Archive for October, 2023

More examples of “double-headed” curly arrows: S and C Nucleophiles attacking acetyl chloride

Thursday, October 12th, 2023

In an earlier post on this topic,[1] I described how the curly-arrows describing the mechanism of a nucleophilic addition at a carbonyl group choreograph in two distinct ways, as seen in red or blue below. The arrows in red can be described as firstly addition to the carbonyl group to form either a transient intermediate (a two-step process) or instead a formal transition state state as a concerted single-step mechanism. The blue arrows do the reverse; firstly elimination and then followed by addition. I will use the shorthand AE for the first type and EA for the second type. Here I explore some more nucleophiles to see which of these two mechanisms they follow. Data for these results can be found at 10.14469/hpc/13171
N- carbon ylid: This is a very facile (low-barrier) reaction with a C-O bond length response that initially increases steeply, followed by a more modest decline and hence corresponds to an AE mechanism.



  1. H. Rzepa, "The “double-headed” curly arrow as used in mechanistic representations.", 2023.