# A McLafferty-Type Rearrangement in the Pentafluorobenzyl Ester Derivatives of Dialkyl Phosphates in GC-NICI-MS/MS: A Mini-Review and a Meta-Analysis

## TL;DR

This paper reports a rare McLafferty-type rearrangement in negative-ion mass spectrometry of pentafluorobenzyl esters of dialkyl phosphates.

## Contribution

First observation of a McLafferty rearrangement in NICI-MS/MS of pentafluorobenzyl esters of organophosphates.

## Key findings

- McLafferty rearrangements were observed in CID of [M−PFB]− ions from pentafluorobenzyl esters of diethyl phosphates.
- Two specific product anions formed via α,β-cleavage and neutral losses of ethene and ethanol.
- No rearrangements were observed in NICI of diethyl fluoro phosphate or in PICI mode.

## Abstract

Rearrangements such as the McLafferty rearrangement are common in mass spectrometry of positive ions, but rare in negative ions. The present article searched the literature for McLafferty rearrangements of negative ions formed by negative electrospray ionization (-ESI) or by negative-ion chemical ionization (NICI). McLafferty Rearrangements have been reported for negative ions formed by -ESI, yet not for anions formed by NICI in GC-MS and GC-MS/MS. This article reports for the first time a McLafferty Rearrangement of the collision-induced dissociation (CID) of precursor ions due to [M−PFB]− generated by NICI in the GC-MS/MS analysis of pentafluorobenzyl (PFB) esters and thioesters of diethyl phosphates (CH3CH2O)2PO2, diethyl thiophosphates (CH3CH2O)2PSO, and diethyl dithiophosphates (CH3CH2O)2PS2. Two specific product anions due to α,β-cleavages and formation of neutral losses of ethene and ethanol are formed. No McLafferty rearrangements were observed in the CID of 1-chloropropyl derivatives of these dialkyl organophosphates in the positive-ion chemical ionization (PICI) mode. McLafferty rearrangements of PFB esters of organophosphates have been observed in the EI mode. No McLafferty rearrangements were observed in the EI and NICI of diethyl fluoro phosphate, a representative of dialkyl fluoro phosphates. McLafferty rearrangements of negative ions seem to be more common than assumed so far.