35 Cl NQR, Crystal Structure, and C-Cl Bond Length of Cyclohexadienones

1989

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.

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

Wigand

Weiden

1989

Crystal Structure and Nuclear Quadrupole Resonance. The Bond Length C — Cl and ³⁵Cl NQR

Brummer

1990

Self Cite

The intramolecular distances dC—Cl for chlorine bound to sp2 carbon and to sp3 carbon, respectively, and the 35Cl NQR frequencies assigned to the corresponding Cl atoms correlate quite well according to the theory: v(35Cl) ∼ (dC—Cl)−3. The relation is v(35Cl) = (4 ± 6) MHz + (166 ± 31) · 106 · (dC—Cl)−3 · MHz · pm3 for {sp2‐C}‐Cl and v(35Cl) = (21 ± 5) MHz + (101 ± 25) · 106 · (dC—Cl)−3 · MHz · pm3 for {sp3‐C}‐Cl. — The crystal structures and chemical bonds of 1 (4‐methyl‐4‐trichloromethyl‐2,5‐cyclohexadiene‐1‐one), 2 (2‐chloro‐4,5‐dimethyl‐4‐trichloromethyl‐2,5‐cyclohexadiene‐1‐one), 3 (4,5‐dichloro‐1‐phenyl‐pyridazine‐6‐one), and 4 (2,2,4,5‐tetrachloro‐cyclo‐pentene‐1,3‐dione) were studied by single crystal X‐ray diffraction and 35Cl nuclear quadrupole resonance (NQR). 1 crystallizes with the space group D152h‐Pbca, Z = 8. The lattice constants are a = 1206.0(3) pm, b = 1341.3(3) pm, and c = 1178.8(3) pm. 2 crystallizes monoclinic, space group C52h‐P21/c, Z = 4, a = 696.3(3) pm, b = 1404.0(5) pm, c = 1151.4(5) pm, and β = 100.23(1)°. 3 crystallizes in the orthorhombic space group D4h‐P212121, Z = 4, a = 4303(1) pm, b = 586.8(2) pm, and c = 390.5(1) pm. 4 crystallizes cubic, space group T4h‐Fd3, with 48 molecules in the unit cell, a = 2181.5(5) pm. The 35Cl NQR spectra were observed for the two 2,5‐cyclohexadiene‐1‐ones, 1 and 2 in the temperature range 77 < T/K < melting point. For 3, the 35Cl NQR spectra was determined at T = 77 K and T = 295 K. No phase transition has been found for the three compounds in the temperature range in which the 35Cl NQR spectroscopy was performed.

On the Persistence of Molecular Symmetry in the Solid State and the Role of Molecular Group Dipole Moments. Centrosymmetry in Bis‐(Chloromethyl)benzenes

Basaran

Dou

1992

The crystal structures and the 35Cl NQR spectra of 1,4‐bis(chloromethyl)‐2,3,5,6‐tetrachlorobenzene, 1,4‐(CH2Cl)2C6Cl4; 1,4‐bis(chloromethyl)‐2,3,5,6‐tetramethyl‐benzene, 1,4‐(CH2Cl)2C6(CH3)4; 1,4‐bis(chloromethyl)benzene, 1,4‐(CH2Cl)2C6H4; 1,2‐bis(chloromethyl)benzene, 1,2‐(CH2Cl)2C6H4 are reported. – The compounds 1,4‐(CH2Cl)2C6Cl4 and 1,4‐(CH2Cl)2(CH3)4 are isostructural, space group C–P1, Z = 1. 1,4‐(CH2Cl)2C6Cl4: a = 893.1(4) pm, b = 655.1(3) pm, c = 494.5(2) pm, α = 98.32(2)°, β = 96.87(2)°, γ = 103.60(2) 92°; 1,4‐(CH2Cl)2C6(CH3)4: α = 902.3(4) pm, b = 809.4(4) pm, c = 442.5(2) pm, α = 87.38(2)°, β = 83.02(2)°, γ = 65.00(2)°. 1,4‐(CH2)2C6H4 crystallizes monoclinic, C–P21/c, Z = 2, a = 848.8(4) pm, b = 465.0(2) pm, c = 1042.2(5) pm, β = 99.21(2)°. 1,2‐(CH2Cl)2C6H4 is noncentrosymmetric, orthorhombic, C–Fdd2, Z = 8, a = 1562.0(4) pm, b = 1358.0(3) pm, c = 790.4(2) pm. – The 35Cl NQR spectra of 1,4‐(CH2Cl)2C6(CH3)4, 1,4‐(CH2Cl)2C6H4, and 1,2‐(CH2Cl)2C6H4 are singlets, with negative temperature coefficients dν(35Cl)/dT over the temperature range 77 K–Tmelt and the frequencies are in the range 34.4 ≥ ν(35Cl)/MHz ≥ 31.8. 1,4‐(CH2Cl)2C6Cl4 shows a 35Cl NQR triplet, with negative temperature coefficients for 77 ≤ T/K ≤ 420, 37.5 ≥ ν(35Cl)/MHz ≥ 33.8, too. In this compound a phase transition occurs, with a wide hysteresis, Tc, up = 366 K, Tc, down = 328 K. The inductive effect on the 35Cl NQR in the CH2Cl group is strong. – In molecular crystals the complete symmetry of the free molecule seldom persists in the solid state. The molecular symmetry in the condensation process is fully or partially lost due to the van der Waals interaction of neighboring molecules. The compensation of the partial dipole moments of the two chloromethyl group in para position retains the molecular symmetry Ī in the solid phases. It will be discussed that in benzene derivatives either Ī, m or 2 are the “hard” symmetry elements, preserved in the solid state.