# Aromatic Amines in Organic Synthesis Part III; \(p\)-Aminocinnamic Acids and Their Methyl Esters
## 2 Results and Discussion
**} & \multirow{2}{*}{**Solvent**} & \multirow{2}{*}{\(\mathbf{\lambda_{\text{max abs}}}\)} & \multirow{2}{*}{\(\mathbf{\lambda_{\text{max dl}}}\)} & \multirow{2}{*}{\(\mathbf{\lambda_{\text{var}}}\)} & \multirow{2}{*}{\(\mathbf{\phi_{\text{fl}}}\)} & \(\mathbf{\tau_{1}^{\text{fl}}}\) & \(\mathbf{\tau_{2}^{\text{fl}}}\) & \multirow{2}{*}{\(\mathbf{\tau_{\text{av}}^{\text{fl}}}\)} & \multirow{2}{*}{\(\mathbf{\chi^{2}}\)} & \multirow{2}{*}{\(\mathbf{k_{\text{r}}}\)} & \multirow{2}{*}{\(\mathbf{k_{\text{nr}}}\)} & \multirow{2}{*}{\(\mathbf{k_{\text{rf}}}\)/\(\mathbf{k_{\text{nr}}}\)} & \multirow{2}{*}{\(\mathbf{f_{\text{os}}}\)} \\  & & \(\mathbf{\epsilon_{\text{max}}}\) & & & & & & & & & & & \\ \hline \multirow{2}{*}{2a} & \multirow{2}{*}{1,4-Dx} & 353 & \multirow{2}{*}{414} & \multirow{2}{*}{4174} & \multirow{2}{*}{0.84} & 0.074 & 0.521 & \multirow{2}{*}{0.08} & \multirow{2}{*}{2.194} & \multirow{2}{*}{1.07} & \multirow{2}{*}{12.6} & \multirow{2}{*}{0.0085} & \multirow{2}{*}{0.619} \\  & & 27.4 & & & & & & & & & & & & \\  & & 355 & \multirow{2}{*}{426} & \multirow{2}{*}{4695} & \multirow{2}{*}{0.61} & \multirow{2}{*}{0.88} & 0.896 & \multirow{2}{*}{0.09} & \multirow{2}{*}{2.419} & \multirow{2}{*}{0.673} & \multirow{2}{*}{11.0} & \multirow{2}{*}{0.0061} & \multirow{2}{*}{0.625} \\  & & 28.9 & & & & & & & & & & & \\  & 357 & \multirow{2}{*}{448} & \multirow{2}{*}{5690} & \multirow{2}{*}{2.06} & \multirow{2}{*}{99.48} & \multirow{2}{*}{0.52} & \multirow{2}{*}{0.14} & \multirow{2}{*}{1.700} & \multirow{2}{*}{1.48} & \multirow{2}{*}{7.04} & \multirow{2}{*}{0.021} & \multirow{2}{*}{0.646} \\  & DMF & 27.4 & & & & & & & & & & & \\  & 366 & \multirow{2}{*}{450} & \multirow{2}{*}{5100} & \multirow{2}{*}{59.9} & \multirow{2}{*}{67.07} & \multirow{2}{*}{32.93} & \multirow{2}{*}{1.95} & \multirow{2}{*}{1.096} & \multirow{2}{*}{3.06} & \multirow{2}{*}{0.205} & \multirow{2}{*}{1.49} & \multirow{2}{*}{0.466} \\  & & 20.9 & & & & & & & & & & & \\  & 370 & \multirow{2}{*}{471} & \multirow{2}{*}{5796} & \multirow{2}{*}{73.8} & \multirow{2}{*}{1.777} & \multirow{2}{*}{2.454} & \multirow{2}{*}{2.09} & \multirow{2}{*}{1.002} & \multirow{2}{*}{3.52} & \multirow{2}{*}{0.125} & \multirow{2}{*}{2.82} & \multirow{2}{*}{0.401} \\  & & 17.2 & &with a dimethylamine group. In the case of derivatives substituted into position 1, the intensity is much lower and does not exceed several percent [48; 49]. According to [PERSON] et al. [49] and [PERSON] et al. [48] the structure of the compounds based on 2-substituted naphthalene is flattened with a low torsion angle for C-NMe\({}_{2}\) due to the lack of unbonded interaction with the H8 hydrogen atom. In the case of 1-dialkylamino-substituted naphthalene, the optimized conformation of the amino group corresponds to a structure having a twisted lone pair orbital relative to the carbon 2p\(\pi\) orbital in the naphthalene ring. The lack of repulsion between the alkyl substituents on the nitrogen atom and the perihydrogen atom in the naphthalene ring counteracts the rotation of the amino group to the plane of the naphthalene ring, while simultaneously shifting the charge from the alkylamino group towards the electron-withdrawing substituent, which results in a redshift of the 2o absorption band. This is consistent with the MO calculation results [46]. Figure S19 shows the calculated molecular structure and electron distribution of the HOMO and LUMO energy levels of the 2a and 2o acids. A comparison of the electron distribution in the frontier molecular orbitals (MOs) reveals that HOMO-LUMO excitation moved the electron distribution from the dimethylamine group towards the withdrawing substituent via the aromatic \(\pi\) system, indicating a strong migration of the intramolecular charge transfer character of the acids. The HOMO and LUMO energies for compound 2a were computed to be \(-5.552\) and \(-1.771\) eV, respectively. Similarly, the energies of the HOMO and LUMO of 2o are \(-5.410\) and \(-2.079\) eV, respectively.