Unusual Long-Range Spin–Spin Coupling in Norbornane-2,3-diones. Proton Magnetic Resonance Spectrum and X-Ray Structure Analysis of 6-endo-Bromo-1,5,5-trimethylnorbornane-2,3-dione

1973 ◽  
Vol 51 (24) ◽  
pp. 4076-4079 ◽  
Author(s):  
G. F. Hambly ◽  
Jeanette Leitch ◽  
Peter Yates ◽  
S. C. Nyburg
Keyword(s):  
Magnetic Resonance ◽  
Long Range ◽  
Structure Analysis ◽  
Mirror Symmetry ◽  
Proton Magnetic Resonance ◽  
Substituent Effects ◽  
Proton Magnetic Resonance Spectrum ◽  
Spin Coupling ◽  
X Ray ◽  
Spin Spin Coupling

Several norbornane-2,3-diones show in their proton magnetic resonance spectra an unusual long-range spin–spin coupling, 4J46λ = 1.0–1.5 Hz. An X-ray structure analysis of 6-endo-bromo-1,5,5-trimethylnorbornane-2,3-dione shows that the norbornane framework deviates only slightly from mirror symmetry. This makes it unlikely that the unusual coupling in the norbornane-2,3-diones is due to distortion of the norbornane framework and lends credence to the view that it is due to substituent effects.

Proton magnetic resonance spectra of some benzo[b]thiophens. An investigation of substituent effects in a heteroaromatic system

1968 ◽  
Vol 21 (7) ◽  
pp. 1853 ◽  
Author(s):  
B Caddy ◽  
M Martin-Smith ◽  
RK Norris ◽  
ST Reid ◽  
S Sternhell
Keyword(s):  
Magnetic Resonance ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Spin Coupling ◽  
Heteroaromatic System ◽  
Spin Spin Coupling ◽  
Magnetic Resonance Spectra

N.m.r. data for 19 5-substituted and 13 polysubstituted benzo[b]thiophens are tabulated. The influence of the substituents at C5 on the chemical shifts of H4 and H6 is discussed. Long-range interproton spin-spin coupling between H3 and H7, and between H2 and H6, is general in benzo[b]thiophens. The vicinal coupling J6,7 in 5-substituted benzo[b]thiophens varies directly and linearly with the electronegativity of the substituents at C5.

Conformational dependence of long-range spin-spin coupling constants in 2,6-dichlorobenzylfluoride

1969 ◽  
Vol 47 (19) ◽  
pp. 3688-3690 ◽  
Author(s):  
T. Schaefer ◽  
C. M. Wong ◽  
K. C. Tam
Keyword(s):  
Magnetic Resonance ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Double Resonance ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Double resonance experiments on the proton magnetic resonance spectrum of 2,6-dichlorobenzylfluoride yield the signs of the long-range coupling constants between the ring protons and the fluorine nuclei and protons in the fluoromethyl group. The signs and magnitudes of the long-range couplings are discussed in terms of their dependence on the conformation of the fluoromethyl group.

Proton Magnetic Resonance Studies of Rotational Isomerism in Halotoluenes. X. Estimates of Conformational Preferences and Rotational Barriers in Benzal Fluoride and Some Dichloro Derivatives

1974 ◽  
Vol 52 (3) ◽  
pp. 481-488 ◽  
Author(s):  
J. Brian Rowbotham ◽  
Alexander Frank Janzen ◽  
James Peeling ◽  
Ted Schaefer
Keyword(s):  
Magnetic Resonance ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Substituent Effects ◽  
Molecular Orbital Calculation ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Proton Proton ◽  
Carbon Carbon Bond ◽  
Dichloro Derivative

The synthesis of benzal fluoride and of its 2,6-, 3,5-, 3,4-, and 2,4-dichloro derivatives is followed by an analysis of their proton magnetic resonance spectra. The long-range spin–spin coupling constants are most consistent with a barrier to rotation about the sp2–sp3 carbon–carbon bond in benzal fluoride of less than 500 cal/mol, in semiquantitative agreement with an ab initio molecular orbital calculation. The 2,6-dichloro derivative has a conformation in which the C—H bond of the side chain lies in the plane of the aromatic ring. The 2,4-dichloro derivative favors a similar conformation, the C—H bond lying cis to the ring chlorine atom. In contrast to the long-range proton–proton couplings, the long-range proton–fluorine couplings are intrinsically sensitive to substituent effects from the ring chlorine atoms.

scholarly journals Long-range spin–spin coupling in N-methyl 2-carbomethoxy-4,6-dinitroaniline

1970 ◽  
Vol 48 (6) ◽  
pp. 934-941 ◽  
Author(s):  
J. A. McCubbin ◽  
R. Y. Moir ◽  
G. A. Neville
Keyword(s):  
Magnetic Resonance ◽  
Carbonyl Group ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Chemical Shifts ◽  
Relative Magnitude ◽  
Spin Coupling ◽  
Spin Spin Coupling ◽  
Derivatives Of ◽  
Shielding Effects

Long-range coupling [Formula: see text] between the amino proton and the C-5 ring proton of N-methyl 2-carbomethoxy-4,6-dinitroaniline (1) was established unequivocally by comparison of the proton magnetic resonance spectra of the 3-d and 5-d analogs of 1 together with the N-deutero derivatives of the above compounds. Deuterium decoupling experiments indicated that meta-deuterium coupling was of the order of band resolution (< 0.2 Hz). Elucidation of the source of long-range coupling with the amino proton enabled the chemical shifts of the aromatic protons to be assigned. The relative magnitude of these chemical shifts is discussed in terms of the shielding effects operative in the predominant conformer in which the amino hydrogen is intramolecularly hydrogen bonded to the oxygen of the ester carbonyl group.

Molecular Conformation of 4-Thiouridine in Aqueous Solution

1971 ◽  
Vol 49 (14) ◽  
pp. 2449-2452 ◽  
Author(s):  
F. E. Hruska ◽  
K. K. Ogilvie ◽  
A. A. Smith ◽  
H. Wayborn
Keyword(s):  
Aqueous Solution ◽  
Long Range ◽  
Crystalline State ◽  
Molecular Conformation ◽  
Spin Coupling ◽  
Pyrimidine Nucleoside ◽  
Coupling Interaction ◽  
X Ray ◽  
Anti Conformation ◽  
Spin Spin Coupling

β-4-Thiouridine is a component of several tRNA molecules. A recent X-ray study has shown that this pyrimidine nucleoside favors the syn conformation in the crystalline state. The 100 and 220 MHz p.m.r. data and a comparison with those of uridine are presented here. A long-range five-bond spin–spin coupling interaction between the H-5 and -1′ hydrogens is noted. The results are consistent with an anti conformation for 4-thiouridine in an aqueous solution.

A proton magnetic resonance determination of the small rotational barriers about the C—Si bond in phenyl derivatives of chloro and methyl silanes

1977 ◽  
Vol 55 (3) ◽  
pp. 557-561 ◽  
Author(s):  
William J. E. Parr ◽  
Ted Schaefer
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Derivatives Of ◽  
Low Energy Conformations

The long-range spin–spin coupling constants between protons bonded to silicon and ring protons in C6H5SiH3, C6H5SiH2Cl, C6H5SiH2CH3, C6H5SiHCl2, and C6H5SiH(CH3)2 are determined from the proton magnetic resonance spectra of benzene solutions. A hindered rotor treatment of the barrier to internal rotation about the C—Si bond, in conjunction with the coupling constants over six bonds, allows the deduction of the low-energy conformations for C6H5SiH(CH3)2 and for C6H5SiHCl2, as well as of barriers of 1.0 ± 0.2 kcal/mol. The approach becomes less reliable for C6H5SiH2CH3 and for C6H5SiH2Cl and, particularly for the latter compound, the derived barrier is very likely an upper limit only. Ab initio molecular orbital calculations of the conformational energies are reported for C6H5SiH3, C6H5SiH2Cl, and for C6H5SiHCl2.

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