Effect Of Benzo-annelation Research Articles

Effect of Benzo-Annelation on Triplet State Energies in Polycyclic Conjugated Hydrocarbons.

In a series of earlier studies, the effect of benzo-annelation was found to be a useful tool for tuning the aromaticity in polycyclic conjugated compounds to desired level. In this work we studied the (anti)aromaticity of benzo-annelated derivatives of three conjugated hydrocarbons (anthracene, fluoranthene and biphenylene) in their lowest lying singlet (S0) and triplet (T1) states by means of the energy effect (ef), harmonic oscillator model of aromaticity (HOMA), multicentre delocalization indices (MCI), magnetically induced current densities (MICDs) and nucleus independent chemical shifts (NICS). We showed that benzo-annelation is a topology-based effect which can be used to modify the T1 state excitation energies (E(T1)). A quantitative model was established being able to accurately predict the E(T1) based only on the numbers of angularly, linearly and geminally annelated benzene rings. In addition, it was demonstrated that the E(T1) can be directly related to the (anti)aromatic character of the central ring in the studied molecules in their S0 state.

Effect of benzo-annelation on magnetically induced current density

The effect of benzo-annelations on the magnetically induced current density was analyzed by means of the integrated current strengths. The magnetically induced current densities were computed using the diamagnetic-zero version of the continuous transformation of origin of current density (CTOCD-DZ) method at the B3LYP/6-311G(d,p) level of theory. It was found that benzo-annelation in the angular (respectively linear) position relative to the central rings of the studied anthracene and acridine derivatives decreases (respectively increases) the intensity of the π-electron currents that flow around the central ring. These regularities were further analyzed by recently introduced the pairwise fragment interaction (PFI) method.

Effect of benzo-annelation on local aromaticity in heterocyclic conjugated compounds.

The effect of benzo-annelation on the local aromaticity of the central ring of acridine (1), 9H-carbazole (2), dibenzofuran (3), and dibenzothiophene (4) was analyzed by means of the energy effects (ef), pairwise energy effects (pef), multicenter delocalization index (MCI), electron density at ring critical points (ρ(r(C))), harmonic oscillator model of aromaticity (HOMA), and nucleus independent chemical shifts (NICS). According to energetic, electron delocalization, and geometrical indices, angular benzo-annelation increases, whereas linear benzo-annelation decreases, the extent of the local aromaticity of the central ring containing heteroatoms. The local aromaticity of the central heterocyclic ring in the examined molecules can significantly vary by applying different modes of benzo-annelation. The NICS values do not always support the results obtained by the other aromaticity indices and, in some cases, lead to completely opposite conclusions.

Local Aromaticity in Benzo- and Benzocyclobutadieno-Annelated Phenanthrenes

The effects of benzo- and benzocyclobutadieno-(BCBD-)annelation on the local aromaticity of the central ring (X) of phenanthrene were examined. The local aromaticity of the ring X was estimated using a graph-theory-based index and two geometry-based indices. DFT calculations of phenanthrene congeners showed that many of these molecules are nonplanar, with significant steric strain. All three indices indicate that the effect of benzo-annelation is opposite to that of BCBD-annelation. The deviation of some phenanthrene derivatives from planarity does not influence the effects of annelation. This finding is in accord with some previously reported studies on the dependence of the aromaticity of the ring(s) on distortion from planarity.

Effect of benzo-annelation on cyclic conjugation

Earlier studies revealed that the effect of benzo-annelation on cyclic conjugation in the central ring of a polycyclic conjugated molecule obeys certain general regularities. We now elaborate quantitative models of this effect, showing that the main factors that need to be taken into account are the numbers of angularly, linearly, and geminally annelated rings.

Effect of benzo annelation on the Chichibabin reaction

The kinetics of amination with sodium amide (the Chichibabin reaction) for six azines and five azoles and the kinetics of the piperidinolysis of 2-chloro-substituted azole systems were studied. The following orders of reactivities were established for the Chichibabin reaction: isoquinoline > phenanthridine > benzo[h]quinoline > benzo[f]quinoline > pyridine ≫ acridine and 1-methylbenzimidazole > 1-methylnaphth[2,3-d]imidazole > 1-methylperimidine > 1-methylnaphth[1,2-d]imidazole > 3-methylnaphth-[1,2-d]imidazole. The changes in the reactivities are explained by the changes in the hydride labilities of the corresponding σ complexes.