The Electric Field Gradients at the Nitrogen and Chlorine Sites in 1,2,4,5‐Tetrachloro‐3,6‐Dinitrobenzene and 1,3,5‐Trichloro‐2,4‐Dinitrobenzene. A ¹⁴N NMR and ³⁵Cl NQR Single Crystal Study

Abstract

Chemical Bond / Molecular Structure / Spectroscopy, Nuclear Magnetic Resonance Resonance "CI and I4N nuclear quadrupole coupling tensors were determined at 295 K for 1,2,4,5-tetrachloro-3,6-dinitrobenzene and 1,3,5-trichloro-2,4-d1nitrobenzene. The Zeeman split single crystal "Cl NQR gives the quadrupole coupling constant e2qQh 1(3JC1) = 76.937(4) MHz and the asymmetry parameter q(3'CI) = 0.1207(5) for 1,2,4,5-tetrachloro-3,6-dinitrobenzene, and e2qQh-'(35C1"1) = 74.672(6) MHz, (20), e2qQh-1('5C1(5)) = 74.422(6) MHz, q(3'C1(51) = 0.1143(10) for 1,3,5-trichloro-2,4-dinitrobenzene. By high field NMR e2qQh-' (14N) and q(14N) were determined at 295 K . For 1,2,4,5-tetrachloro-3,6dinitrobenzene it is found e2qQh-'(14N) = 0.757(2) MHz, q(14N) = 0.025(3). QrZI('*N) deviates from the bond direction C-N by about 3.3", QXx is parallel to the benzene ring plane . For 1,3,5-trichloro-2,4-dinitrobenzene it is found: e2qQh-'('4N'2)) = 0.722(2) MHz, 4('4N(21) = 0.069(3), e2qQh-'('4N'41) = 0.738(2) MHz, q('4N(4') = 0.064(3). @zI (14N(21) and @zz(14N(4)) nearly coincide with the corresponding C -N bond directions. @xx('4N'4') is nearly parallel to the benzene ring plane, whereas @xx (14N(2)) is twisted about 18" against the ring plane.The relation between the twist angle Y and the asymmetry parameter of the ''N electric field gradient is discussed.

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

“…A comparable value, 5.027 MHz, has been determined for cocaine hydrochloride. 25 Certainly NQR spectroscopy has been used to determine much larger quadrupolar coupling constants, 26 e.g., C Q ( 35 Cl) in 1,2,4,5-tetrachloro-3,6-dinitrobenzene is 76.937 MHz 67 and C Q ( 35 Cl) in solid Cl 2 at 0 K is 108.975 MHz. 68 A value of -145.87 MHz has been determined by molecular beam electric resonance spectroscopy for the ground vibrational state of gaseous ClF.…”

35Cl and 37Cl Magic-Angle Spinning NMR Spectroscopy in the Characterization of Inorganic Perchlorates

“…Furthermore, for large 35 Cl quadrupole couplings a substantial second-order quadrupolar broadening of the central transition may hamper the observation of 35 Cl resonances in powdered solids. For example, the very large 35 Cl quadrupolar couplings for covalently bonded chlorine in organic compounds (i.e., 20 ≲ C Q ≲ 80 MHz) , imply that the 35 Cl quadrupolar couplings can only be determined from single-crystal NMR, nuclear quadrupole resonance (NQR), ,, or static-powder NMR with the carrier frequency being incremented over the entire spectral width for the central transition . For chloride ions in highly symmetric environments, the quadrupole couplings become smaller and thereby allow standard static-powder and magic-angle spinning (MAS) NMR methods to be employed.…”

“…The two naturally occurring chlorine isotopes, 35 Cl and 37 Cl, both have nuclear spin I ) 3 / 2 and almost identical gyromagnetic ratios and quadrupole moments. Although both isotopes are amenable to NMR experiments, the threefold-higher natural abundance for 35 Cl (75.53%) makes this the more attractive NMR isotope of the two.…”

An NQR study of the crystalline structure of TNT

“…A strong correlation of twist angle with asymmetry parameter has also been found in many other aromatic compounds 8 . The twist angles for TNT were obtained from the work of Duke 9 and later values are quoted in reference 4; theoretical calculations have also been made and compared with the X-ray values 10 .…”