Publisher Summary This chapter provides a large collection of solution data and a thoroughly updated discussion of thermodynamic, kinetic, and structural results. This chapter covers aromatic azoles exclusively—that is, aromatic five-membered rings containing only carbon and nitrogen atoms, and their benzo derivatives. This chapter also discusses parent structure on theoretical grounds. One of the oldest methods to get insight into molecular structure, the study of acid-base properties, is today in rapid development. This is particularly true for the azoles. Gas phase studies of the acidity and basicity of azoles provides information on lone pair interactions, transmission of substituent effects in five-membered rings, relationships between acidity and basicity, aromatic substituent effects of nitrogen-linked derivatives and thermodynamic and kinetic parameters for proton transfer between nitrogen atoms in polyazoles. Because of the biological significance of some azoles (pyrrole, indole, imidazole, benzimidazole) and the consequences of acid–base equilibria in their functions, a continuous interest in the behavior in water is to be expected. In the case of N-unsubstituted imidazoles and pyrazoles, complexation of the pyridine-like nitrogen causes a considerable increase in the acidity of the pyrrolelike nitrogen.

Basicity and Acidity of Azoles

Photoionization mass spectrometry is used to study ionization processes and fragmentation pathways of four prebiotic species, pyrimidine, purine, imidazole and benzimidazole, in the 7–18 eV photon energy region, with synchrotron radiation as excitation source. These molecules are possible precursors of the nucleic acid bases that occur in DNA and RNA. Ionization energies and ion appearance energies are reported. They are compared with electron impact and other studies and are discussed in terms of the electronic and nuclear structures of these species and their cations. The ion appearance energies, in conjunction with thermochemical data, were used to propose dissociative photoionization pathways, principally involving loss of HCN molecules in each of the four species. Astrophysical implications of the results concern the prospects for observation and survival of these molecules in the interstellar medium, in comets and in meteorites. Suggestions are made concerning suitable sites for radioastronomical searches for these purines and pyrimidines.

VUV photophysics and dissociative photoionization of pyrimidine, purine, imidazole and benzimidazole in the 7–18 eV photon energy range

Basicity of azoles. IV. Empirical relationships between basicity and ionization potential for aromatic five membered rings containing nitrogen or oxygen

Gas-phase formation of temporary negative ion states via resonance attachment of low-energy (0–6 eV) electrons into vacant molecular orbitals of indoline (I), indene (II), indole (III), 2-methylen-1,3,3-trimethylindoline (IV), and 2,3,3-trimethyl-indolenine (V) was investigated for the first time by electron transmission spectroscopy (ETS). The description of their empty-level structures was supported by density functional theory and Hartree-Fock calculations, using empirically calibrated linear equations to scale the calculated virtual orbital energies. Dissociative electron attachment spectroscopy (DEAS) was used to measure the fragment anion yields generated through dissociative decay channels of the parent molecular anions of compounds I-V, detected with a mass filter as a function of the incident electron energy in the 0–14 eV energy range. The vertical and adiabatic electron affinities were evaluated at the B3LYP/6-31+G(d) level as the anion/neutral total energy difference. The same theoretical method is also used for evaluation of the thermodynamic energy thresholds for production of the negative fragments observed in the DEA spectra. The loss of a hydrogen atom from the parent molecular anion ([M-H]−) provides the most intense signal in compounds I-IV. The gas-phase DEAS data can provide support for biochemical reaction mechanisms in vivo involving initial hydrogen abstraction from the nitrogen atom of the indole moiety, present in a variety of biologically important molecules.

Electron attachment to indole and related molecules

Photoelectron spectroscopy of heterocycles. Azaindenes and azaindolizines

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

L. Klasinc

Author Tools

Chat about Author

Papers

Photoelectron spectroscopy of heterocycles. Azaindenes and azaindolizines