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

Abstract

The effect of changing the nature of the R substituent from the first row (H, Li, BeH, BH2, CH3, NH2, OH and F) to second row (Na, MgH, AlH2, SiH3, PH2, 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.

Preparation of Acetylenediol (HOCCOH) and Glyoxal (HCOCHO) in Interstellar Analog Ices of Carbon Monoxide and Water

“…Since the first identification of vinyl alcohol (CH 2 CHOH) in the interstellar medium (ISM) by Turner et al (Turner & Apponi 2001) two decades ago toward the dense molecular cloud Sagittarius B2(N), enols-alkenes carrying a hydroxyl group at a carbon-carbon double bond-have received considerable attention from the astrochemistry (Abplanalp et al 2016b;, synthetic organic chemistry (Mardyukov et al 2021(Mardyukov et al , 2023, physical chemistry (Taatjes et al 2005;Rösch et al 2021;Melosso et al 2022), and theoretical chemistry (Elango et al 2010;Ballotta et al 2023;Mó et al 2023;Würmel & Simmie 2024) communities. This interest is mainly due to their key role as reactive intermediates in the synthesis of biorelevant molecules related to the Origins of Life.…”