Theoretical model of internal rotation in monosubstituted derivatives of furfural

Abstract

The present work explores the effect of substitution in all free positions of furfural on conformational preferences of formyl group by using ab-initio calculations at the MP2/6-31G(p,d) level of theory. Theoretical modeling was made in vacuo. The selected substituents were -CH(3), NH(2), NO(2) and F groups in 3, 4, 5 and ipso carbonyl positions. Geometries of all derivatives were analyzed and it is ascertained that substitution has not important consequences on furan ring geometry. Differences of energy between OO-cis and trans conformers and energy barriers between them are described and extreme cases are explained. Interesting features appear in the cases of -NH(2) and -NO(2) groups, and particularly when the 3 and ipso carbonyl positions are substituted. Variations in energy barriers are correlated with variations in C2-C6 distances for the transition states and planar forms. Substitution effect on Mülliken charges are analyzed and related with internal rotation energy barriers and differences between conformers.

Rotational barrier, energy difference and thermodynamic parameters of 2-furoylfluoride, its sulfur and selenium analogues in the gas and solution phases: A theoretical study

“…Fifthly, the transition state for the rotation of the -CFY group does not occur at right angle to the furan ring but deviates as follows: (i) 88.2°, 88.2°, 88.3°(DFT/B3LYP) and (ii) 88.2°, 88.6°, 88.3°(MP2) for Y = O, S and Se, respectively. These observations are in agreement for monosubstituted derivatives of furfural studied by Crespo-Otero et al [11], where deviation ranges from 1.0°to 1.5°. Apart from these, the computed structural parameters, namely bond length and bond angle, of the title compounds are in agreement with their parent carbonyls [29].…”

“…The basis set used for all atoms is 6-311++G(d,p). The syn-and anti-rotamers have been studied in C s symmetry, the transition state has also been modelled in C 1 symmetry and it involves the planes containing C 2 Y 5 F 11 Table 1 Optimized structural parameters of the rotamers of 2-furoylfluoride, its sulfur and selenium analogues obtained using DFT/B3LYP/6-311++G(d,p).…”

“…They also found that solvents can reverse conformational preference due to the syn-rotamer getting more stabilised with increasing polarity of the solvent. Crespo-Otero et al [11] used MP2/6-31G(d,p) to investigate the effect of conformational preferences of furfural by considering substituents in all the free positions of the furan ring. They related the energy difference between the rotamers and internal barrier of rotation with computed Mulliken charges on the different atoms.…”

“…In the gas phase, the anti-rotamer is more stable and a transition state can be envisioned for the interconversion of the syn-and anti-rotamers. Furfural has been the subject of various experimental [2][3][4][5] and theoretical [5][6][7][8][9][10][11][12] studies involving conformational analysis. In a previous communication [13], we have studied furfural, thiofurfural and selenofurfural using density functional method in the gas phase and in polar and non-polar solvents.…”

Photoisomerization and Photochemistry of Matrix-Isolated 3-Furaldehyde

“…[10][11][12][13][14][15][16][17][18][19][20] 3FA and 2FA have been found to exist in the gas phase, nematic and isotropic solutions, and neat liquid state, as a mixture of two planar conformers differing by rotation of the aldehyde group around the exocyclic C-C bond (cis and trans with respect to the ring oxygen atom; see Scheme 1). [21][22][23][24][25][26][27][28] For 2FA, the trans conformer was found to be the lowest energy form, with gas phase reported values for ∆E (cis-trans) ranging from 3.10 to 8.79 kJ mol -1 , [18][19][20][21][22][23][24][25][26][27] which implies a minimum expected population of the conformational ground state of 2FA at room temperature (RT) of ca. 80%.…”