13C NMR study of 7,7-disubstituted quinone methides

1981 ◽  
Vol 46 (9) ◽  
pp. 2083-2090 ◽  
Author(s):  
Antonín Lyčka ◽  
Dobroslav Šnobl ◽  
Bohumír Koutek ◽  
Libuše Pavlíčková ◽  
Milan Souček
Keyword(s):  
Double Bond ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Exocyclic Double Bond ◽  
Carbonyl Carbon Atom ◽  
Resonance Contribution ◽  
Carbonyl Carbon ◽  
Quinone Methides ◽  
Total Transmission ◽  
Nmr Study

Carbon-13 chemical shift assignments for nine 7,7-disubstituted 2,6-ditert-butylquinone methides of the types III-VI are reported. The 13C shifts of the exocyclic double bond carbon atoms are extraordinarily sensitive to C(7) substitution, viz. ΔδC(7) = 82.4 ppm and ΔδC(4) = 56.7 ppm on going from the dimethylamino to the cyano substituent. In contrast, electronic properties of the substituents are only weakly expressed on the carbonyl carbon atom. Satisfactory Swain-Lupton correlations were found for C(1), C(2) and C(4) chemical shifts yielding more than 50% of resonance contribution to the total transmission of substituent effects. Intercorrelations between the exocyclic double bond carbon chemical shifts of quinone methides and of identically substituted fulvenes as well as styrenes are also presented.

13C NMR study of substituted quinone methides. 2- and 2,6-substituted fuchsones

1981 ◽  
Vol 46 (8) ◽  
pp. 1775-1787 ◽  
Author(s):  
Antonín Lyčka ◽  
Dobroslav Šnobl ◽  
Bohumír Koutek ◽  
Libuše Pavlíčková ◽  
Milan Souček
Keyword(s):  
13C Nmr ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Coupling Constants ◽  
Quinone Methides ◽  
Nmr Study ◽  
Related Compounds

Carbon-13 chemical shifts and 1J(CH) coupling constants for 11 fuchsones of the types I and II in deuteriochloroform are reported. The assignments are based on an analysis of proton coupled and proton decoupled spectra and on the analogy to chemical shifts of some structuraly related compounds. Satisfactory Swain-Lupton F and R correlations which were found for most of 13C chemical shifts afforded values for percent resonance contributions to transmission of substituent effects as follows, C(1), 19%; C(3), 71%; C(7), 43%. Some alternative correlations for other similar systems e.g. quinones and tropones are also given.

13C NMR study of 3-(X-benzal)phthalides and 2-(X-benzal)-1,3-indanediones

1980 ◽  
Vol 45 (10) ◽  
pp. 2772-2778 ◽  
Author(s):  
Eva Solčániová ◽  
Pavol Hrnčiar ◽  
Tibor Liptaj
Keyword(s):  
Chemical Shift ◽  
Nmr Spectra ◽  
Electronic Effect ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Carbonyl Groups ◽  
Aryl Group ◽  
Nmr Study ◽  
Derivatives Of ◽  
C Nmr

13C NMR spectra of 14 derivatives of 3-(X-benzal)phthalides (I) and 10 derivatives of 2-(X-benzal)-1,3-indanediones (II) were investigated. The correlation of 13C chemical shifts of carbon atoms of the phthalide ring with σ-constants showed that the electronic effect of substituents was transmitted from the benzylidene group of 3-(X-benzal)phthalides on the chemical shift of the carbonyl group not only through oxygen, but also through the aromatic ring of the phthalide moiety. The transmission of substituent effects in 2-(X-benzal)-1,3-indanediones on the chemical shift of the carbonyl groups was more pronounced on the carbonyl, which is in the trans-arrangement with respect to the aryl group. This phenomenon was also observed at carbon atoms of the benzene ring of the indanedione moiety closer to the trans-CO group.

13C NMR spectra and substituent effects of meta and para substituted benzoyl isothiocyanates

1985 ◽  
Vol 50 (6) ◽  
pp. 1422-1431 ◽  
Author(s):  
Ivan Danihel ◽  
Ján Imrich ◽  
Dušan Košťík ◽  
Pavol Kristian ◽  
Gabriela Barančíková
Keyword(s):  
Carbon Atom ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Carbonyl Carbon Atom ◽  
Benzene Nucleus ◽  
Benzoyl Isothiocyanates ◽  
Benzoyl Chlorides ◽  
Parameter Approach ◽  
C Nmr

13C NMR spectra have been studied of 20 meta and para substituted benzoyl isothiocyanates and corresponding benzoyl chlorides. The 13C SCS values of the carbon atom in NCS group have been found to correlate linearly with the Hammet σm,p constants of the substituents as well as with the corresponding π electron charges. The 13C SCS (substituent chemical shift) values of the carbonyl carbon atom of the compounds investigated are little sensitive to substituent effects and are analyzed on the basis of the dual-substituent-parameter approach. Also discussed are the intercorrelation relations of the 13C SCS values of benzoyl isothiocyanates and phenyl isothiocyanates and substituent effects on chemical shifts of carbon atoms of the benzene nucleus. For the benzoyl isothiocyanates the 13C NMR increments of chemical shifts and σm,p substituent constants of CONCS group have been determined.

scholarly journals Reactive intermediates. Some chemistry of quinone methides

2000 ◽  
Vol 72 (12) ◽  
pp. 2299-2308 ◽  
Author(s):  
Y. Chiang ◽  
A. J. Kresge ◽  
Y. Zhu
Keyword(s):  
Acid Catalysis ◽  
Isotope Effects ◽  
Reactive Intermediates ◽  
Quinone Methide ◽  
Carbonyl Carbon Atom ◽  
Carbonyl Carbon ◽  
Quinone Methides ◽  
Rate Determining Step ◽  
Energy Relationships ◽  
Acid Catalyzed

Quinone methides were produced in aqueous solution by photochemical dehydration of o-hydroxybenzyl alcohols (o-HOC6H4CHROH; R = H, C6H5, 4-CH3OC6H4), and flash photolytic techniques were used to examine their rehydration back to starting substrate as well as their interaction with bromide and thiocyanate ions. These reactions are acid-catalyzed and show inverse isotope effects (kH+/kD+ < 1), indicating that they occur through preequilibrium protonation of the quinone methide on its carbonyl carbon atom followed by rate-determining capture of the benzyl carbocations so formed by H2O, Br-, or SCN-. With some quinone methides (R = C6H5 and 4-CH3OC6H4) this acid catalysis could be saturated, and analysis of the data obtained in the region of saturation for the example with R = 4-CH3OC6H4 produced both the equilibrium constant for the substrate protonation step and the rate constant for the rate-determining step. Energy relationships comparing the quinone methides with their benzyl alcohol precursors are derived.

17O NMR study of ortho and alkyl substituent effects in substituted phenyl and alkyl esters of benzoic acids

2011 ◽  
Vol 76 (12) ◽  
pp. 1737-1763 ◽  
Author(s):  
Vilve Nummert ◽  
Vahur Mäemets ◽  
Mare Piirsalu ◽  
Signe Vahur ◽  
Ilmar A. Koppel
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Alkyl Substituent ◽  
Ester Group ◽  
Carbonyl Oxygen ◽  
Steric Interaction ◽  
Alkyl Esters ◽  
17O Nmr ◽  
Nmr Study ◽  
Substituent Constants

17O NMR spectra for 44 ortho-, meta- and para-substituted phenyl and alkyl benzoates (C6H5CO2C6H4-X, C6H5CO2R) at natural abundance in acetonitrile were recorded. Substituent effects on the 17O NMR chemical shifts, δ(17O), of the carbonyl oxygen and the single-bonded phenoxy (OPh) and alkoxy (OR) oxygens have been studied. The δ(17O) values of the carbonyl oxygen for para derivatives showed a good correlation with the σ° constants. The δ(17O) values of carbonyl oxygen for ortho derivatives were found to be described well with the Charton equation containing the inductive, σI, resonance, σ°R, and steric, EsB, substituent constants in case the data treatment was performed separately for electron-donating +R and electron-attracting –R substituents. The electron-donating +R ortho and para substituents in substituted benzoates caused shielding and the electron-withdrawing –R substituents produced deshielding of the O signal. The steric interaction of ortho substituents with the ester group decreased the electron density at the carbonyl oxygen. In alkyl benzoates the δ(17O) values were found to be described well with the inductive, σI, and the steric, EsB, substituent constants.

13C and 1H nuclear magnetic resonance spectroscopy of C-19 and 6β-methyl substituted steroids: long-range shift effects in conformational analysis

1979 ◽  
Vol 57 (1) ◽  
pp. 27-37 ◽  
Author(s):  
Katherine Násfay Scott ◽  
Thomas Harold Mareci
Keyword(s):  
Double Bond ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Preferred Orientation ◽  
Range Shift ◽  
Resonance Spectroscopy ◽  
Relative Stabilities ◽  
H Nmr ◽  
1H Nuclear Magnetic Resonance

13C and 1H nmr spectra were obtained and assigned for nine C-19 substituted cholest-5-enes, three 6β-substituted 19-norcholest-5(10)-enes, and several related steroids. 13C chemical shift effects have previously not been studied in either C-19 substituted steroids or in cholest-5(10)-enes. In the present study, substituent effects on the 13C chemical shifts of the α, β, γ, and δ carbons were evaluated in detail. Although the substituent in C-19 substituted and 6β-methyl substituted steroids is less rigidly oriented with respect to the rest of the molecule than in ring-substituted steroids, similar shift effects were observed. In cholest-5-enes the observed 13C and 1H shift effects and the temperature dependence of the 13C shifts indicate that the preferred orientation of the C-19 substituent is anti to C-1. The relative stabilities of the rotamers can be attributed to the orientation of the C-19 substituent with respect to the double bond. This interpretation is supported by the fact that the preferred orientation of the iodine in 6β-iodomethyl-19-norcholest-5(10)-en-3β-ol has the same spacial relationship with respect to the double bond, i.e., gauche to C-5 and C-7.

Some Considerations Regarding the 1H and 13C Spectra of 4-(1-azulenyl)-2,6-bis(2-heteroaryl-vinyl)- pyrylium and Pyridinium and their Corresponding Pyridines

2018 ◽  
Vol 69 (1) ◽  
pp. 64-69
Author(s):  
Liviu Birzan ◽  
Mihaela Cristea ◽  
Constantin C. Draghici ◽  
Alexandru C. Razus
Keyword(s):  
Double Bond ◽  
13C Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Pyridinium Salts ◽  
13C Nmr Spectra ◽  
1H And 13C Nmr ◽  
Pyrylium Salts

The 1H and 13C NMR spectra of several 2,6-diheteroarylvinyl heterocycles containing 4-azulenyl moiety were recorded and their proton and carbon chemical shifts were compared with those of the compounds without double bond between the heterocycles. The influence of the nature of central and side heterocycles, molecule polarization and anisotropic effects were revealed. The highest chemical shifts were recorded for the pyrylium salts and the lowest at pyridines, but in the case of the pyridinium salts, the protons chemical shifts at the central heterocycle are more shielded due to a peculiar anisotropy of the attached vinyl groups.

Sign in / Sign up

Export Citation Format

Share Document