When analysing NMR spectra, every student at one time during their chemistry studies learns about vicinal coupling and that it produces the characteristic signal shapes of proton spectra. The following multiplets are usually taught and considered consensus:

  • singlet (s)
  • doublet (d)
  • triplet (t)
  • quartet (q)
  • multiplet (m)

But that doesn’t even adequately cover all hydrocarbons; quintets and septets need at least be considered. If, furthermore, there are heteroatoms with a half-integer spin of larger than $1$ present, not even these will suffice.

In my lab experience, I often came across a septet of doublets, which ACD termed sptd. However, I just found an internet source proposing the abbreviation sepd.

Is there a consensus on how coupling patterns with more than four of one coupling should be abbreviated? If so, what are the official abbreviations?

  • $\begingroup$ ACS guidelines for authors are not very helpful. My personal experience in standard organic synthesis is that anything beyond quintet is not reported as such which shouldn't be happening now that powerful software is widely available. $\endgroup$
    – K_P
    Oct 16 '15 at 19:35

There is no absolute consensus for reporting abbreviations for splitting patterns. Even Magnetic Resonance in Chemistry, a journal that I generally take as the best guide for reporting NMR data, does not have recommended abbreviations for multiplicities above quartets. Further, there are general inconsistencies in reporting formats within this journal, with abbreviations such as s, sept, spt being used for septet. Additionally, the actual term used to describe the splitting varies. For instance, both pentet and quintet are commonly used to describe a 1:4:6:4:1 splitting.

What is consistent, however, is that the abbreviations are defined within the paper.

Commonly used terms and abbreviations that I have come across include:

singlet (s)
doublet (d)
triplet (t)
quartet (q)
pentet (p, pent, pnt, pentet) or quintet (q, quint, qui, qnt, quintet)
sextet (sext, sxt, sextet)
septet (s, sept, spt, septet) or heptet (hept, hpt, heptet)
octet (oct, octet)
nonet (non, nonet)

While splittings of higher multiplicity are less common within mainstream $\ce{CHN}$ organic molecules (septet for isopropyl substituents are a common exception, and 'apparent' splittings are excluded), they are more common with heteronuclear substitutions and organometallic systems, where spin numbers greater than 1/2 are frequently encountered. Reporting 'apparent' splittings of, say, $\ce{(CH3)2C}H\ce{CH2R}$ as a nonet (where $J_\mathrm{ab} \approx J_\mathrm{ac}$) is not strictly correct according to the $2nI+1$ rule, although in non-NMR journals still occurs, and is certainly taught at undergraduate NMR level.

As for reporting multiple couplings (doublet of septets, for example), again there is no strict rule to adhere to, although the commonly adopted practice is to report the larger coupling first. So, a doublet coupling of $\pu{10Hz}$ and septet coupling of $\pu{2Hz}$ would be a doublet of septets. If it were doublet $(\pu{2Hz})$ and septet $(\pu{10Hz})$, one would report a septet of doublets.

  • $\begingroup$ Thanks for this answer, likely the one I will accept. Personally I am well aware of the rules you highlighted in your last paragraph and the last sentence in the last but one paragraph, but they will very likely help future visitors. The case which prompted this question was a septet of doublets I frequently encounter thanks to an isopropyl group with ~7 and ~3 Hz for the septet and doublet respectively ;) $\endgroup$
    – Jan
    Oct 17 '15 at 11:54

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