“…For details of the synthesis, see: Kaupang (2010); Toma et al (2007) and for the synthesis of related diazoacetamides, see: Kaupang et al (2010); Kaupang (2010); Ouihia et al (1993). For quantum chemical calculations involving the acetamide analogue of the title compound, see: Fraenkel et al (1992). For the Chemical Abstracts Service, see: American Chemical Society (2008).…”
In the molecule of the title compound, C6H9N3O3S, at 105 K, the six-membered ring is predominantly found in the chair conformation, with 1.89 (14)% in the boat conformation. In the crystal structure, there are five intermolecular C—H⋯O=C and C—H⋯O=S contacts less than 2.6 Å, as well as a weak C—H⋯N=N interaction to the diazo group.
“…For details of the synthesis, see: Kaupang (2010); Toma et al (2007) and for the synthesis of related diazoacetamides, see: Kaupang et al (2010); Kaupang (2010); Ouihia et al (1993). For quantum chemical calculations involving the acetamide analogue of the title compound, see: Fraenkel et al (1992). For the Chemical Abstracts Service, see: American Chemical Society (2008).…”
In the molecule of the title compound, C6H9N3O3S, at 105 K, the six-membered ring is predominantly found in the chair conformation, with 1.89 (14)% in the boat conformation. In the crystal structure, there are five intermolecular C—H⋯O=C and C—H⋯O=S contacts less than 2.6 Å, as well as a weak C—H⋯N=N interaction to the diazo group.
“…7 Recently, some experimental and theoretical works have dealt with the cycloconjugation effects of second-row elements on the b-sulfonylenamine moiety. 8 The aim of the present work was to study the differences between the two types of enamines as regards the influence of hydrogen bond formation on the measured and calculated NMR parameters. The experimental values and their variation were then used to monitor the presence and strength of intramolecular hydrogen bonds in the studied compounds, which are presented in Scheme 2.…”
A comparison of hydrogen bond strengths in various enamines was made by monitoring the differential shifts Dd(X) as the difference of NMR chemical shifts between E and Z forms of the nuclei directly involved in hydrogen bonding, i.e., X = 15 N, 1 H, 17 O atoms. The interpretation of these differential values was aided by ab initio calculations and X-ray derived geometric parameters for selected compounds. It is shown that Dd(N 1 H) and Dd( 15 N) give conclusive results and their changes are rationally interpreted by invoking established contributing effects that influence the values of chemical shifts. The Dd( 17 O) parameter is sensitive to intramolecular geometry, mainly bond angles around oxygen and co-planarity of the atoms forming the hydrogen bonds. The latter factor is important in determining the strength of hydrogen bonds. Even a weak acceptor such as the lactone function gives a relatively strong hydrogen bond as compared with sp 3 -hybridized sulfonyl or sulfinyl acceptors. The hybridization of the penultimate atom of an acceptor plays a crucial role in determining the strength of hydrogen bonding. P A P E R NJC www.rsc.org/njc 1562 N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 5 6 2 -1 5 6 7
“…At low temperatures, <180 K, unexpected nonequivalences seen among 13 C resonance in ion-paired allylic lithium compounds, for example, 3 , showed for the first time that coordinated TMEDA was unsymmetrically sited with respect to the allyl loop and that ion pairs have energetically favored structures. Then, signal-averaging effects observed with increasing temperature were shown to result from the dynamics of reorientation of coordinated lithium with respect to the anion within the ion pair. , …”
Several 1-sila allylic lithium compounds have been prepared with potential ligands for Li substituted
at the 2-position. They are [2-[[cis-2,5-bis(methoxymethyl)-1-pyrrolidinyl]methyl]-1-(trimethylsilyl)allyl]lithium
(22), [2-[[cis-2,5-bis(methoxymethyl)-1-pyrrolidinyl]methyl]-1-(dimethylethylsilyl)allyl]lithium (23), [2-[[bis(2-methoxyethyl)amino]methyl]-1-(dimethylethylsilyl)allyl]lithium (24), [2-[[bis(2-methoxyethyl)amino]methyl]-1-(tert-butyldimethylsilyl)allyl]lithium (25), and [2-[2-[bis(2-methoxyethyl)amino]-1,1-dimethylethyl](ethyldimethylsilyl)]allyllithium (26). Using diethyl ether or THF solutions all these compounds exhibited one bond
13C, 7Li spin coupling of ∼8 Hz, a 1:1:1:1 13C NMR pattern indicating monomeric structures; all show ligand
resonances to be magnetically nonequivalent and reveal C1, C3
13C NMR shifts of about 40 and 75 δ which
lie between those for model delocalized 1 and localized species 2. These compounds are concluded to be
examples of the heretofore missing folded, internally tridentately coordinated partially delocalized structures
with small detectable C, Li covalence. The exception is 25 which, in diethyl ether, consists of a rapidly
interconverting equilibrium mixture of localized and delocalized more solvated forms, the former prevailing
at 300 K and progressively converting mainly to the latter by 180 K. NMR line shape analysis of the
diastereotopic gem methylsilyl 13C resonances as well as that due to the ligand carbons shows that all these
line shape changes are due to the dynamics of inversion at lithium-bound carbon and that other ligand
reorientation processes are slower than carbanide inversion; for inversion, ΔH
⧧ is found to be 6−9 kcal·mol-1,
respectively. Averaging with increasing temperature of the 13C, 7Li spin coupling in 24 provides the dynamics
of bimolecular carbon lithium bond exchange with ΔH
⧧ of 12 kcal·mol-1. Mechanisms are proposed on the
basis of the data. We ascribe restricted stereochemistry of ligand lithium coordination to be responsible for
these unusual internally coordinated structures.
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