## 4 Conclusions  
From the experimental data, new thermochemical and thermophysical properties were obtained for two methyl-indanones and two methoxy-indanones, namely the standard molar enthalpies of formation in the condensed and gaseous phases and the standard molar enthalpies of vaporization/sublimation. Complementarily, computational calculations at the G3(MP2)//B3 LYP level were carried out, and the estimated gas-phase enthalpies of formation of indanones studied compared very well with the experimental data. Thus, this methodology was used to estimate the value of the corresponding property for 2-methylcyclopentanone. The energetic effects associated with the presence of a methyl and a methoxy group in different positions of 1-indanone were analyzed and compared with an identical insertion in benzene and naphthalene. Thus, it can be assumed that the indanone cyclic system with these substituents positioned in several positions are almost energetically independent of the surrounding chemical environment. Similar studies should be enlarged to other structurally related compounds in order to establish more accurate structural-energy correlations for estimates of the same properties in compounds whose experimental study is not feasible. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app131810262/s1](https://www.mdpi.com/article/10.3390/app131810262/s1)]([https://www.mdpi.com/article/10.3390/app131810262/s1](https://www.mdpi.com/article/10.3390/app131810262/s1)), Tables S1-S4: data of all the combustion calorimetry experiments of indanones; Table S5: values of the standard molar heat capacities in the gaseous phase of indanones; Table S6: areas and transmission probability factors of the effusion orifics; Table S7: data of all the effusion experiments for 5-methoxy-1-indanone; Figure S1: molecular structures of the most stable conformation of 2-methyl-1-indanone, 3-methyl-1-indanone and 4-methoxy-1-indanone in the gaseous phase, optimized by B3 LYP/6-31G(d) level of theory; Table S8: conformational analysis of 5-methoxy-1-indanone; Tables S9-S12: working reactions for the estimation of the gas-phase enthalpy of formation of indanones; Table S13: working reactions for the estimation of the gas-phase enthalpy of formation of 2-methylcyclopentanone; Table S14: G3(MP2)//B3 LYP calculated absolute enthalpies, at T = 298.15 K, and experimental gas-phase values for all the molecules used. Figure 5: Strongest electronic interactions for 2 MI (more details in Table 9). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Electronic Interactions**} & \multirow{2}{*}{**Donor (i)**} & \multirow{2}{*}{**Acceptor (j)**} & \multicolumn{2}{c}{**E (k)-mol\({}^{-1}\))**} \\ \cline{3-5}  & & & **2 MI** & **3 MI** \\ \hline (1) & \(\pi(\text{C}_{4}-\text{C}_{5})\) & \(\pi^{\ast}(\text{C}_{8}-\text{C}_{9})\) & 95.1 & 95.2 \\ (2) & \(\pi(\text{C}_{4}-\text{C}_{5})\) & \(\pi^{\ast}(\text{C}_{6}-\text{C}_{7})\) & 71.2 & 71.2 \\ (3) & \(\pi(\text{C}_{6}-\text{C}_{7})\) & \(\pi^{\ast}(\text{C}_{8}-\text{C}_{9})\) & 77.5 & 77.6 \\ (4) & \(\pi(\text{C}_{6}-\text{C}_{7})\) & \(\pi^{\ast}(\text{C}_{4}-\text{C}_{5})\) & 90.3 & 90.0 \\ (5) & \(\pi^{\ast}(\text{C}_{1}-\text{O}_{10})\) & \(\pi^{\ast}(\text{C}_{8}-\text{C}_{9})\) & 589.1 & 544.4 \\ (6) & \(\pi^{\ast}(\text{C}_{4}-\text{C}_{5})\) & \(\pi^{\ast}(\text{C}_{8}-\text{C}_{9})\) & 1006.1 & 945.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Partial calculation results obtained for 2 MI and 3 MI molecules via NBO analysis. **Author Contributions:** Conceptualization, A.L.R.S. and M.D.M.C.R.d.S. ; Methodology, A.L.R.S. and M.D.M.C.R.d.S. ; Software, A.L.R.S. and M.D.M.C.R.d.S. ; Investigation, A.L.R.S. and G.P.L. ; Writing--original draft, A.L.R.S. and G.P.L. ; Writing--review & editing, A.L.R.S. and M.D.M.C.R.d.S. All authors have read and agreed to the published version of the manuscript.