High-Field Chlorine NMR Spectroscopy of Solid Organic Hydrochloride Salts: A Sensitive Probe of Hydrogen Bonding Environment

Abstract

A series of organic hydrochloride salts has been investigated using solid-state 35Cl and 37Cl NMR spectroscopy at applied magnetic field strengths of 9.4 and 18.8 T. Magic-angle spinning, static Hahn-echo, and quadrupolar Carr−Purcell Meiboom−Gill (QCPMG) echo experiments have been applied to investigate the chlorine electric field gradient (EFG) and chemical shift (CS) tensors for l-tyrosine hydrochloride, l-cysteine methyl ester hydrochloride, l-cysteine ethyl ester hydrochloride, quinuclidine hydrochloride, and tris sarcosine calcium chloride. Chlorine-35 nuclear quadrupolar coupling constants for these compounds range from 2.23 to 5.25 MHz, and isotropic chemical shifts range from approximately 9 to 53 ppm relative to the chloride ion in aqueous solution. The results demonstrate the feasibility and benefits of high-field 35/37Cl NMR studies of organic chloride salts. A discussion of the data in the context of the known X-ray or neutron diffraction structures for these compounds suggests that the chlor...