scholarly journals The Molecular Structure of 2,5-Dihydrofuran from the Analysis of the Nematic Liquid Crystal Nuclear Magnetic Resonance Spectrum

1974 ◽  
Vol 52 (2) ◽  
pp. 281-286 ◽  
Author(s):  
K. C. Cole ◽  
D. F. R. Gilson
Keyword(s):  
Molecular Structure ◽  
Nuclear Magnetic Resonance ◽  
Liquid Crystal ◽  
Magnetic Resonance ◽  
Nuclear Magnetic Resonance Spectrum ◽  
Nematic Liquid Crystal ◽  
Nematic Phase ◽  
Resonance Spectrum ◽  
Coupling Constants ◽  
Ring Puckering

The nematic phase n.m.r. spectrum of partially oriented 2,5-dihydrofuran has been analyzed. Corrections to the structure for ring puckering and methylene rocking motions, according to the model due to Malloy, give improved agreement between experimental and calculated direct dipole–dipole coupling constants.

Nematic phase nuclear magnetic resonance studies of the molecular structures of cyclobutanone and methylenecyclobutane

1976 ◽  
Vol 54 (4) ◽  
pp. 657-664 ◽  
Author(s):  
K. C. Cole ◽  
D. F. R. Gilson
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nematic Phase ◽  
Proton Magnetic Resonance ◽  
Molecular Structures ◽  
Coupling Constants ◽  
Magnetic Resonance Studies ◽  
Dipole Coupling ◽  
Nmr Data ◽  
Ring Puckering

The nematic phase proton magnetic resonance spectra of cyclobutanone and methylenecyclobutane have been analyzed and the direct dipole coupling constants corrected for the averaging effects of the ring puckering vibrations. The nmr data have been used in conjunction with microwave spectroscopic results to derive the molecular structures.

A precise analysis of the 1H nuclear magnetic resonance spectrum of 2-phenyl-1,3-dithiane. Ring pucker, signs of long-range J(H,H), internal rotational barrier, and van der Waals shifts

1994 ◽  
Vol 72 (7) ◽  
pp. 1722-1727 ◽  
Author(s):  
Ted Schaefer ◽  
Jeremy P. Kunkel ◽  
Robert W. Schurko ◽  
Guy M. Bernard
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nuclear Magnetic Resonance Spectrum ◽  
Resonance Spectrum ◽  
Chemical Shifts ◽  
Van Der Waals ◽  
Lone Pair ◽  
Coupling Constants ◽  
Van Der Waals Interactions ◽  
Nuclear Magnetic

The 1H nuclear magnetic resonance spectrum of 2-phenyl-1,3-dithiane, as a dilute solution in a CS2–C6D12–TMS solvent mixture at 300 K, is analyzed to yield 8 chemical shifts and 22 distinct coupling constants, nJ(H,H), n = 2–6. The coupling constant between H-2 and the para proton indicates, first, that the bisected conformer (phenyl plane perpendicular to the pseudo plane of the dithiane ring) is most stable and, second, that the apparent twofold barrier to rotation about the Csp2—Csp3 bond is 9.6 kJ/mol. The AM1, STO-3G, and STO-3G* computations confirm the twofoldedness of the barrier; the AM1 barrier is 9.4 kJ/mol. The empirical equation, [Formula: see text] reproduces the vicinal coupling constants of the CH2CH2CH2 fragments and implies puckering angles [Formula: see text] of 54°, 61°, and 64°, respectively. It is implied that 3J at [Formula: see text] is larger than at [Formula: see text] This results is discussed in terms of the latest theoretical approach to 3J in the HCCH fragment. The 4J(H,H) signs and magnitudes for the CH2CH2CH2 fragment agree reasonably well with theory. For the CH2SCH fragment, 4J(H,H) values are positive, in contrast to corresponding numbers in the propanic fragment, perhaps the first experimental values for certain rigid orientations about a heteroatom. INDO MO FPT computations on propane, dimethyl ether, and dimethyl sulfide confirm the experimental trend in 4J(H,H). 2J(H,H) and 5J(H,H) values are compared to those in related molecules. The striking differential shifts of the axial and equatorial protons are attributed to differential van der Waals interactions with the 3p lone-pair orbital on sulfur. A comparison of the ring proton chemical shifts with those in phenylcyclohexane and isopropylbenzene implies that C—S bonds are weaker net electron donors by hyperconjugation than are C—C bonds. It is also proposed that the ortho protons are deshielded by intramolecular van der Waals interactions with the 3p orbitals on the sulfur atoms.

129Xe and 2H nuclear magnetic resonance (NMR) of xenon and deuterated-chloroform solutes in a thermotropic biaxial nematic liquid crystal

2011 ◽  
Vol 89 (9) ◽  
pp. 1143-1149 ◽  
Author(s):  
P. Tallavaara ◽  
A.M. Kantola ◽  
J. Jokisaari ◽  
T. Meyer ◽  
D.A. Wilson ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Liquid Crystal ◽  
Magnetic Resonance ◽  
Nematic Liquid Crystal ◽  
Nematic Phase ◽  
Deuterated Chloroform ◽  
H Nmr ◽  
Clear Change ◽  
Biaxial Nematic ◽  
Nuclear Magnetic

Properties of a thermotropic nematic liquid crystal (LC) TM35 (organosiloxane tetrapode) were investigated by means of nuclear magnetic resonance (NMR) spectroscopy of probe atoms and molecules. 129Xe isotope enriched xenon gas and 2H isotope enriched chloroform were used as probes. Both 129Xe and 2H NMR measurements were carried out over a wide temperature range, covering isotropic, nematic, and glass phases. A clear change in the behavior of the LC is observed within the nematic phase at 289 K by changing the temperature from low to high and inspecting the spectral line width. The derivative curve of the 129Xe chemical shift also reveals a change at 289 K. These changes may be an indication of hindered molecular rotation around the long axis, and the appearance of a biaxial nematic phase.

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