Discovering the role of substrate in aldehyde hydrogenation

In this manuscript, we investigated in detail one of the critical parameters that govern the reactivity of the carbonylic group toward hydrogenation and hydrodeoxygenation: the effect of the side chains of aldehydes. We observed that the presence of a ?-electron conjugation on the side chains strongly affects the conversion of aldehydes to alcohols and hydrocarbons under the reaction conditions studied. In particular, the presence of a strong ?-electron conjugation, such as the aromatic ring, enables the hydrogenation and further hydrodeoxygenation of the carbonylic group, while, on the other hand, molecules with no or weak ?-electron conjugation (such as alkyl chains or single conjugated C[dbnd]C double bonds) remained inactive. These results were supported by adsorption analyses as well as theoretical models, which showed that differences in adsorption mode and strength between two model substrates (benzaldehyde and octanal) were not the decisive factors in the conversion of the carbonyl group.