Configuration and Conformation of N,N'-Diarylamidines: A Dipole Moment Study

1993 ◽  
Vol 58 (1) ◽  
pp. 105-112 ◽  
Author(s):  
Václav Všetečka ◽  
Janusz Oszczapowicz ◽  
Otto Exner
Keyword(s):  
Dipole Moment ◽  
Conformational Equilibrium ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Prototropic Rearrangement ◽  
Configuration And Conformation

Dipole moments of N,N'-diphenylformamidine and its para-halogen derivatives were measured in benzene solution. Since the prototropic rearrangement is degenerate, the dipole moments can be simply interpreted in terms of the E configuration on C=N and a conformational equilibrium on C-N. The two forms, Eap and Esp are populated approximately in the 1 : 1 ratio: the former is the conformation found in the crystal. The dipole moments anticipated for individual conformations were calculated by vectoraddition of bond moments: the previously determined correction for conjugation was found unnecessary.

Hydrogen bonding, configuration and conformation of substituted α-oxo oximes and hydrazones

1979 ◽  
Vol 44 (8) ◽  
pp. 2494-2506 ◽  
Author(s):  
Otto Exner ◽  
Jorga Smolíková ◽  
Václav Jehlička ◽  
Ahmad S. Shawali
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Carbonyl Group ◽  
Intramolecular Hydrogen Bond ◽  
Benzene Solution ◽  
Dipole Moments ◽  
H Nmr ◽  
Intramolecular Hydrogen ◽  
Derivatives Of ◽  
Configuration And Conformation

Substituted 2-bromo-1-phenylglyoxal 2-phenylhydrazones IIIa-f exist in tetrachloromethane or benzene solutions prevailingly in E-configuration and in conformation A with an intramolecular hydrogen bond. The latter was evidenced by the N-H valence frequency at 3 290 cm-1 and by 1H NMR shifts with reference to derivatives without a carbonyl group - α-chlorobenzaldehyde phenylhydrazones V. From dipole moments of IIIa-d, measured in benzene solution, the contribution of the hydrogen bond (μH) was evaluated to 17 . 10-30 C m. This quantity is twice larger than in any other reported compound but the direction of the vector is as usual: approximately from H to N. In structurally similar derivatives of hydroxylamine, substituted 2-phenylglyoxylhydroximoyl chlorides IVa-d, no intramolecular hydrogen bond was detected; the dipole moments found were interpreted in terms of the Z-configuration and the prevailing conformation G.

A Study of d-Orbital Effects in Esters of Trifluorothiolacetic Acid. A Comparison of Evidence from Dipole Moment and Kinetic Data

1974 ◽  
Vol 52 (17) ◽  
pp. 3113-3118 ◽  
Author(s):  
E. Bock ◽  
A. Queen ◽  
S. Brownlee ◽  
T. A. Nour ◽  
M. N. Paddon-Row
Keyword(s):  
Dipole Moment ◽  
Trifluoroacetic Acid ◽  
Kinetic Data ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Aqueous Acetone ◽  
Electron Release ◽  
Hydrolysis Of ◽  
D Orbitals

The dipole moments of a series of esters of trifluoroacetic acid and trifluorothiolacetic acid have been determined in benzene solution at 25 °C. The results are consistent with conjugative and hyperconjugative electron release by the hydrocarbon groups to the d-orbitals of sulfur. This conclusion is supported by data for the hydrolysis of these compounds in water or aqueous acetone.

Dipole moments of some ethylene derivatives

1967 ◽  
Vol 45 (10) ◽  
pp. 1097-1100 ◽  
Author(s):  
E. Bock ◽  
E. F. Dojack
Keyword(s):  
Dipole Moment ◽  
Carbon Tetrachloride ◽  
Solvent Effect ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Vinyl Ketone ◽  
Methyl Vinyl Ketone ◽  
Methyl Vinyl ◽  
Vinyl Bromide ◽  
Reported Data

The dipole moments of the ethylene derivatives acrylonitrile, chloroacrylonitrile, methyl vinyl ketone, vinyl bromide, 1,1-dichloroethylene, and tribromoethylene were determined in benzene solution at 20 °C. The measured dipole moments were corrected for the solvent effect by the method of Looyenga. In addition the applicability of the Looyenga equation for the solvent effect was tested on earlier reported data for 20 different molecules, whose dipole moments were derived from dilute benzene and carbon tetrachloride solutions, respectively. The corrected dipole moment values were compared with earlier corrected values calculated according to the method of Le Fevre and Le Fevre and with reported gas values. It was found that for most compounds both methods of correction yielded dipole moment values which differed by 0–10% from the gas values.

The conformation of aryl carbonates. A dipole moment study

1981 ◽  
Vol 46 (4) ◽  
pp. 856-860 ◽  
Author(s):  
Otto Exner ◽  
Václav Jehlička
Keyword(s):  
Dipole Moment ◽  
Benzene Solution ◽  
Dipole Moments

The dipole moments of diaryl carbonates I-V in benzene solution are consistent with the Z,Z-conformation (A) in which the conformation of simple esters is repeated in the two moieties. The E,Z-form (B) was not detected; it may be either present as a quite small fraction or only with specific, overcrowded structures.

Conformation around several equivalent bonds. Polymethoxy derivatives of benzene

1983 ◽  
Vol 48 (4) ◽  
pp. 1030-1041 ◽  
Author(s):  
Otto Exner ◽  
Václav Jehlička
Keyword(s):  
Dipole Moment ◽  
Crystalline Phase ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Graphical Comparison ◽  
Methoxy Groups ◽  
Derivatives Of

Dipole moments of benzene methoxy derivatives I-IX were measured in benzene solution and discussed in terms of the conformation around the Car-O bonds, exploiting the method of graphical comparison and systematic introduction of substituents. In the case of 1,2-dimethoxybenzene several explanations are in accord with the dipole moment data. However, considering all available evidence, most probable seems to be the presence of two conformers, one of which is non-planar with two non-equivalent methoxy groups (IC). The conformation of 1,2,3-trimethoxybenzene is similar to that found for many derivatives in the crystalline phase (VC), only the outer methoxy groups are probably slightly deviating from the coplanar position.

A physical Study on the Aromaticity of 4H-Pyran-4-one, 9H-Xanthen-9-one, and related sulphur Compounds

1986 ◽  
Vol 41 (10) ◽  
pp. 1250-1257 ◽  
Author(s):  
Henri Lumbroso ◽  
Jacqueline Curé ◽  
Michel Evers
Keyword(s):  
Dipole Moment ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Moment Analysis ◽  
Sulphur Compounds ◽  
Physical Study

Dipole moment analysis of 4H-pyran-4-one and 9H-xanthen-9-one, and their sulphur analogues, and of 9H-selenoxanthen-9-one, enables a discussion on their aromaticities. In the present work, the dipole moments of tetrahydro-4H-pyran-4-one, tetrahydrothio-4H-pyran-4-one, tetrahydroseleno- 4H-pyran-4-one, 9(10H)-anthracen-9-one, 9H-xanthen-9-one, 9H-thioxanthen-9-one and 9H-selenoxanthen-9-one were measured in benzene solution at 30.0 °C.

Dipole moments and conformation of peroxy esters

1981 ◽  
Vol 46 (2) ◽  
pp. 490-497 ◽  
Author(s):  
Božo Plesničar ◽  
Otto Exner
Keyword(s):  
Dipole Moment ◽  
Dihedral Angle ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Ester Group ◽  
Model Compounds ◽  
Tert Butyl ◽  
Butyl Esters

Dipole moments of sixteen substituted peroxybenzoic esters III, IV were measured in benzene solution and interpreted in terms of the conformation around the O-O bond. The dipole moment of the CO3R group is different for R = methyl and R = tert-butyl, viz. 9.0 and 10.4 . 10-30 C m, respectively. Its solution into components was carried out making reference to the dipole moments of substituted benzoic esters as model compounds. As a result the dihedral angle τ = C-O-O-C was estimated to 160-180° in the case of tert-butyl peroxy esters IV and to 110-150° in the case of methyl peroxy esters III. The mesomeric dipole moment expressing the conjugation within the ester group was estimated to 0.8 or 1.5 . 10-30 C m for methyl or tert-butyl esters, respectively.

On the molecular conformation of the bis-1,3-dioxolyl molecule in decahydronaphthalene and benzene solutions

1977 ◽  
Vol 55 (9) ◽  
pp. 1440-1443 ◽  
Author(s):  
Ernst Bock ◽  
Garnette Sutherland ◽  
David McKinnon ◽  
Edward Tomchuk
Keyword(s):  
Dipole Moment ◽  
Temperature Dependence ◽  
Electric Dipole ◽  
Molecular Conformation ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Conformational Behavior ◽  
Electric Dipole Moments ◽  
Solvation Theory

The electric dipole moments of the bis-1,3-dioxolyl molecule were determined in dilute decahydronaphthalene solution at 25 and 100 °C and in dilute benzene solution at 25 °C. From the temperature dependence of the dipole moment it is concluded that the trans rotamer of the molecule is more stable in both solvents than the gauche rotamer by ∼4.5 kJ mol−1. The conformational behavior of the molecule is discussed in terms of a recently proposed solvation theory.

Electric dipole moments of ortho-, meta-, para-, and penta-fluorostyrene molecules

1968 ◽  
Vol 46 (18) ◽  
pp. 2961-2962 ◽  
Author(s):  
E. Bock ◽  
D. Iwacha
Keyword(s):  
Dipole Moment ◽  
Benzene Ring ◽  
Electric Dipole ◽  
Fluorine Atom ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Electric Dipole Moments ◽  
Molecular Dipole ◽  
Molecular Dipole Moment

The dipole moments of ortho-, meta-, para-, and penta-fluorostyrene were determined in dilute benzene solution at 25 °C. It was found that the magnitude of the molecular dipole moment depends on the position of the fluorine atom in the benzene ring.

Conjugation within the oximino group: A semiquantitative estimation

1988 ◽  
Vol 53 (5) ◽  
pp. 1018-1032 ◽  
Author(s):  
Otto Exner ◽  
Václav Jehlička
Keyword(s):  
Dipole Moment ◽  
Bond Order ◽  
Simple Formula ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Bond Lengths ◽  
Group A ◽  
Structural Database ◽  
A Charge ◽  
Bond Character

The n-π conjugation within the oximino group was estimated on the basis of dipole moments and of bond lengths. The dipole moments were measured on oximes I and O-methyloximes II in benzene solution, the C=N and N-O bond lengths were retrieved from the Cambridge Structural Database for all available derivatives. The results differ somewhat in the quantitative sense but can be always interpreted in terms of the classical mesomeric formulae IV ↔ V. This formalism postulates – in agreement with experiments – a lowered C=N bond order, some double bond character of the N-O bond, planarity of the C=NOR group, and an excess dipole moment (μm) oriented in the sense of a charge transfer from O toward C. Quite different results were obtained for O-acetyloximes III. While their bond lengths could agree with a weakened conjugation, the excess dipole moment is oriented from C towards O and cannot be expressed by any simple formula. Hence the mesomeric formulae may represent an acceptable description of the actual charge distribution in many cases but not in all.

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