause the carbon  binded to OCH₃ and double bonded to O has the highest priority, and all the remaining H's have equal priorities, right? So we don't have neither a boat nor a chair conformation, hence no Z or E. Am I getting it right for now?

Secondly, are there any sp³ chirality centres on the molecule? I don't really get this one, but is the carbon double bonded to an oxygen an sp³ chiral carbon, with an R configuration? Or is it not a chiral centre at all, since it's not attatched to four different groups? Are there any other chirality centres that I missed?

Finally, are any parts of the molecule conformationally mobile and what is the most stable conformation of ethyl acrylate? Unfourtunately, this part I'm really lost with and can't think of how to answer.

Please, help me with this analysis.

Thank you very much in advance

[Scatter]

You're asking a bunch of different questions all at once, but for the most part, you should follow your intuitions.  I'm not going to just answer everything, but a couple important points that I know are correct that I can tell you:

Chiral centers do indeed need 4 different groups.  When speaking of chirality, double bonds count twice, so it would be as if the carbon in the center was bonded to two Oxygens (this is not literally true, but for chirality determination you can think of it that way).

If you have the double bond at the end of a chain like this, it will be neither E or Z because the hydrogens at the end have equivalent priorities.  What if there was a C-O single bond at the top and the CH-C bond to the left of it was actually a CH-C double bond (with the bond to the left of that being a single CH3-CH bond)?  Would that be designated E or Z then?  It would be helpful to practice a lot of these problems.

[classicfan]

Sorry, I AM a little all over the place with my questions, but that is only because I was trying to analyse it as I am typing and so I could make sure I have the right thought path when answering these kinds of questions.
Thank you, you've cleared up a few of my uncertainties. And I'll certainly practice more of these questions, as sooon as i have the time.


One thing about the chirality centres - does H count as a group? So the left carbon double bonded to another carbon and single bonded to the central carbon also count as a chirality centre?

[Scatter]

Out of curiousity, why were you speaking of boat and chair conformations?  We've only learned those terms in respect to cyclic molecules (rings), specifically six carbon rings.  Like I said, I'm curious because I could see how a two dimensional representation of a four carbon alkene could look like a chair or a boat.

[classicfan]

Out of curiousity, why were you speaking of boat and chair conformations?  We've only learned those terms in respect to cyclic molecules (rings), specifically six carbon rings.  Like I said, I'm curious because I could see how a two dimensional representation of a four carbon alkene could look like a chair or a boat.

Oh, we also analyzed cyclic molecules from a cis and trans point of view, but before we got into any of that we looked at linear molecules that have this property. From 2-D point of view it IS possible to see a cis or trans conformation, right? Well our prof told us we had to look at that feature of it when describing our molecule (mine is ethyl acrylate), so that's why I got into the boat/chair discussion.

[Scatter]

One thing about the chirality centres - does H count as a group? So the left carbon double bonded to another carbon and single bonded to the central carbon also count as a chirality centre?

H does count as a group.  So if you have a C with two H's or just an image of a molecule with a C with a single bond to another C on both sides--and that's it, that middle C is not chiral (because of the two H's...they may or may not be pictured...usually not).  For example, if you have CH3 bonded to a C bonded to a C bonded to an OH or something, that second C can be chiral if there's a hydrogen and one additional bond to it that isn't only a -CH3, -C-OH, or -H.  Get what I'm saying?  Groups can be considered any atom or chain of atoms, functional group, ring etc. but the atom that you're looking at as the center can't have any of these groups be the same in order for it to be chiral.

[Scatter]

Out of curiousity, why were you speaking of boat and chair conformations?  We've only learned those terms in respect to cyclic molecules (rings), specifically six carbon rings.  Like I said, I'm curious because I could see how a two dimensional representation of a four carbon alkene could look like a chair or a boat.

Oh, we also analyzed cyclic molecules from a cis and trans point of view, but before we got into any of that we looked at linear molecules that have this property. From 2-D point of view it IS possible to see a cis or trans conformation, right? Well our prof told us we had to look at that feature of it when describing our molecule (mine is ethyl acrylate), so that's why I got into the boat/chair discussion.

Sure you can see cis and trans with two dimensional images.  I just haven't heard boat or chair talked about this way.  Makes sense though.

[classicfan]

Sure you can see cis and trans two dimensionally.  I just haven't heard boat or chair talked about this way.  Makes sense though.

I don't really know, chemistry's not a strong point for me, so i could be making a mistake or using the wrong terms. I just used "boat" and "chair" cause that's what I remember from high school and it was just the way my train of thought went. But really those two terms, as well as cis and trans shouldn't be used cause they create confusion when talkign about linear (at least) conformations. I should have stuck to just E and Z.

[classicfan]

Get what I'm saying?  Groups can be considered any atom or chain of atoms, functional group, ring etc. but the atom that you're looking at as the center can't have any of these groups be the same in order for it to be chiral.

Understood. Another question (so sorry for bombarding you like this, i just really want to understand this topic), what is the difference between an sp₃ chirality centre and just a chirality centre? Is it that the sp₃ means it has to have a tetrahedral shape? Or is the shape ethyl acrylate have also allows for an sp₃ chirality centre?

[Scatter]

I'd rather leave the majority of this question to another person because while I understand what you're asking, I don't understand how to completely describe it to you.  I can say that organic chemistry revolves around Carbon, which generally forms 4 bonds.  The most stable conformation of a carbon bonded to four other atoms is a tetrahedral shape, meaning sp3 hybridized (~109.5 degree bond angles).  Chirality deals with symmetry (or rather, the lack of symmetry...a symmetrical molecule is said to be archiral).  In a chiral molecule, there is no plane of symmetry, which is why the emphasis on four different groups.  I would look in your textbook for discussion on orbitals in relation to this.   You can have chiral centers with other atoms than carbon I think, which would mean less or more bonds than 4, but this is where my knowledge on the subject ends at this point in time.  Interesting stuff though...

[Borek]

One thing about the chirality centres - does H count as a group? So the left carbon double bonded to another carbon and single bonded to the central carbon also count as a chirality centre?

H counts as a group, but double bonded carbon is NOT connected to four dirrefent groups.