## 3 Results
### Gas-Phase Enthalpies of Formation of Indanones
Figure 3 shows the enthalpic increments resulting from the insertion of a methoxy group into benzene, anthracene and 1-indanone. The values obtained exhibit good agree \begin{table}
\begin{tabular}{c c c c} \hline
**Compound** & **\(\Delta_{\rm f}\,H_{\rm m}^{\rm c}(\rm c\rm\rm\bf r\), l/k\(\cdot\)mol\({}^{-1}\)** & \(\Delta_{\rm c_{\rm f}\,H_{\rm m}^{\rm c}(\rm g)\)}^{\rm g}\)** & \(\Delta_{\rm f}\,H_{\rm m}^{\rm c}(\rm\rm\bf g)\)**/k\(\cdot\)mol\({}^{-1}\)** & \(\Delta_{\rm f}\,H_{\rm m}^{\rm c}(\rm\bf g)\)**/k\(\cdot\)mol\({}^{-1}\)** \\ \hline
2 MI & \(-170.4\pm 2.9\) & \(65.0\pm 1.8\) & \(-105.4\pm 3.5\) \\
3 MI & \(-157.0\pm 3.0\) & \(64.1\pm 1.8\) & \(-92.9\pm 3.5\) \\
4 MI & \(-315.9\pm 2.4\) & \(98.3\pm 2.4\) & \(-217.6\pm 3.4\) \\
5 MI & \(-317.0\pm 2.1\) & \(29.4\pm 3.1\) & \({}^{b}\) \\  & & & \(101.4\pm 0.3\) & \({}^{c}\) \\ \hline \end{tabular} \({}^{a}\) Uncertainties calculated through the RSS method; \({}^{b}\) Calvet microcalorimetry system; \({}^{c}\) Knudsen effusion (KE) method; \({}^{d}\) value obtained using the sublimation enthalpy derived from the KE method.  
\end{table} 
Table 7: Derived standard (\(p^{o}\) = 0.1 MPa) molar enthalpies of formation in the gaseous phase, at \(T\) = 28.15 K, for the compounds studied \({}^{a}\). \begin{table}
\begin{tabular}{c c c c} \hline
**Compound** & **Experimental Value** & \multicolumn{2}{c}{**Computed G3(MP2)/B3 LYP**} \\  & & **Gas-Phase Enthalpies of Formation** & \(\Delta\)\({}^{a}\) \\ \hline
2 MI & \(-105.4\pm 3.5\) & \(-94.4\pm 4.2\) & \(+10.2\) \\
3 MI & \(-92.9\pm 3.5\) & \(-94.3\pm 4.2\) & \(-1.4\) \\
4 MI & \(-217.6\pm 3.4\) & \(-219.1\pm 3.3\) & \(-1.5\) \\
5 MI & \(-215.6\pm 2.1\) & \(-220.3\pm 3.3\) & \(-4.7\) \\ \hline \end{tabular} \({}^{a}\) Enthalpic differences between the computed and experimental values.  
\end{table} 
Table 8: Comparison between the experimental and computed G3(MP2)//B3 LYP gas-phase enthalpies of formation, in kJ\(\cdot\)mol\({}^{-1}\), of the indanones studied in this work, at \(T\) = 298.15 K \({}^{a}\). ment, indicating that the energy contribution to the enthalpy of formation in the gas phase due to the insertion of this functional group in aromatic cyclic systems, as well as in positions 4, 5 and 6 of the 1-indanone, is equivalent. In addition, the electron-donating nature of this functional group confers a stabilizing effect on each compound in comparison with the molecular core. Similarly, the enthalpic increments associated with the presence of the methyl group at positions 2 and 3 of both 1-indanone and cyclopentanone are presented in Figure 4. These values are in good agreement, indicating that the energetic effect of the methyl group on these cyclic systems is almost independent of the surrounding chemical environment. Figure 3: Enthalpic increments (all values in kJ\(\cdot\)mol\({}^{-1}\)) for the insertion of a methoxy group in benzene, anthracene and 1-indanone. \({}^{a}\) Benzene [32]. \({}^{b}\) Anthracene [33]. \({}^{c}\) 1-methoxynaphthalene [31]. \({}^{d}\) 1-indanone [11]. \({}^{e}\) This work. \({}^{f}\)6-methoxy-1-indanone [10]. Following an extensive literature review, no experimental or computational data for the 2-methylcyclopentanone were found. Therefore, the standard molar enthalpy of formation has been estimated using the G3(MP2)//B3 LYP computational method, obtaining \(\left\langle\Delta_{\mathrm{f}}H_{\mathrm{m}}^{{}^{\prime\prime}}\right\rangle = -(226.7\pm 2.4)\) kJ\(\cdot\)mol\({}^{-1}\). Details of this calculation are in the Supporting Information (Table S13). Finally, a quantitative analysis of the effects of the delocalization of the electron density on 2 MI and 3 MI was performed, using NBO calculations at the B3 LYP/6-311+G(2 df,2p) level of theory, seeking a possible contribution on the difference between the experimental \(\Delta_{\mathrm{f}}\)\(H_{\mathrm{m}}^{{}^{\prime\prime}}(\mathrm{g})\) values.