Chlorines Are Not Evenly Substituted in Chlorinated Paraffins: A Predicted NMR Pattern Matching Framework for Isomeric Discrimination in Complex Contaminant Mixtures

Abstract

Chlorinated paraffins (CPs) can be mixtures of nearly a half million possible isomers. Despite extensive use of CPs, their isomer composition and effects on the environment remain poorly understood. Here, we reveal the isomeric distributions of nine CP mixtures with single chain lengths (C14/15) and varying chlorination degrees. The molar distributions of CnH2n+2-mClm in each mixture was determined using high-resolution mass spectrometry (MS). Next, the mixtures were analyzed by applying both one-dimensional (1D) 1H, 13C and two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy. Due to substantially overlapping signals in the experimental NMR spectra, direct assignment of individual isomers was not possible. As such, a new NMR spectral matching approach was developed that used massive NMR databases predicted by a neural network algorithm to provide the top 100 most likely structural matches. The top 100 isomers appear to be an adequate representation of the overall mixture. Their modelled physicochemical and toxicity parameters agree with previous experimental results. Chlorines are not evenly distributed in any of the CP mixtures and show general preference at the third carbon. The approach described here can play a key role in understanding of complex isomeric mixtures such as CPs that cannot be resolved by MS alone.