I’m doing this organic chemistry assignment on spectroscopy - IR, carbon and proton. I’m kind of stumped on one question, and I can’t seem to find the information I’m looking for in order to find out if my “possible structure” for the given data is even remotely close to correct. I’ve tried Google, but either I suck at searching (very possible) or the information is kind of obscure (which is why I’m DEFINITELY going to discuss this with classmates and/or prof on Monday!).
Can anyone tell me where epoxide carbons would be found on a 13-C NMR? Although my structure isn’t really an epoxide (I don’t think. It’s an R-C=C-R’ , where the two alkene carbons are bonded to the same oxygen. Is that still an epoxide, or does the name change? Epoxene?
I would think (read:hope) that it would be somewhere between the -C=C- and the C=O regions, say around 150-160ppm? Although simple C-O carbons are lower, in the 50-90 range.
Can anyone help?
Thanks! mnemosyne, who is also trying to figure out how an integration of 11 can be right for a C9H12O compound…arrrggghhhhhhhhhhh!!!
Best bet is calcualte it yourself from them big books on how to calculate NMR data (with the tables and the looking around). Or if that fails do a search using a chemical search engine (beilstein for example) for a compound that contains the same structure and find a link to an NMR spectra of it.
As to an integration of 11 for a compond that could be 12, did you aquire the spectra yourself? If so don’t take the integrations as gospel as the can be effected by bad shimming, too much noise, screwy window functions etc. If you were given the spectra as part of an assignment then they’d more than likely fix it so thast 12 was correct.
A little clue though, R-C=C-R where the R = the same oxygen is impossible (or damned unstable) think about the pi bonding orbitals they have to at 180° to the C=C bond, your suggesting a 60° angle. (to be fair though i left organic behind a few years ago).
What spectra have you been given? as a rule of thumb that i used for this sort of stuff IRs or only given to show C=O’s and OH’s and NMR is the daddy for structural work (EI-MS will point you at he molecular weight and possible fragments).
Your proposed structure is a three membered ring with doublely bonded carbons and an oxygen? I do not think that is possible in a stable molecule. Three membered rings are very unstable to begin with, add a double bond into that ring and I doubt you would ever see it anywhere other than as an intermediate. You wouldn’t be able to collect enough of it to do an NMR.
I kind of realised last night as I went to bed that the structure doesn’t make all that much sense. But given what I had sorted out, I was left trying to incorporate two carbons and 16g/mol of something (so I figured oxygen) without having any hydrogens, since the H-NMR we were given didn’t have any “more” available. We didn’t take any of these spectra ourselves - it’s just an assignment sheet. We have an IR, and both types of NMR to go by, but either I remember nothing from college and I can’t read my textbooks properly, or something doesn’t quite add up. For example, both the IR and the H-NMR DEFINITELY point to a ketone, but there is no carbon in the >200ppm range, which is where ketones should be, accoding to my class notes and text book, as well as a few online listings (not to mention the prof!)
I’m thinking now that it just might be a carboxylate, even though the H-NMR peak would be a little bit low (at 9.5 rather than 11-13ppm). If that’s the case, then maybe I’m reading the IR wrong, and the ketone evidence isn’t totally there (it’s a REALLY bad IR - looks like someone drew it in MS-Paint). That said, I still have a couple of carbons to fit into the rest of what I know, and the whole thing has to weigh 124g/mol. The only way I can think of to fit 2 carbons and have no hydrogens would be as an alkyne. But there are no C-NMR peaks at 60-90ppm.
I’m not expecting you to do this homework for me, but maybe you’re beginning to see why I’m so confused!
As for the Integration of 11 comment, that’s another question in which all we have is both types of NMR, the IR, and the molecular formula of C9H12O. I know its aromatic, I know its disubstituted, I know it’s an alcohol - I’m just missing a hydrogen somewhere and I don’t know where to put it (because obviously that would affect the structure that I propose).
This assignment is driving me nuts!!!
Thanks anyways
If the Hydrogen is attached to an oxygen in an OH group you might have trouble detecting it (it’ll be broadened out to buggery and depending on solvent may not be observable, say it’s in 2H2O (deuterated water, can’t do damned sub and super scripts in HTML) it’ll exchange and therefore be NMR silent).
By the way, 13C and 1H are not the only types of NMR, any nucleus with a spin 1/2 or over 1/2 can be detected and looked at (although with spin greater than 1/2 they get more confusing).
31P and 15N are useful spectra too you know! (biochemical NMR spectroscopist here!)
Not strictly true. Oxirenes have been isolated, but only in solid argon matrices, although I agree that this doesn’t really meet any useful defintion of stable.
It’s a sweeping statement to say that three membered are very unstable. They may appear to be highly strained, but kinetically they’re surprisingly unreactive and very easy to handle. Boil them up in solvents, store at room temperature for years, they’re fine.
Maybe next year. This is only Organic II (3rd year). We don’t get to actually do much on our own until Org III. I’m taking that next semester, as well as Organic Reactivity. Should be fun
I actually think I have the structure solved - it’s a butadiene with wacky substituents (well, not so wacky, I just don’t want to try and name it now). ALthough I’m second-guessing the location of the oxygen - I have an ethoxy group, but it might actually be part of the ring, making it 5-membered.
wow by quoting your text i can [sup]also[/sup] learn to do such [sub] things [/sub]
How’s lie treating you then? (sorry to turn this into a chat type forum). I was suprised it took you so long to put a reply into this thread, surely off all threads you have a NOESY at (deliberate mis-spelling, an NMR joke for any other chemists out there) this would have been a prime contender to check?
Anyway as another aside
I was thinking about this, do you have one peak that intergrates to 11 with comparision to one that intergrates to 1, or is the total number of peaks an integer of 11? (remember that multiples of numbers are allowed)
There were a bunch of peaks that, when you measured and integrated and did all the easy division to get the ratios of hydrogens, came out to 11. Part of the question told us that there were 12 Hs in the compund. So I had to figure out where the “missing” hydrogen was. Turns out the integration on the benzene ring was just plain wrong. Despite the fact that it came out to 4, it really should have been 5. It’s just that when we hand in these problems, we have to show all our evidence, positive and negative, and it was driving me nuts that the math wasn’t working out.
It’s all good, though. Besides, it’s handed in, and over until the final (no spectroscopy on the midterm, since it can take a while to do even if you know exactly what you’re doing!). Although I like Spec. It think it’s cool how everything all works out. I cant wait til next semester when we get to actually do things ourselves! I really do enjoy organic chem. My TA thinks Im weird, cuz I’m actually a biochem major, taking a lot of extra org classes in the next couple of years (Org III, Reactivity, Synthetic Organic, etc). Guess I’ll get into bioorganics or something like
