Acetyl group relaxation in four aromatic ketones

1977 ◽  
Vol 55 (4) ◽  
pp. 583-587 ◽  
Author(s):  
C. K. McLellan ◽  
S. Walker
Keyword(s):  
Energy Barrier ◽  
Benzene Solution ◽  
Far Infrared ◽  
Aromatic Ketones ◽  
Dielectric Absorption ◽  
Nmr Data ◽  
Polystyrene Matrix ◽  
Absorption Studies ◽  
Acetyl Group ◽  
Experimental Errors

Dielectric absorption studies have been made of group relaxation of acetophenone, 1,4-diacetylbenzene,4-acetylbiphenyl, and 2-acetylfluorene in a polystyrene matrix, and two rigid molecules have also been examined. For acetyl group relaxation in acetophenone, ΔHE = 29.6 ± 0.6 kJ mol−1 and ΔSE = 26 ± 3 JK−1 mol−1 (95% confidence intervals). The energy barrier for acetyl group relaxation is of the same order as that obtained from nmr data. Our results for acetophenone differ appreciably from the values reported for the gaseous phase by the far-infrared approach and from those by the dielectric absorption of aromatic ketones in benzene solution. The enthalpies of activation for acetyl group relaxation in 1,4-diacetylbenzene, 4-acetylbiphenyl, and 2-acetylfluorene are 29, 30, and 32 kJ mol−1, respectively, which values are identical within their experimental errors. These three substances have also been examined as pure solids, yielding enthalpies of activation for acetyl group relaxation of a similar magnitude.

Activation energy for methoxy group relaxation

1978 ◽  
Vol 56 (13) ◽  
pp. 1800-1803 ◽  
Author(s):  
M. A. Mazid ◽  
J. P. Shukla ◽  
S. Walker
Keyword(s):  
Activation Energy ◽  
Aromatic Ring ◽  
Energy Barrier ◽  
Methoxy Group ◽  
Steric Effects ◽  
Molecular Process ◽  
Dielectric Absorption ◽  
Polystyrene Matrix ◽  
Absorption Studies ◽  
Methoxy Groups

Dielectric absorption studies hove been made on seven compounds which hove methoxy groups attached to an aromatic ring and on some related rigid molecules. The solutes hove been dispersed in a polystyrene matrix. In some cases, the absorptions due to the group and the molecular process have been separated completely, and this has permitted the estimation of more accurate Eyring enthalpies of activation for methoxy group relaxation. These values hove been compared with those in the literature and, on the whole, it would seem likely that the energy barrier to group relaxation is small and of the order of 10 kJ mol−1 for cases where there is no mutual conjugation or steric effects.

Dielectric absorption of a few aromatic amines in a polystyrene matrix

1981 ◽  
Vol 59 (2) ◽  
pp. 232-237 ◽  
Author(s):  
S. P. Tay ◽  
S. Walker
Keyword(s):  
Aromatic Amines ◽  
Amino Group ◽  
Torsional Barrier ◽  
Dielectric Absorption ◽  
Enthalpy Of Activation ◽  
Polystyrene Matrix ◽  
Absorption Studies ◽  
Intramolecular Process ◽  
Nitrogen Bond

Dielectric absorption studies in the ranges 77–373 K and 102–107 Hz have been made on aniline, poly(4-aminostyrene), p-toluidine, 4-chloroaniline, 1-aminopyrene, and 4-aminobiphenyl in a polystyrene matrix. An intramolecular process has been observed in poly(4-aminostyrene) and 1-aminopyrene with enthalpies of activation of 25 and 26 kJ mol−1 respectively. The enthalpy of activation of the intramolecular process is of the same order as that found for the torsional barrier in aniline and 4-fluoroaniline. The most likely candidate for the intramolecular process appears to be rotation of the amino group about the carbon–nitrogen bond.

Molecular and group relaxation studies in parasubstituted benzenes in various media

1979 ◽  
Vol 57 (21) ◽  
pp. 2843-2847 ◽  
Author(s):  
J. Crossley ◽  
J. P. Shukla ◽  
S. P. Tay ◽  
M. S. Walker ◽  
S. Walker
Keyword(s):  
Group Process ◽  
Activation Enthalpy ◽  
Small Contribution ◽  
Molecular Processes ◽  
Dielectric Absorption ◽  
Polystyrene Matrix ◽  
Absorption Studies ◽  
The Matrix ◽  
Intramolecular Motion ◽  
Relaxation Studies

Dielectric absorption studies have been made on molecules of the type [Formula: see text][Formula: see text] where X—Y is —OCH3, —COCH3, —CH2Cl, and —CH2CN. The molecules have been dissolved in (a) a polystyrene matrix and (b) in the viscous liquid o-terphenyl. For 1,4-dimethoxybenzene the group process dominates in both media, and estimates have been made of the activation enthalpy for group relaxation. For 1,4-dimethoxybenzene in benzene, decalin, Nujol, and o-terphenyl solutions, however, there appears to be a small contribution from the molecular process. No such contribution was detected in the matrix studies on this solute molecule. For 1,4-diacetylbenzene, 1,4-bis(chloromethyl)benzene, and 1,4-bis(cyanomethyl)benzene in o-terphenyl solution it again seems that the group and molecular processes overlap. However, in polystyrene the enthalpies of activation which emerge are characteristic of the group relaxation process as determined by the nmr approach. Altogether, the work illustrates that o-terphenyl may be a useful solvent in helping to decide whether a solute has contributions from an intramolecular motion.

Dielectric relaxation in 2-acetylnaphthalene and related compounds

1978 ◽  
Vol 56 (4) ◽  
pp. 567-573 ◽  
Author(s):  
J. Crossley ◽  
M. A. Mazid ◽  
C. K. McLellan ◽  
P. F. Mountain ◽  
S. Walker
Keyword(s):  
Activation Parameters ◽  
Low Frequencies ◽  
Microwave Frequencies ◽  
Dielectric Absorption ◽  
Free Energy Of Activation ◽  
Polystyrene Matrix ◽  
The Matrix ◽  
Acetyl Group ◽  
Related Compounds ◽  
Xylene Solution

The dielectric absorption of 2-acetylnaphthalene and 2- and 3-acetylphenanthrene has been studied in p-xylene solution at several microwave frequencies and in a polystyrene matrix at low frequencies. Acetyl group relaxation has been established from both sets of data. A clear separation of the dielectric absorption of the molecule and the group has been achieved for both 2- and 3-acetylphenanthrene in the matrix. The Eyring activation parameters have been established for acetyl relaxation in these molecules in the matrix. The free energy of activation values for group relaxation increase in the sequence acetophenone < 2-acetylphenanthrene < 3-acetylphenanthrene < 2-acetylnaphthalene. For the p-xylene solution data the weight factor for group relaxation, C2, is appreciably lower than the theoretical value, so that C2 < C1, bearing out the findings of Fong and Smyth for 2-acetylnaphthalene. In polystyrene matrices, the data for 2- and 3-acetylphenanthrene also indicated that C2 < C1. The enthalpy of activation for acetyl relaxation in 2- and 3-acetylphenanthrene is similar to that for acetophenone and 1,4-diacetylbenzene whereas that for 2-acetylnaphthalene would seem somewhat larger.

LIGHT ABSORPTION STUDIES: PART XII. ULTRAVIOLET ABSORPTION SPECTRA OF BENZALDEHYDES

1958 ◽  
Vol 36 (10) ◽  
pp. 1362-1370 ◽  
Author(s):  
J. C. Dearden ◽  
W. F. Forbes
Keyword(s):  
Absorption Spectra ◽  
Light Absorption ◽  
Electronic Spectra ◽  
Spectral Properties ◽  
Ultraviolet Absorption ◽  
Benzene Derivatives ◽  
Formyl Group ◽  
Steric Interactions ◽  
Absorption Studies ◽  
Acetyl Group

The electronic spectra of benzaldehydes in the region 220–360 mμ are recorded and discussed in terms of previously stated hypotheses. The formyl group is shown to endow benzene derivatives with spectral properties similar to those of the acetyl group in acetophenones, except that steric interactions are slightly modified.

Perfluoroalkyl- and fluoroalkyl- complexes of rhodium(III)

1976 ◽  
Vol 54 (13) ◽  
pp. 2077-2084 ◽  
Author(s):  
Howard C. Clark ◽  
Kenneth J. Reimer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Infrared Spectra ◽  
Oxidative Addition ◽  
Far Infrared ◽  
Addition Reactions ◽  
Nmr Data ◽  
Far Infrared Spectra ◽  
Nuclear Magnetic

A series of perfluoroalkyl (Rf—) and fluoroalkyl (RfCH2—) complexes of rhodium(III) have been prepared by oxidative addition reactions of RfI and RfCH2I (Rf = CF3, C2F5 and C3F7) with trans-RhClCO(PMe2Ph)2. The reaction of CF3I with trans-RhClCO(PMePH2)2 gave RhClI(CF3)CO(PMePh2)2 but no reaction was observed with CF3CH2I. The trans stereochemistry of addition has been assigned to all complexes by nuclear magnetic resonance measurements and the comparison of the far-infrared spectra to those of some bromo compounds: RhBrI(CF3)CO(PMe2Ph)2 and RhBrI(C3F7CH2)CO(PMe2Ph)2. Both 1H and 19F nmr data are presented and discussed.

Dielectric Relaxation of Pyridine in Benzene Solution from Microwave Absorption Studies

2005 ◽  
Vol 219 (10_2005) ◽  
pp. 1431-1436 ◽  
Author(s):  
Sandeep Kumar ◽  
D.R. Sharma ◽  
N. Thakur ◽  
V. S. Rangra ◽  
N.S Negi
Keyword(s):  
Dielectric Relaxation ◽  
Microwave Absorption ◽  
Benzene Solution ◽  
Absorption Studies

Azaborolyl-Komplexe, 27 / Azaborolyl Complexes, 27

1992 ◽  
Vol 47 (5) ◽  
pp. 635-639 ◽  
Author(s):  
Günter Schmid ◽  
Wolfgang Meyer-Zaika
Keyword(s):  
Mass Spectrometry ◽  
Benzene Solution ◽  
Stable Complex ◽  
Intramolecular Rearrangement ◽  
The Novel ◽  
Intramolecular Coordination ◽  
Tert Butyl ◽  
Nmr Data ◽  
Stereoselective Reactions ◽  
Ab Ring

Alkenyl substituted 1H-1,2-azaborolyl (Ab) complexes are promising candidates for stereoselective reactions, due to the chirality of the AbM moiety and the intramolecular coordination of the alkenyl group to the metal atom. The synthesis of [1-tert-butyl-2-methy1-3-(4-penten- l -y1)-η5-1H-1,2-azaborolyl]-bis(triphenylphosphine)rhodium (3) is achieved by the reaction of AbLi (2) [from AbH (1)] with (Ph3P)3RhCl. In benzene solution one PPh3 ligand of 3 is substituted by the C=C group of the pentenyl substituent. Simultaneously the η5-coordination of the Ab ring changes to an allylic η3-coordination forming 4. Steric reasons seem to be responsible for this intramolecular rearrangement. The shorter 2-propen-1-yl substituent is unable to act in the same way and therefore only forms the stable complex [1-tert-butyl-2-methyl-3-(2-propen- l -yl)-η5-1H-1,2-azaborolyl]-bis(triphenylphosphine)rhodium (7). Mass spectrometry, 1H, 11B and 31P NMR data were used to characterize the novel complexes.

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