Dramatic effect of the nature of R on the intrinsic acidity and basicity of potential astrochemical R–C≡COH and R–C≡CSH compounds

• Published in: Theoretical chemistry accounts 2023, Vol.142 (3), Article 28
• Main Authors: Mó, Otilia, Alkorta, Ibon, Guillemin, Jean-Claude, Yáñez, Manuel
• Format: Article
• Language: English
• Subjects: Analogs; Atomic/Molecular Structure and Spectra; Basicity; Bonding strength; Chemical bonds; Chemical Sciences; Chemistry; Chemistry and Materials Science; Inorganic Chemistry; Mathematical analysis; Organic Chemistry; Physical Chemistry; Theoretical and Computational Chemistry
• ISSN: 1432-881X; 1432-2234
• DOI: 10.1007/s00214-023-02967-0

The effect of changing the nature of the R substituent from the first row (H, Li, BeH, BH 2 , CH 3 , NH 2 , OH and F) to second row (Na, MgH, AlH 2 , SiH 3 , PH 2 , SH and Cl) on the intrinsic acidity and basicity of R–C≡COH and R–C≡CSH compounds was investigated through the use of G4 high-level ab initio calculation. The variation of the acidity and basicity of the R–C≡CSH derivatives as a function of R is practically parallel to that found for the corresponding R–C≡COH analogs; though the basicities of the former are 9–14% higher than those of the latter, the acidity gap being very small (~ 2%). When this analysis is extended to the derivatives in which the triple CC bond is replaced by a double or single bond, it is found that the acidity gap increases systematically as the CC bond goes from triple to single; whereas, as expected for the basicity, the trend is the opposite. Quite surprisingly, however, the variation of the basicity of R–C≡CX (X = OH, SH) compounds with the nature of the first-row substituents, R, is remarkably different from that produced by the second-row analogs. The same is observed as far as intrinsic acidities are concerned. These dissimilarities reflect the rather different changes in the strength of the CC and the CX (X = OH, SH) bonds when a first-row substituent is replaced by the second-row analog, as reflected in the atoms in molecules (AIM), natural bond orbital (NBO) and the electron localization function (ELF) analyses of the corresponding species.