S7I1+: The largest anomeric effect exhibited by sulfur.

In this series of posts about the electronic effects in small sulfur rings[cite]10.59350/rzepa.28615[/cite] I have explored increasingly large induced geometric effects. Here is the largest so far, for the compound S₇I¹⁺[cite]10.1021/ic50225a048[/cite]

The calculated geometry[cite]10.14469/hpc/15236[/cite] is shown below, with the crystallographic values in parentheses – the two matching very well.

The calculated NBO7 stereoelectronic analysis identifies an especially strong donor (S7) interaction with an acceptor S4-S7, the E(2) energy being 36.9 kcal/mol. The Wiberg S4-S5 bond index is 0.512 and the S-S stretching wavenumber is ν 131. The Wiberg index for S4-S7 is 1.4618 and the S-S stretch ν 667 cm^-1, matching the shortest bond.

The electronic overlap is shown below (click on image to view as a 3D model).

So we end with the current record for an S_Lp/SS_σ* interaction of 36.9 kcal/mol. Who would have thought that small sulfur rings could be such fun!

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This entry was posted on Wednesday, May 21st, 2025 at 9:48 am and is filed under Interesting chemistry, reaction mechanism. You can follow any responses to this entry through the RSS 2.0 feed.