The synthesis, characterization, and thermal isomerization of some 1,1,2,2-tetraarylcyclopropanes

1982 ◽  
Vol 60 (18) ◽  
pp. 2313-2320 ◽  
Author(s):  
Donald R. Arnold ◽  
Danial D. M. Wayner ◽  
Masato Yoshida
Keyword(s):  
Transition State ◽  
Chemical Shifts ◽  
Thermal Isomerization ◽  
Spectral Characterization ◽  
Arrhenius Parameters ◽  
Cis And Trans

The synthesis and spectral characterization of an extensive series of 1,1,2,2-tetraarylcyclopropanes are reported. The effects of substituents on the 13Cmr and 1Hmr chemical shifts are examined in detail. In a series of symmetrically substituted derivatives, the, 13Cmr chemical shifts correlate with ΣσR0. This correlation is only observed in cases where the Cα—Cβ bond has no net polarity. Details of the thermal isomerization of those derivatives for which the possibility of cis and trans configurations exists are also reported. Trends in the Arrhenius parameters provide evidence for the biradical character of the transition state. Other data supporting the biradical character of the transition state are discussed.

Merostabilization in radical ions, triplets, and biradicals. 5. The thermal cis–trans isomerization of para-substituted tetraphenylethylenes

1981 ◽  
Vol 59 (3) ◽  
pp. 609-620 ◽  
Author(s):  
William J. Leigh ◽  
Donald R. Arnold
Keyword(s):  
Transition State ◽  
Benzene Solution ◽  
Substituent Effects ◽  
Thermal Isomerization ◽  
Radical Ions ◽  
Trans Isomers ◽  
X Ray ◽  
System A ◽  
Cis And Trans Isomers ◽  
Cis And Trans

The cis- and trans-isomers of four para-substituted (three disubstituted and one tetrasubstituted) tetraphenylethylenes have been synthesized, separated, and characterized by either dipole moment or X-ray analysis. The rates of thermal isomerization of the disubstituted derivatives in benzene solution correlate with a substituent parameter reflecting substituent effects on benzylic radical stabilities (σ•), which reflects the biradical nature of the transition state for thermal isomerization in this system. A significant rate enhancement is observed for the tetrasubstituted derivative, in which merostabilization of the transition state is possible.The Arrhenius parameters for thermal isomerization in benzene were determined. From the variation observed for the disubstituted derivatives, an estimate of 35.5 kcal mol−1 for the rotational barrier in tetraphenylethylene is obtained. The activation energy for thermal isomerization of the tetrasubstituted derivative is 2 kcal mol−1 lower than those of the other three; this provides an assessment of the importance of merostabilization in this system.The thermal isomerization of some related olefins (e.g. bianthrylidenes and indigo derivatives) is discussed in light of these results.

The thermal isomerization of 1. 2-dimethyl cyclo propane II. Structural isomerization

1961 ◽  
Vol 260 (1302) ◽  
pp. 424-432 ◽  
Keyword(s):  
Transition State ◽  
Thermal Isomerization ◽  
Reaction Vessel ◽  
Rate Equations ◽  
Arrhenius Parameters ◽  
Temperature Range ◽  
Structural Isomerization ◽  
Electronic Integration ◽  
Ring Transition State

This isomerization has been investigated between 434 and 475 °C. In this temperature range, in an ‘aged’ reaction vessel, the structural isomerization from either cis or trans 1. 2-dimethyl cyclo propane occurs as a unimolecular transformation which is slower than the reversible cis-trans isomerization. The products of the reaction are 2-methylbut-1-ene, 2-methylbut-2-ene and cis and trans pent-2-ene. The rates of formation of these compounds have been measured and the Arrhenius parameters evaluated. The rate equations for the formation of 2-methylbut-1-ene and 2-methylbut-2-ene are k ∞ = 10 13.93 exp(-61900/ RT ) S -1 and 10 14.08 exp (-62300/ RT ) S -1 respectively and are the same for their production from either the cis or the trans dimethyl cyclo propane. The pent-2-enes are formed more rapidly from cis 1. 2-dimethy cyclo propane than from the trans compound. From cis 1.2-dimethyl cyclo propane cis and trans pent-2-ene are formed at rates given by the equations k ∞ = 10 13.92 exp (-61400/ RT )s -1 and 10 13.96 exp (-61200/ RT )s -1 , respectively. From trans 1.2-dimethyl cyclo propane the rate equations are k ∞ = 10 14.40 exp (-63600/ RT )s -1 and 10 14.30 exp (-62900/ RT )s -1 . The possible mechanisms for both the geometrical and structural isomerizations have been discussed and it has been concluded than an ‘expanded ring’ transition state gives a satis­factory explanation of the results obtained. It is also suggested that this strengthens the case for a similar mechanism in the case of the isomerization of cyclo propane. Gas chromato­graphy, by means of a katharometer detector with electronic integration, has been used throughout and has been developed to give a precision of ±0.5% in the analysis of the reaction mixtures.

Optimized Synthesis and Spectral Characterization of Some Hydrazones Based on 5-Nitroindazole with Pharmacological Potential

2014 ◽  
Vol 59 (3) ◽  
pp. 313-318
Author(s):  
C. Cheptea ◽  
◽  
L.M. Ivan ◽  
D.O. Dorohoi ◽  
V. Sunel ◽  
...  
Keyword(s):  
Spectral Characterization ◽  
Pharmacological Potential

Synthesis and Spectral Characterization of Derivatives of Benzotriazole and Piperidine

2018 ◽  
Vol 8 (2) ◽  
pp. 278-287
Author(s):  
Selvarathy Grace P ◽  
Ravindran Durainayagam B ◽  
Pon Matheswari P.
Keyword(s):  
Spectral Characterization ◽  
Derivatives Of

Synthesis and Spectral Characterization of New S-Alkylated 1,2,4-Triazoles as Potential Biological Agents

2017 ◽  
Vol 68 (10) ◽  
pp. 2436-2439
Author(s):  
Stefania Felicia Barbuceanu ◽  
Laura Ileana Socea ◽  
Constantin Draghici ◽  
Elena Mihaela Pahontu ◽  
Theodora Venera Apostol ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Spectral Data ◽  
1H Nmr ◽  
Elemental Analysis ◽  
13C Nmr ◽  
Ethyl Bromide ◽  
Spectral Characterization ◽  
Basic Medium ◽  
Phenacyl Bromide

In the work we presented the behavior of 5-(4-(4-X-phenylsulfonyl)phenyl)-4-(n-propyl)-2H-1,2,4-triazole-3(4H)-thiones (X= Cl or Br) with some alkylation agents. Thus, new S-alkylated 1,2,4-triazole derivatives were synthesized by reaction of the corresponding 1,2,4-triazole-3-thione derivatives with different �-halogenated compounds (ethyl bromide, ethyl chloroacetate or phenacyl bromide), in basic medium. The structures of synthesized compounds were elucidated by spectral data (1H-NMR, 13C-NMR, mass spectrometry) and elemental analysis.

Synthesis and characterization of a series of 1-methyl-4-[2-aryl-1-diazenyl]piperazines and a series of ethyl 4-[2-aryl-1-diazenyl]-1-piperazinecarboxylates

2004 ◽  
Vol 82 (8) ◽  
pp. 1294-1303 ◽  
Author(s):  
Vanessa Renée Little ◽  
Keith Vaughan
Keyword(s):  
Free Energy ◽  
Chemical Shifts ◽  
Linear Free Energy Relationship ◽  
Piperazine Ring ◽  
Linear Free Energy ◽  
In Series ◽  
Methylene Groups ◽  
Diazonium Coupling ◽  
The Difference

1-Methylpiperazine was coupled with a series of diazonium salts to afford the 1-methyl-4-[2-aryl-1-diazenyl]piperazines (2), a new series of triazenes, which have been characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, and elemental analysis. Assignment of the chemical shifts to specific protons and carbons in the piperazine ring was facilitated by comparison with the chemical shifts in the model compounds piperazine and 1-methylpiperazine and by a HETCOR experiment with the p-tolyl derivative (2i). A DEPT experiment with 1-methylpiperazine (6) was necessary to distinguish the methyl and methylene groups in 6, and a HETCOR spectrum of 6 enabled the correlation of proton and carbon chemical shifts. Line broadening of the signals from the ring methylene protons is attributed to restricted rotation around the N2-N3 bond of the triazene moiety in 2. The second series of triazenes, the ethyl 4-[2-phenyl-1-diazenyl]-1-piperazinecarboxylates (3), have been prepared by similar diazonium coupling to ethyl 1-piperazinecarboxylate and were similarly characterized. The chemical shifts of the piperazine ring protons are much closer together in series 3 than in series 2, resulting in distortion of the multiplets for these methylenes. It was noticed that the difference between these chemical shifts in 3 exhibited a linear free energy relationship with the Hammett substituent constants for the substituents in the aryl ring. Key words: triazene, piperazine, diazonium coupling, NMR, HETCOR, linear free energy relationship.

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