I was checking the mechanism for the Lossen Rearrangement, when I came across the chemical reaction denoted as follows:

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I couldn't find any resource where this notation was talked about.

What do the three arrows stacked as follows mean? A possible example where this is applied in literature would be appreciated.

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    $\begingroup$ Multiple reactions (I came across this in some IChO papers, so not a canonical reference) $\endgroup$ Commented Sep 17, 2020 at 15:07
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    $\begingroup$ It indicates there are several reactions in between with different reaction conditions before you achieve the final product. @Aniruddha Deb says it simply (I thought you know better Safdar! :-)). $\endgroup$ Commented Sep 17, 2020 at 15:29

2 Answers 2


There is an explicit answer in section 3. Other Horizontal Arrows of prof. Santiago Alvarez' published work [1, p. 594]:

Alvarez — horizontal arrows
Finally, multiple arrows (7) are used as an ellipsis for several intermediate steps in a chemical reaction.

Analogously, Nature Research Chemical Structures Guide (PDF) suggests using stacked multiple arrows as the multistep synthesis/reaction arrows:

Please use each type of arrow below for the indicated purpose.

Nature Research — arrows


  1. Alvarez, S. Chemistry: A Panoply of Arrows. Angew. Chem. Int. Ed. 2012, 51 (3), 590–600. DOI: 10.1002/anie.201101767.
  2. Nature Research. Style Guide for Chemical Structures; 2021. Accessed 2021-06-03. (PDF)

It means that after multiple (unspecified) steps, the substrate on the left is transformed into the product on the right. It can be mechanistic steps or synthesis steps (to infer from the context).

Here is an example from the literature where the authors have added "steps" to make it perfectly clear. (Nicolaou, Kyriacos Costa, et al. "The Diels–Alder reaction in total synthesis." Angewandte Chemie International Edition 41.10 (2002): 1668-1698.)



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