Effect of substituents on the 1H-NMR chemical shifts of 3-methylene-2-substituted-1,4-pentadienes

The principle of linear free energy relationships was applied to the 1H chemical shifts of the b-vinyl proton atoms of 3-methylene-2-substituted-1,4-pentadienes. The correlations of the proton chemical shifts with Swain and Lupton substituent parameters provide a mutually consistent picture of the electronic effects in these compounds. The overall pattern of proton chemical shifts can be largely accounted for by a model of substituent effects based on field, resonance and p polarization effects. Owing to the particular geometric arrangement of the vinyl group in 3-methylene-2-substituted-1,4-pentadienes, the b-vinyl protons HB and HC have different sensitivities to polar and resonance effects. The different sensitivities of the 1H chemical shifts to resonance effects reveals some effects not predicted by the model outlined above. Evidence is presented that demonstrates that both the 1H and 13C chemical shifts for these compounds reflect their ground-state charge densities

Synthesis and investigation of solvent effects on the ultraviolet absorption spectra of 5-substituted-4-methyl-3-cyano-6-hydroxy-2-pyridones

A number of 5-substituted-4-methyl-3-cyano-6-hydroxy-2-pyridones from cyanoacetamide and the corresponding alkyl ethyl acetoacetates were synthesized according to modified literature procedures. The alkyl ethyl acetoacetates were obtained by the reaction of C-alkylation of ethyl acetoacetate. An investigation of the reaction conditions for the synthesis of 4-methyl-3-cyano-6-hydroxy-2-pyridone from cyanoacetamide and ethyl acetoacetate in eight different solvents was also performed. The ultraviolet absorption spectra of synthesized pyridones were measured in nine different solvents in the range 200400 nm. The effects of solvent polarity and hydrogen bonding on the absorption spectra are interpreted by means of linear solvation energy relationships using a general equation of the form n = n0 + sp* + aa + bb, where p* is a measure of the solvent polarity, a is the scale of the solvent hydrogen bond donor acidities and b is the scale of the solvent hydrogen bond acceptor basicities

Substituent and solvent effects on the UV/vis absorption spectra of 3-<i>N</i>-alkyl-5-carboxy uracils

1137-1140Absorption spectra of ten 3-N-alkyl-5-carboxy uracils are recorded in fourteen solvents in the range 200-400 nm. The absorption frequencies of carboxy carbonyl electronic transitions are correlated by dual substituent parameter (DSP) treatment involving both polar (σ*) and steric (Es or vc) substituent constants. The effect of solvent polarity and solvent/solute hydrogen bonding interactions on the absorption spectra are interpreted by means of linear solvation energy relationships (LSER) using a general equation of the form v = vo + sπ* + bβ + aα where π* is a measure of the solvent polarity, β is the scale of the solvent hydrogen bond acceptor basicities and a is the scale of the solvent hydrogen bond donor acidities

Effect of substituents on the 13C-NMR chemical shifts of 3-methylene-4-substituted-1,4-pentadienes. Part I.

The principles of linear free energy relationships were applied to the 13C substituent chemical shifts (SCS) of the carbon atoms in the unsaturated chain of 3-methylene-4-substituted-1,4-pentadienes. Correlations of the SCS with the substituent parameters of Swain and Lupton provide a mutually consistent picture of the electronic effects in these compounds. The pattern of the electronic effects can be fully rationalized by a model based on the direct transmission of substituent effects through-space (direct through-space field effects), and via conjugative interactions (resonance effects), or by substituent-induced polarization of the p-system in the unsaturated chain (p-polarization effect). Semi-empirical MNDO-PM3 calculations suggest the s-cis conformation of 3-methylene-4-substituted-1,4- -pentadienes as the one with minimal heat of formation