Zur Struktur und innermolekularen Beweglichkeit von 1,3‐Diazabutadienen

Michalik, Manfred; Evers, R.

doi:10.1002/zfch.19820221112

Cited by 2 publications

(1 citation statement)

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“…Both the barrier to rotation (Δ G ⧧ ) about the double bond and the chemical shift difference (Δδ C  C ) of the two sp 2 -hybridized carbons constituting the double bond have been employed to quantify the push − pull effect . If the compounds compared are rather similar, e.g., aroylcyanoketene S , S -acetals with varying substitution on the phenyl ring, then Δ G ⧧ and Δδ C  C can be linearly correlated 3 and Δδ C  C can even be satisfactorily employed as a substitute for Δ G ⧧ in cases where Δ G ⧧ cannot be determined, for example, either because it lies outside the bounds set by the NMR time scale , or because it forms part of a ring. , The push − pull effect has been satisfactorily assessed by both these parameters in various classes of compounds including push−pull alkenes, − push−pull butadienes, nitroenamines, 1-methyl-4-(2‘-methylthiovinyl)pyridinium iodide, and push−pull enynes . Other parameters that have been used to describe the push − pull effect include both the bond length and the π-bond order of the central CC partial double bond.…”

Section: Introductionmentioning

confidence: 99%

Electronic State of Push−Pull Alkenes: An Experimental Dynamic NMR and Theoretical ab Initio MO Study

2004

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The (1)H and (13)C NMR spectra of a number of push-pull alkenes were recorded and the (13)C chemical shifts calculated employing the GIAO perturbation method. Of the various levels of theory tried, MP2 calculations with a triple-zeta-valence basis set were found to be the most effective for providing reliable results. The effect of the solvent was also considered but only by single-point calculations. Generally, the agreement between the experimental and theoretically calculated (13)C chemical shifts was good with only the carbons of the carbonyl, thiocarbonyl, and cyano groups deviating significantly. The substituents on the different sides of the central C=C partial double bond were classified qualitatively with respect to their donor (S,S < S,N < N,N) and acceptor properties (C identical with N < C=O < C=S) and according to the ring size on the donor side (6 < 7 < 5). The geometries of both the ground (GS) and transition states (TS) of the restricted rotation about the central C=C partial double bond were also calculated at the HF and MP2 levels of theory and the free energy differences compared with the barriers to rotation determined experimentally by dynamic NMR spectroscopy. Structural differences between the various push-pull alkenes were reproduced well, but the barriers to rotation were generally overestimated theoretically. Nevertheless, by correlating the barriers to rotation and the length of the central C=C partial double bonds, the push-pull alkenes could be classified with respect to the amount of hydrogen bonding present, the extent of donor-acceptor interactions (the push-pull effect), and the level of steric hindrance within the molecules. Finally, by means of NBO analysis of a set of model push-pull alkenes (acceptors: -C identical with N, -CH=O, and -CH=S; donors: S, O, and NH), the occupation numbers of the bonding pi orbitals of the central C=C partial double bond were shown to quantitatively describe the acceptor powers of the substituents and the corresponding occupation numbers of the antibonding pi orbital the donor powers of the substituents. Thus, for the first time an estimation of both the acceptor and the donor properties of the substituents attached to the push-pull double bond have been separately quantified. Furthermore, both the balance between strong donor/weak acceptor substituents (and vice versa) and the additional influences on the barriers to rotation (hydrogen bonding and steric hindrance in the GSs and TSs) could be differentiated.

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Section: Introductionmentioning

confidence: 99%

Electronic State of Push−Pull Alkenes: An Experimental Dynamic NMR and Theoretical ab Initio MO Study

2004

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¹H‐NMR‐spektroskopische Untersuchungen an substituierten Crotonsäure‐ und Dithiocrotonsäureestern

Michalik

Kreutzmann

1983

J. Prakt. Chem.

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Zur Struktur und innermolekularen Beweglichkeit von 1,3‐Diazabutadienen

Cited by 2 publications

References 8 publications

Electronic State of Push−Pull Alkenes: An Experimental Dynamic NMR and Theoretical ab Initio MO Study

Electronic State of Push−Pull Alkenes: An Experimental Dynamic NMR and Theoretical ab Initio MO Study

¹H‐NMR‐spektroskopische Untersuchungen an substituierten Crotonsäure‐ und Dithiocrotonsäureestern

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Zur Struktur und innermolekularen Beweglichkeit von 1,3‐Diazabutadienen

Cited by 2 publications

References 8 publications

Electronic State of Push−Pull Alkenes: An Experimental Dynamic NMR and Theoretical ab Initio MO Study

Electronic State of Push−Pull Alkenes: An Experimental Dynamic NMR and Theoretical ab Initio MO Study

1H‐NMR‐spektroskopische Untersuchungen an substituierten Crotonsäure‐ und Dithiocrotonsäureestern

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¹H‐NMR‐spektroskopische Untersuchungen an substituierten Crotonsäure‐ und Dithiocrotonsäureestern