A low energy barrier for rotation around carbon—carbon double bond

Shvo, Youval; Taylor, Keenan C.; Bartulin, J.

doi:10.1016/s0040-4039(01)89865-8

Cited by 47 publications

(15 citation statements)

References 5 publications

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“…Despite wide use in organic synthesis, the study of the physical and physicochemical properties of these compounds has been mainly carried out by NMR and UV spectroscopy, where only basic NMR characteristics (chemical shift, coupling constants) and UV maxima were measured [11][12][13][14][15][16]. Therefore, we decided to study these compounds by vibrational spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

The vibrational and NMR spectra, conformations and ab initio calculations of aminomethylene, propanedinitrile and itsN-methyl derivatives

et al. 1996

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The IR and Raman spectra of aminomethylene propanedinitrile (AM) [H2N--CH=C(CN)2], (methylamino)methylene propanedinitrile (MAM) [CHaNH--CH=C(CN)2] and (dimethylamino)methylene propanedinitrile (DMAM) [(CH3)2N--CH=C(CN)2] as solids and solutes in various solvents have been recorded in the region 4000-50 cm-~. AM and DMAM can exist only as one conformer. From the vibrational and NMR spectra of MAM in solutions, the existence of two conformers with the methyl grotip oriented anti and syn toward the double C-----C bond were confirmed. The enthalpy difference AH ~ between the conformers was measured to be 3.7 + 1.4 kJ mol -l from the IR spectra in acetonitrile solution and 3.4 + 1.1 kJ mol -I from the NMR spectra in DMSO solution. Semiempirical (AM1, PM3, MNDO, MINDO3) and ab initio SCF calculations using a DZP basis set were carried out for all three compounds. The calculations support the existence of two conformers anti and syn for MAM, with anti being 7.8 kJ mol -~ more stable than syn from ab initio and 8.6, 13.4, 11.6, and 10.8 kJ mol -~ from AM1, PM3, MNDO, and MINDO3 calculations, respectively. Finally, complete assignments of the vibrational spectra for all three compounds were made with the aid of normal coordinate calculations employing scaled ab initio force constants. The same scale factors were optimized on the experimental frequencies of all three compounds, and a very good agreement between calculated and experimental frequencies was achieved.KEY WORDS: Vibrational and NMR spectra; conformational analysis; enamines; semiempirical and ab initio calculations.

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Section: Introductionmentioning

confidence: 99%

The vibrational and NMR spectra, conformations and ab initio calculations of aminomethylene, propanedinitrile and itsN-methyl derivatives

et al. 1996

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“…The choice of the reaction path ( A or B) is likely to depend on the ratio of two activation energies: (i) that of the rotation of the OR-2, and (ii) the OR-E -, OR-Z isomerization. Usually the activation energy of cis-trans isomerization is much higher than the barriers to rotation around single bonds but the situation may be reverse if the formal double bond is strongly polarized (7)(8)(9) where Co = the total initial concentration; 11, = integration data for the newly formed isomer; hz = integration data for the other isomer.…”

Section: Resultsmentioning

confidence: 99%

Kinetics of Z–E isomerization of spiroindolinopyrans

Gruda¹,

Leblanc²,

Sochanski³

1978

Can. J. Chem.

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The kinetics of the Z–E isomerization of a series of 3′-nonsymmetrically substituted spiroindolinopyrans bas been studied by nmr in different solvents.The rate-determining step in nonpolar solvents was found to be the cleavage of the C—O bond whereas in polar solvents it was the C(2)—C(3) bond rotation.A strong steric hindrance of substituents at carbon 3 was observed. It was found that the rate of the isomerization is more sensitive to the bulkiness of the substituent at C(3′) than at the N(1′). Protic solvents enhance the reaction more than nonprotic polar solvents.

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“…Here it was chosen to give the maximum experimental and calculated intensity the same value. With the usual abbreviation cc, = T2\-I -27;i(vAv) and assuming slow passage conditions, linear equations (I) to (8) in the complex magnetic moments GA to Glf of sites A to H are obtained. (pl.…”

Section: E X P E R I M E N T a Lmentioning

confidence: 99%

Studies of polarised ethylenes—IV: Barriers to rotation around formal double bonds and formal single bonds in 1, 1‐bis‐dimethylaminoethylenes

Wennerbeck

Sandström

1972

Org. Magn. Reson.

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1 .l-Bis-dimethylaminoethylenes with electron attracting substituents on C , show rotations around the C-=C and C-N bonds, the rates of which are in most cases measurable by the N M R line shape method. The temperature-dependent four-and eight-site N M R spectra have been analysed and the barricrs to rotation around the different bonds have been evaluated by a complete line shape treatment based on the Bloch formalism. Assignment of sites to methyl groups has been made with the aid of aromatic solvent induced shifts and anisotropy effects.

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A low energy barrier for rotation around carbon—carbon double bond

Cited by 47 publications

References 5 publications

The vibrational and NMR spectra, conformations and ab initio calculations of aminomethylene, propanedinitrile and itsN-methyl derivatives

The vibrational and NMR spectra, conformations and ab initio calculations of aminomethylene, propanedinitrile and itsN-methyl derivatives

Kinetics of Z–E isomerization of spiroindolinopyrans

Studies of polarised ethylenes—IV: Barriers to rotation around formal double bonds and formal single bonds in 1, 1‐bis‐dimethylaminoethylenes

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