Thermal isomerization about double bonds

Kessler, Horst

doi:10.1016/s0040-4020(01)97319-3

Cited by 81 publications

(22 citation statements)

References 91 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Alternatively, it could be that the rate of E/Z isomerization is simply too fast and the coalescence temperature lies well below 95°C, or a combination of both of these factors. Another possibility is that all pairs of exchanging spins are isochronous, or effectively so, but this is simply discounted as being too improbable when observing both 13 C and 1 H at medium field strengths. From preliminary calculations of the heat of formation versus angle of rotation about the C 9 -N 1 0 single bond using semiempirical methods for both the E and Z configurations for both 1 and 2, energy minima were obtained for angles of ca 90°for in all cases, consistent with the observed equivalence of the υ values for the corresponding protons and carbons of the two acridine side rings in the NMR spectra.…”

Section: Determination Of Configurationmentioning

confidence: 99%

“…5a Is it because the system is overly biased, the interconversion rate too fast or a combination of both of these factors? Another possibility is that all pairs of exchanging spins are isochronous, or effectively so, but this is simply discounted as being too improbable when observing both 13 C and 1 H at medium field strengths.…”

Section: Introductionmentioning

confidence: 99%

“…4b Various mechanisms exist for the E/Z isomerization of a C N double bond such as protonation, 9,12a,13 nucleophilic catalysis, 9,12a,13 photolysis, 14 N-inversion, 4,5b,5c,6,9,13,15 rotation, 4,6,9,13,15 dissociation-recombination 13 and tautomerization. 13 In the absence of appropriate conditions for the systems under study here, the first three mechanisms are neglected. Similarly, the last two mechanisms are limited to special cases and are also not relevant to this study.…”

Section: Introductionmentioning

confidence: 99%

“…4,5b,5c,6,13,15 Generally, for imines and related compounds, N-inversion is considered to be the sole dominating mechanism, 13 although calculations have even predicted rotation to be preferred in certain cases. 16 In particular, N-inversion has been decisively declared to be the sole mechanism in effect for the iminocarbonates 4b,5b,5c, 6 and iminodithiocarbonates.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Configuration andE/Zinterconversion mechanism ofO(S)-allyl-S(O)-methyl-N-(acridin-9-yl) iminothiocarbonate

et al. 2005

View full text Add to dashboard Cite

The configuration and dynamic behavior of O-allyl-S-methyl-N-(acridin-9-yl)iminothiocarbonate (1) and its S-allyl-O-methyl regioisomer (2) were studied using quantum chemical calculations and by applying a novel graphical method to scatter maps obtained from MD simulations for evaluation of an NOE-weighted internuclear distance (r(NOE)). Energy calculations indicated that the Z configuration was predominant for each compound and, further, this was supported both by the calculated chemical shifts and the r(NOE). Both N-inversion- and rotation-type transition-state structures were also calculated for the E/Z isomerization process, the results indicating that the preferred interconversion mechanism for 1 is N-inversion, but contrastingly, interconversion via rotation is equally as probable as N-inversion for 2. This supports the notion that one or the other or both pathways can be active and each system needs to be assessed on a case-by-case basis.

show abstract

Section: Determination Of Configurationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Configuration andE/Zinterconversion mechanism ofO(S)-allyl-S(O)-methyl-N-(acridin-9-yl) iminothiocarbonate

et al. 2005

View full text Add to dashboard Cite

show abstract

“…In the first, the transition state has the structure 6, and the process may be termed "linear inversion" (18). In the second, the transition state has the structure 7, and the process is one of torsion along the C-X bond.…”

Section: Geometrieollsomerization Of 6h20hand Ch$h Scf Computationsmentioning

confidence: 99%

On the π-Donating Abilities of Sulfur and Oxygen. A Comparative Quantum Chemical Investigation of the Static and Dynamic Properties and Gas Phase Acidities of and

Bernardi¹,

Csizmadia²,

Schlegel³

et al. 1975

Can. J. Chem.

View full text Add to dashboard Cite

Chem. 53, 1144Chem. 53, (1975. Nonempirical SCF-MO computations have been performed on CH20, CH2S, and their t protonated derivatives CH20H and EH,SH. The methylene group of CH,O is strongly positive and that of CH2S is slightly negative, because oxygen in CH,O behaves towards carbon as a n-donor and o-acceptor, but sulfur in CH,S behaves as both a n-and a-donor. The total n-overlap in CH,O is greater th_an that in C+S.The stable conformations of CH,OH and CH,SH correspond in each case to a structure in which all atoms lie in the same plane. In this conformation, both the C-0 and C S bond lengths are substantially shorter than those of methanol and methanethiol, indicative of conjugative interaction between the cationic center and the adjacent heteroatom. From the results of a Mulliken-type population analysis it is found that, relative to hydrogen, OH and SH behave + towards an ad'acent CH2 group as electron-withdrawing and electron-releasing ligands, respec-2 + tively. When CH,OH is considered to form from CHI and OH fragments, n-donation from 0 to C amounts to 0.38 electron, but o-donation in the opposite direction amounts to 0.35 electron; the n-overlap population is 0.1496. A similar analysis of CH,SH reveals n-and o-donation from S to C of 0.53 and 0.15 electron, respectively, and a n-overlap population of 0.1734, so that suIfur forms a stronger n-bond to ,the aojacent cationic center.Geometrical isomerization of ~H , O H proceeds by linear inversion at oxygen, with a barrier of 13.98 kcal/mol; but that ~~E H , s H proceeds by rotationabout the C-S bond, with a barrier of 36.47 kcal/mol. This latter value is substantially higher than that (23 kcal/mol) computed for &H,OH with a rigid rotor model, and reflects the greater strength of the n-bond between sulfur and the adjacent cationic center.

show abstract

Rearrangements in amidines and related compounds

Михайлов

1991

PATAI'S Chemistry of Functional Groups

View full text Add to dashboard Cite

Thermal isomerization about double bonds

Cited by 81 publications

References 91 publications

Configuration andE/Zinterconversion mechanism ofO(S)-allyl-S(O)-methyl-N-(acridin-9-yl) iminothiocarbonate

Configuration andE/Zinterconversion mechanism ofO(S)-allyl-S(O)-methyl-N-(acridin-9-yl) iminothiocarbonate

On the π-Donating Abilities of Sulfur and Oxygen. A Comparative Quantum Chemical Investigation of the Static and Dynamic Properties and Gas Phase Acidities of and

Rearrangements in amidines and related compounds

Contact Info

Product

Resources

About