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 the 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 (C 14/15 ) and varying degrees of chlorination. The molar distribution of C n H 2 n+ 2 –m Cl m in each mixture was determined using high-resolution mass spectrometry (MS). Next, the mixtures were analyzed by applying both one-dimensional 1 H, 13 C and two-dimensional 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 that used massive NMR databases predicted by a neural network algorithm to provide the top 100 most likely structural matches was developed. The top 100 isomers appear to be an adequate representation of the overall mixture. Their modeled physicochemical and toxicity parameters agree with previous experimental results. Chlorines are not evenly distributed in any of the CP mixtures and show a 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.

Predicting Partition Coefficients of Short-Chain Chlorinated Paraffin Congeners by COSMO-RS-Trained Fragment Contribution Models

“…A recent study suggested that the first, second, and third carbons from an end of the chain and central carbons all have differing likelihood of chlorination. 19 Also, it has been known that chlorination occurs less likely to the neighbors of the carbon that is already chlorinated due to a steric effect, 20,21 which is also inferred by GC retention measurements for CP mixtures. 4,22 Nevertheless, in highly chlorinated CP mixtures, dichloro-substituted carbons and trichloromethyl groups have also been identified.…”

“…4,22 Nevertheless, in highly chlorinated CP mixtures, dichloro-substituted carbons and trichloromethyl groups have also been identified. 19,23 Since general rules for positions of Cl for CPs of different lengths and chlorination degree are still under investigation, we opted for the fully random and "one Cl per C" rules to generate congener sets for this work.…”

Predicting Partition Coefficients of Short-Chain Chlorinated Paraffin Congeners by Combining COSMO-RS and Fragment Contribution Model Approaches

“…Third, the current work used randomly generated congeners from all Cl substitution patterns or excluding double and triple Cl substitutions to represent the congener composition of each CP congener group, but this is a first approximation. As more and more knowledge regarding Cl substitution patterns in the bulk CP mixtures is becoming available, 19,23,31 congener compositions used for the prediction of partition coefficients could be elaborated further.…”

“…A recent study suggested that the first, second, and third carbons from an end of the chain and central carbons all have differing likelihood of chlorination. 19 Also, it has been known that chlorination occurs less likely to the neighbors of the carbon that is already chlorinated due to a steric effect, 20,21 which is also inferred by GC retention measurements for CP mixtures. 4,22 Nevertheless, in highly chlorinated CP mixtures, dichloro-substituted carbons and trichloromethyl groups have also been identified.…”

“…4,22 Nevertheless, in highly chlorinated CP mixtures, dichloro-substituted carbons and trichloromethyl groups have also been identified. 19,23 Since general rules for positions of Cl for CPs of different lengths and chlorination degree are still under investigation, we opted for the fully random and "one Cl per C" rules to generate congener sets for this work.…”