How to name this organic molecule?

Ok, this is NOT homework. Well, it is tangentially related, but… well, I’ll explain. Our teacher gives us sheets of MS/NMR/IR data from time to time to take home and analyze, and come up with a structure for. Usually not that complicated. My standard approach is to find the structure, name the compound, and then try to find it on Aldrich’s website, where they have the NMR for various things. The only problem is that I can’t name this damn molecule.

Description beginneth:

Ok, imagine a cycloheptyl ring. Now replace a C with an O. Now add a double-bonded O to a neighboring carbon. What you have now is like a cyclic ester, with 7 members, including the O. What is the naming convention for things like this?

Assuming I understand your verbal description correctly, it sounds like a lactone that one might call 6-hexanolide. Been a while since I had organic, so grain of salt on that one. Let us know what you come up with.

Since I’ve been having WAY too much fun playing with it… have some IUPAC naming software.

Registration required to DL, but it’s a free program. It says it’s oxepan-2-one.

Yes, the correct IUPAC name is oxepan-2-one. (It’s 2 because the carbonyl group is considered to be at the 1-position; the oxe- indicates that there is an oxygen atom at the 2-position.)

You can find the IUPAC rules for naming lactones here. This page suggests the alternative name ‘heptano-7-lactone’, which is also correct.

The name oxepan-2-one is generated according to the Hantzsch-Widman rules, which you can find here. In this system, the name for a saturated 7-membered ring ends in -epane, and the presence of an oxygen atom within the ring is indicated by oxa-. Thus, a 7-membered ring with an oxygen atom is ‘oxepane’. The carbonyl group is indicated in the usual manner, hence oxepan-2-one. The alternative name, heptano-7-lactone, would be easier to recognize for someone who wasn’t familiar with the Hantzsch-Widman rules, though, so it might be a better choice. OTOH, it’s easier for naming software to use the H-W rule than to recognize that the compound you’ve provided is a lactone.

We aren’t dealing with 7 carbons, are we? I thought the OP described a 7-member ring and then said one of the members was an oxygen.

I think you’re right, it should be hexano-6-lactone. The IUPAC lactone-naming link Roches provided shows a 5-member ring analagous to the OP’s molecule, and it is named butano-4-lactone.

Well, thanks for the help, guys, but I can’t seem to find an NMR of this damn thing anywhere. At least I’ll look intelligent when I go to my chemistry professor for help. :slight_smile:

I found the C-13 shifts for butano-4-lactone in Spectrometric Identification of Organic Compounds, by Silverstein, Bassler and Morrill, p.271:

(ppm from TMS solvent):

  1. C(=O) 177.9
  2. C (adjacent to CO) 27.7
  3. methylene C
    C (betwee

sorry, the message posted before I could finish!

C-13 NMR of butano-4-lactone (ppm in TMS):

  1. C(=O) 177.9
  2. methylene C, adjacent to CO 27.7
  3. methylene C 22.2
  4. methylene C, adjacent to O 68.6

Presumable the two additional methylene carbons in your hexano-6-lactone will have shifts similar to #3 above.

Nope, unfortunately, that’s not it. Grrrr.

If it helps, here’s some data.
C NMR: [ul]
[li]176.2[/li][li]69.3[/li][li]34.6[/li][li]29.3[/li][li]28.9[/li][li]22.9[/li][/ul] [ul]
[li]4.25 (2H)[/li][li]2.65 (2H)[/li][li]~1.6-1.9 (6H)[/li][/ul]

This just bothers me because I can’t. figure. it. out.

Obviously, that second list is proton NMR, but I guess I didn’t type that because I was trying to get the list to come out right. :smack:

Yes, it should be hexano-6-lactone; it’s a seven-membered ring with only six carbons. (I really don’t know why I made that mistake, especially since I drew 6-hydroxyhexanoic acid in the process of getting the name.) That means it’s a cyclic ester of 6-hydroxyhexanoic acid, and the IUPAC rules seem to indicate that the number in the name of a lactone should be taken from the location of the hydroxyl group in the hydroxycarboxylic acid.

If you wanted to be really annoying, 6-hydroxyhexanoic acid probably has some trivial name that you could use. The trivial name for hexanoic acid is caproic acid, so you could call the lactone η-caprolactone. There are actually Google hits for this outdated name, most of them from industry.

If you want estimated 1H and 13C NMR data, I could post them. You might also want to try this site in addition to Aldrich’s – it’s the one I mostly used. It has the compound you’re looking for, BTW, with another name: 6-hexanolide (CAS 502-44-3).

Try one of these references. If not, youll have to dig through Chem. Abstracts. Youve certainly picked a reasonable structure given the NMR.

Bui, A. M.; Cave, A.; Janot, M. M.; Parello, J.; Potier, P.; Scheidegger, U. Isolation and structural analysis of collybolide, a novel sesquiterpene extracted from Collybia maculata. Carbon-13 NMR of lactones. Tetrahedron (1974), 30(11), 1327-36. CODEN: TETRAB ISSN:0040-4020. CAN 81:169647 AN 1974:569647 CAPLUS\0

Ichikawa, Yukihiko; Matsuo, Taku. Solvent effect of the chemical shifts in nuclear magnetic resonance spectroscopy. III. Benzene solutions of cyclic ketones and lactones. Bulletin of the Chemical Society of Japan (1967), 40(9), 2030-4. CODEN: BCSJA8 ISSN:0009-2673. CAN 68:6832 AN 1968:6832 CAPLUS\0

McFadden, W. H.; Day, E. A.; Diamond, M. J. Correlations and anomalies in mass spectra. Lactones. Anal. Chem. (1965), 37(1), 89-92. CODEN: ANCHAM

Ok, I went and talked to him, and he said that it didn’t matter that the NMR shifts were off by a couple of ppm, and that my proposed structure was reasonable. :confused: :cool:

Thanks for the reference materials, though. :slight_smile:

Well, these are the 13C data from the SDBS site for 6-hexanolide:

   176.22   449      1  (carbonyl group)
   69.30   918      2 (methylene group adjacent to O)
   34.57  1000      3 (methylene adjacent to C=O)
   29.34   952      4 (4-position)
   28.93   845      5  (5-position)
   22.99   831      6 (3-position)

These match chaoticdonkey’s data exactly, so the structure is right. There’s no 1H NMR on the site, but there’s MS and IR (liquid, nujol mull, carbon tetrachloride, KBr disc), so you should be able to positively identify the structure from the carbon NMR and IR data. (I assume you got an IR because it would make it much easier to determine that the structure is a lactone…)

Oh, durrr. Thanks Roche. When I saw the data above, I thought it was for the molecule that I needed.

And yes, I did have an IR. How can you differentiate a lactone from other things on an IR?

I don’t mean to quibble, but according to 77th Edition of Handbook of Chemistry and Physics the compound you describe is listed as “2-Oxepanone” or "“Caprolactone”. This compound is number 8590 in the “Physical Constants of Organic Compounds”.

Waterman: IIRC, the CRC Handbook of Chemistry and Physics uses ACS names, not IUPAC names, so you get 2-oxepanone instead of oxepan-2-one. I presume ‘caprolactone’ is a valid name under the ACS rules also; it seems to be the name used in industry.

The name ‘6-hexanolide’, BTW, is from an older set of IUPAC recommendations (the 1979 Recommendations) which also provides for ‘caprolactone’ formed from ‘caproic acid’. The 1993 recommendations don’t include the first rule, and the 1993 IUPAC recommendations don’t retain ‘caproic acid’ as a trivial name for hexanoic acid; thus hexano-6-lactone.

chaoticdonkey: Lactones show a C=O stretch absorption that depends on the size of the ring. My book (J. Lambertet al., Organic Structural Spectroscopy) only gives absorptions for β,γ and δ lactones: 1850-1830, 1780-1770, and 1750-1730 cm[sup]-1[/sup], respectively. In the nujol spectrum for your compound, the lactone C=O stretch is at 1725 cm[sup]-1[/sup]. Since other carbonyl compounds can have absorptions in this range, you can tell that it’s a lactone more by the peaks you don’t see and by the chemical formula. The formula should be enough to deduce that it’s a ring; otherwise, you can tell it’s a lactone because there’s only one C=O stretch and because there isn’t, for example, a peak suggesting a carboxylic acid or a hydroxyl group.