3-Methylindole, comparison

Figure 2 Solvent effect on the quenching rate constant of 3-methylindole. Comparison between experimentally determined k.Q values in homogeneous solvents and those calculated using Eq. (17) (adapted from Ref. 14). The experimentally determined value of kap in SDS micelles ( ) and the value of k(j estimated from Eq. (21) (A) have been included.

In the case of P(III) acid dichlorides, in which the electrophilicity of the phosphorus atom is increased in comparison with that of monochlorides, a decrease in the selectivity of N-phosphorylation must be expected. In fact, the reactions of indole and 2-methylindole with dichloroamidophosphites, dichlorophosphites, and dichlorophosphines lead to bisindolylphosphonites, bisindolylphosphines, and bisindolylphosphinites 18-20 [11,12]. 

A direct comparison between 1-methylindole and 1-methylpyrrole is possible only for an a-carbonium ion reaction, the solvolysis of... 

Figure 6. Comparison of SRC-II mass 132 MS/MS ("upper,) with the reference spectrum of 3-methylindole ("lower)...

A theoretical determination of vibrational absorption and Raman spectra of 3-methylindole radicals has been carried out in comparison to experimentally measured spectra for 3-methylindole (Table 28) to provide specific spectroscopic markers for the detection of neutral or cationic tryptophan radicals in biological systems <2001CPH(265)13>. Among isatin derivatives, substitution at C-5 has relatively greater influence on the electron density and the force constant of the amide than of the ketone carbonyl group (Table 29) <2001SAA469>. 

Comparison with the spectra of A7-substituted indoles also provides a means of detecting the N-H signals. Figure 4A and B illustrate23 the application of this device in the case of indole and iV-methylindole, wherein the triplets due to a- and /3-protons of indole are reduced to doublets in iV-methylindole, forming the simpler AB pattern. The N-H peak disappears in Fig. 4B and, hence, provides the location of the 1-proton signal in indole. 

HMO calculations on cycl[3.2.2]azine (240)26-26 attributed substantial DE to the molecule and more recently Dewar and Trinajstic462 calculated a value for the Dewar resonance energy of 18.9 kcal mole-1. The aromaticity of 240 is reflected in the PMR spectrum101 which shows proton resonances in the region 7.20 to 7.86 ppm. Paudler and Shin463 examined an isomer of 240, viz., pyrrolo[3,2,1-/, i]indole (241), and from a comparison of the benzene-induced shifts of the proton resonances in both 241 and 7-methylindole suggested that there is no loss of aromaticity in 241 relative to the indole derivative. A further comparison of the proton chemical shifts in 241 and its dihydro derivative 242 led the authors to suggest that the former is the more aromatic. 

L. Dubois, A. Mehta, E. Tourette, and R. H. Dodd, Preparation of p-substituted tryptophan derivatives—comparison of the reactivity of JV-methylindole toward aziridine-2-lactones and aziridine-2-carboxylic esters and interpretation of results using MNDO calculations, J. Org. Chem., 59 (1994) 434- 1. 

We might ask just how reactive indole is in comparison with other aromatic rings. Mayr and his coworkers have carried out extensive studies on relative nucleophi-licity, N, by examining reactivity towards a series of benzhydryl carbocations [1]. In this comparison, indole was found to have the relative reactivity 5.55. The 1 -methyl (5.75) and 1,2-dimethyl derivatives are more reactive, while 2-methylindole is somewhat less reactive (4.42) because of its steric effects [2]. Pyrrole is less reactive with an N value of 4.63. Indole is substantially less reactive than representative enamines, such as 1-pyrrrolidinocyclohexene, for which N is 14.91 [3]. Being a logarithmic scale, this indicates that indole is some 15 times more reactive than pyrrole, but 10 ° less reactive than the cited enamine. For simpler aromatics, 1,3-dimethoxybenzene is assigned an N value of 2.48 and toluene, —4.47 Thus, indole is about 10 ° more reactive than toluene. 

At the same time, there is a very interesting observation about indole and methylindole revealed by Py-GC/MS as products of thermal decomposition of tryptophan in egg white, because this amino acid is absent in animal glue and is usually lost in the acid hydrolysis workup common to conventional GC and HPLC. Also, there is a very detailed comparison between conventional techniques (Uke GC aud HPLC) and analytical pyrolysis methods in the end of the article. 

FIGURE 6.30 Comparison between the kinetic model calculation and the experimental yields of 2-methylindene ring expansion (a) [115] and between the calculated and the experimental rate constants of methylindole interisomerizations (b) [119]. 

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