Comprehensive quantum chemical and mass spectrometric analysis of the McLafferty rearrangement of methyl valerate.

The McLafferty rearrangement (McLR) of the methyl valerate molecular ion has been comprehensively studied from the standpoints of the timescale for the keto-enol transformation and the change of the configuration of intermediates and transition state (TS), using mass spectrometry with electron ionization, strong-field tunnel ionization and collision-induced dissociation methods, and the global reaction route mapping (GRRM) program with quantum chemical calculations (QCCs). The timescales estimated from mass spectrometric results suggested that the McLR starts at 100 fs after ionization and is completed at least within 100 ns in the ion source. Whereas the timescales are consistent with a stepwise mechanism of fast (100 fs) and slow (10 ps) steps presented by Stamm , the QCCs put forth the possibility that an unanticipated, rapid, concerted process may be involved in completing the McLR reaction.

Quantum Chemical Analysis of Molecular and Fragment Ions Produced by Field Ionization of Methyl Stearate.

The formation of molecular and fragment ions observed in the field ionization mass spectrum of methyl stearate has been analyzed on the basis of quantum chemical calculations including time-dependent density functional theory (TDDFT) and natural bond orbital (NBO) analysis. The TDDFT calculations suggest that methyl stearate is ionized via two processes, namely a 7.43 eV excitation and a tunneling effect, while the high electric field of 10 V/m enables analyte molecules to ionize at an effective 6 eV lower than the 9.

Construction of a Mass Spectrum Library Containing Predicted Electron Ionization Mass Spectra Prepared Using a Machine Learning Model and the Development of an Efficient Search Method.

Electron ionization (EI) mass spectrum library searching is usually performed to identify a compound in gas chromatography/mass spectrometry. However, compounds whose EI mass spectra are registered in the library are still limited compared to the popular compound databases. This means that there are compounds that cannot be identified by conventional library searching but also may result in false positives.

Integrated qualitative analysis of polymer sample by pyrolysis-gas chromatography combined with high-resolution mass spectrometry: Using accurate mass measurement results from both electron ionization and soft ionization.

Rationale: Gas chromatography/mass spectrometry (GC/MS) is a powerful analytical tool used to separate and then identify volatile compounds through library database searches. However, as not all compounds are registered in these databases, it is not uncommon to detect unregistered components. Therefore, new analytical techniques were developed that utilize methods of identification beyond database searches alone.