Isomerization of Indole. Quantum Chemical Calculations and Kinetic Modeling

Abstract

Density functional theory calculations were carried out to investigate the pathways of the unimolecular isomerizations of indole. Equilibrium and transition-state structures were optimized by the Lee−Yang−Parr correlation functional approximation (B3LYP) using the Dunning correlation-consistent polarized double-ξ basis set. Energy values were calculated at the CCSD(T) level of theory. Rate parameters for all the steps on the surfaces of the indole isomerizations were evaluated using B3LYP frequencies and CCSD(T)//B3LYP energy values. 3H-Indole, which is a stable tautomer of indole, is a precursor in the formation of o-tolyl isocyanide that by −NC → −CN flip forms o-tolunitrile. The latter is one of the isomers of indole. A second isomer, phenylacetonitrile, is obtained directly from indole. A kinetics scheme containing all the elementary steps on the surfaces was constructed, apparent rate constants for product formation were calculated, and comparison with experimentally available formation rates was made. The agreement for phenylacetonitrile is excellent. For o-tolunitrile the calculations somewhat underestimate the rate. Despite many efforts, a reaction path for the formation of m-tolunitrile based on indole as a starting point could not be calculated with activation energies compatible with the experimental findings. On the other hand, a reaction path for the isomerization starting from indole radical, with low-lying transition states and intermediates, was calculated. It is therefore suggested that indole radicals that are formed by various abstraction reactions are involved in the isomerization of indole to m-tolunitrile.

High resolution photofragment translational spectroscopy of the near UV photolysis of indole: Dissociation via the1πσ* state

“…Modelling of relative product yields arising in the pyrolysis of indole suggests that such highly internally excited ground state molecules will isomerise and undergo ring-opening reactions on timescales that are much faster than this rate of unimolecular decay, and that at least three other H atom elimination pathways [all within B3000 cm À1 of the lowest dissociation limit, (D 0 (H-indolyl))] thus require consideration. 39,40 We also observe H atoms (as H 1 ions) at dt >1 ms via TOF-MS (Fig. 2(d)).…”

Chemical Behavior of a Pair of (COD)CpRh and −Ir Complexes with Pendant Peripheral −B(C6F5)2Groups

“…It features the typical spectroscopic data of a [(COD)IrCp-CH 2 CH 2 CH 2 B(C 6 F 5 ) 2 ]/1-methylimidazole adduct (see Table 1 and Scheme 4). We observed 11 B and 19 F NMR shifts characteristic of the B-N-type structure, a 2:2 intensity pair of C 5 H 4 -1 H NMR resonances (δ 5.00/4.72; corresponding 13 C NMR signals at δ 82.3, 80.2; C-ipso at δ 103. 6) and only one pair of COD 13 C NMR resonances (δ 47.3, 34.5, 1 H NMR signals at δ 3.74, 2.21/1.97).…”

“…Consequently, the -C 6 F 5 substituents at boron are different, i.e., positioned cis or trans to iridium. In addition this crowded structural situation has led to an increased rotational barrier around both B-C 6 F 5 vectors, so that the 19 3). As expected the p-F NMR signals do not show coalescence behavior.…”

“…As expected the p-F NMR signals do not show coalescence behavior. From this temperature-dependent dynamic 19 F NMR behavior Gibbs activation energies of ∆G q rot (233 K) ≈ 10.1 ( 0.2 kcal mol -1 were estimated for the hindered rotation around the cis-and trans-B-C 6 F 5 vectors 16 in complex 13.…”

Photoinduced transformations of indole and 3-formylindole monomers isolated in low-temperature matrices

“…The form 3Hindole (also called indolenine) was the subject of several investigations. [27][28][29][30][31] Indolenine was generated by pyrolysis of gaseous indole 29 or, alternatively, by photodecomposition of N-indolinylacetophenone in aqueous solution. 29 At temperatures above 50 • C, indolenine rapidly transforms back into 1H-indole.…”