Data: Rotational Dynamic of Methylen-Group in Benzylic Derivatives: Intramolecular Non-covalent Bindings Driven Conformational Restriction

Herein we provided a general and consistent perspective of the rotational dynamic of methylene-group in benzylic derivatives from experimental and theoretical analysis. Different conformational states including the most stable conformation were recognized from DFT-calculations. Further calculations showed that the most stable conformation of the benzylic-amine and benzylic-alcohol compounds was defined by the existence of an intramolecular binding between the benzylic-amine substitution and ortho- substitution such as halogen, hydrogen or nucleophile-π binding. Neither type of intramolecular interaction was identified from benzyl-bromide compounds. Energetically, the rotational barrier of the methylene-group was increased as function of the nature of the ortho-substitution as follows: 2,6-dibrominated˃˃ 2-iodinated ~ 2-brominated˃ 2-arylated≥ 2,6-unsubstituted˃ 2-fluorinated. Experimentally, in solid-state, structural aspects such as the most preferred conformation state or intramoelcular binding were supported by X-ray studies. In solution, scalar correlations between the methylene-hydrogens with the vicinal ortho- or meta-protons from a simple 1H/1H-COSY measurement allowed us to confirm the most stable conformation for the studied benzylic compounds as well as to give a general draw about the rotational dynamic of the methylene-group in these benzylic compounds. From the benzyl-amines, the 2,6-dibrominated showed the strongest H-H correlations, followed by the 2-iodinated and 2-brominated compounds, whereas the 2-arylated, 2,6-unsubstituted and 2-fluorinated showed a discrete or null H-H correlations. All studied benzyl-bromides did not show H-H correlations. All these findings revealed that the rotation of the methylene-group is restricted by steric hindrance derived from ortho-substituent as well as by the existence of an intramolecular binding involving the benzyl-substituent, being this last the most determinant factor, although the co-existence of both factors restricted even more the free rotation of methylene-group.

The data include a detailed theoretical output concerning structure optimization, conformational analysis (scans), NBO calculations, X-ray data and NMR data for most of 40 compounds. Some figure and graphic, which are found in the manuscript and supporting Information material, can be found.