Contribution to the Study of the Gauche Effect. The Complete Structure of the Anti Rotamer of 1,2-Difluoroethane

Applications of the Quantum Theory of Atoms in Molecules in Organic Chemistry – Charge Distribution, Conformational Analysis and Molecular Interactions

“…14.3.1.2 Rotational Barrier of 1,2-Disubstituted Ethanes This subsection presents results from a study of the conformational behavior of the molecules XCH 2 CH 2 X, where X ¼ CH3; Cl, or F. It has been shown exper- Angle imentally that whereas the antiperiplanar (app) conformation is the most stable for the conformers of both butane [20] and 1,2-dichloroethane [29], the gauche (sc) conformation is the most stable for 1,2-difluoroethane [29], a behavior known as the gauche effect [30]. The highest of the rotational barriers of butane occurs when the two methyl groups eclipse each other and has been attributed to the action of van der Waals repulsion between them.…”

Synthesis and structural characterization of metal complexes based on pyrazole/imidazolium chlorides

“…Our preliminarily investigation shows that catalysts 3a-3d, in regardless of the N-substitutions, are equally effective in the production of trans n-butyl cinnamate quantitatively in 6 h (entries 1-4). To gauge the effectiveness of 3a-3d in comparison with simple phosphine-based catalytic systems of Pd(OAc) 2 /2PPh 3 and Pd(PPh 3 ) 4 , we carried out the standard catalytic reaction with the latter two systems under identical conditions (entries [5][6]. The results clearly indicate that 3a-3d and the phosphine-based systems are equally effective.…”

“…Most importantly, the ethylene spacer in L has a high preference to adopt the less stable gauche conformation as revealed by X-ray structural analysis. The anomalous gauche effect in 1,2-difluoroethane, with the gauche rotamer being more stable than its anti rotamer, has been widely reported and can be attributed to a stereo-electronic nature [5]. Alternatively, the energetic gauche rotamer can be stabilized by intermolecular forces such as hydrogen bonds in the crystal lattice [6].…”

Methyl 6-deoxy-6-iodo-α-d-glucopyranoside: crystal structure and high-resolution NMR spectroscopy

“…21,22 The stability of the gg conformation in the case of the hydroxymethyl group may also be due to the 'gauche effect'. 23 This requires the hydrogen atom to be oriented antiperiplanarly to the electronegative atoms (F and O). The stability of the gg conformation in the case of the iodomethyl group cannot be explained either by O-HÁÁÁI interactions, which are not detected (Table 4), or by the 'gauche effect', because the electronegativity of the iodine atom is relatively small.…”