**4. Conclusions**

Ab initio MP2/aug'-cc-pVTZ calculations were carried out to identify and characterize hydrogen-bonded equilibrium structures and transition structures on the 1-oxo-3-hydroxy-2-propene:acid (**1**:acid) potential energy surfaces, with the acids LiH, LiF, BeH2, and BeF2. The results of these calculations support the following statements:


5. EOM-CCSD spin–spin coupling constants 2hJ(O–O), 1hJ(H–O), and 1J(O–H) were computed for all equilibrium and transition structures. Plots of 2hJ(O–O) versus the O–O distance, 1hJ(H–O) versus the H–O distance across the hydrogen bond, and 1J(O–H) versus the covalent O–H bond distance of **1** exhibit a second-order dependence of the coupling constant on the corresponding distance, with very high correlation coefficients.

**Supplementary Materials:** The following are available online, Table S1: Structures (Å), total energies (au), and molecular graphs of 1-oxo-3-hydroxy-2-propene:acid complexes; Figure S1: Relationship between electron densities at the O–H hydrogen bonds and interatomic distances; Table S2: Components of spin–spin coupling constants 2hJ(O–O), 1hJ(H–O), and 1J(O–H) (Hz).

**Author Contributions:** I.A. and J.E.D.B. carried out the calculations. J.E.D.B., J.E., and I.A. contributed equally to the writing of this paper. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was carried out with financial support from the Ministerio de Ciencia, Innovación y Universidades of Spain (Project No. PGC2018–094644-B-C22) and Comunidad Autónoma de Madrid (P2018/EMT–4329 AIRTEC-CM).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available in the article and in the Supplementary Material.

**Conflicts of Interest:** The authors declare no conflict of interest.

**Sample Availability:** Not applicable.
