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Comparative Infra-Red, Raman, and Natural Bond Orbital Analyses of King's Sultam

Contributors

Hagemann, Hans-Rudolf; Dulak, Marcin; Chapuis, Christian; Wesolowski, Tomasz Adam; Jurczak, Janusz

Published in

Helvetica chimica acta, vol. 87, no. 7, p. 1748-1766

Publication date

2004

Abstract

By means of [1]H-NOESY- and Raman-spectroscopic analyses, we experimentally demonstrated the presence of the equatorial N—Me conformer of King's sultam 4b in solution, resulting from a rapid equilibrium. As a consequence, the value of the N lone-pair anomeric stabilization should be revised to 1.5-1.6 kcal/mol. Independently from the N tilting, natural bond orbital (NBO)-comparative analyses suggest that the S d* orbitals do not appear as primordial and stereospecific acceptors for the N lone pair. Second, the five-membered-ring sultams do not seem to be particularly well-stabilized by the S—C[sigma]* orbital in the N-substituted pseudo-axial conformation, as opposed to an idealized anti-periplanar situation for the six-membered-ring analogues. In this latter case, the other anti-periplanar C—C[sigma]* and C(1')—H/C(2')[sigma]* orbitals are as important, if not more, when compared to the S—C[sigma]* participation. In the pseudo-equatorial conformation,[upsilon]-sultams particularly benefit from the N lone-pair hyperconjugation with the anti-periplanar S—O[1][sigma]* and C(2)—H/C or C(1')—H/C[sigma]* orbitals. This is also the case for -sultams when the steric requirement of the N-substituent exceeds 1.6 kcal/mol. When both axial and equatorial conformations are sterically too exacting, the N-atom is prone to sp[2] hybridization or/and conformational changes (i.e., 12c). In that case also, the mode of stereoelectronic stabilization differs from [upsilon]- to [delta]-sultams.

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Citation (ISO format)

HAGEMANN, Hans-Rudolf et al. Comparative Infra-Red, Raman, and Natural Bond Orbital Analyses of King’s Sultam. In: Helvetica chimica acta, 2004, vol. 87, n° 7, p. 1748–1766. doi: 10.1002/hlca.200490158

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Journal ISSN

0018-019X
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Technical informations

Creation

02/10/2009 15:17:39

First validation

02/10/2009 15:17:39

Update

14/03/2023 15:15:07

Status update

14/03/2023 15:15:07

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