1H nmr study on substituent effect in hetroelement-containing propynals on the Host–guest complexation with β-cyclodextrin
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Proton NMR
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Dual substituent parameter and dual substituent parameter–non-linear resonances analysis have been successfully applied to model the long-range substituent effect on 13C substituent chemical shifts (SCS) in eight series of β-substituted styrenes, each carrying a nitrile group in the β-position. Different blends of polar and mesomeric effects at various sites were successfully accounted for.
Chemical shift
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Abstract The substituent effect in 1‐, 2‐, and 9‐anthrols is studied by means of B3LYP/6‐311++G(d,p) computation, taking into account substituents (X): NO 2 , CN, OH and NH 2 located in all positions except the adjacent ones. The substituent effect is characterized by approaches based on quantum chemistry: The charge of the substituent active region (cSAR), substituent effect stabilization energy (SESE) and the charge flow index (CFI) describing flow of the charge from X to the fixed group (or vice versa) as well as substituent constants σ . Changes in properties observed in the fixed group (OH) are described by cSAR(OH). Mutual interdependences are found between these descriptors. The HOMA index is used to describe an effect of a substituent on aromaticity of an anthrol hydrocarbon skeleton and of individual rings. In all cases, the classical (influence of X on the properties of OH) and reverse (influence of OH on the properties of X) substituent effects are studied. The latter is clearly documented by the cSAR approach.
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Acceptor
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Methylene
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Proton NMR
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Abstract Ring and ester proton chemical shifts in six series of substituted methyl pyridinecarboxylates have been measured. Results for ring protons ortho and para to the substituent can generally be accounted for by additive substituent, ester and nitrogen effects. Shifts for protons meta to the substituent, when compared with analogous shifts in monosubstituted benzenes, provide evidence of substituent–nitrogen interactions. In particular, a special effect is noted for series where both the proton and substituent are adjacent to the nitrogen. The origin of this effect is discussed. The ester proton results lead to essentially the same conclusions. Although this probe is much less sensitive to substituent effects, the same special effect is evident for the methyl 6‐X‐picolinate series.
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The acidities of several substituted phenoltricarbonylchromium compounds have been determined in 50% ethanol. A plot of pKa values versus Hammett substituent constants indicates that no distortion of substituent effects occurs upon complexation of an aromatic system to the tricarbonylchromium moiety.
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Abstract Additivity of substituent effects in the methyl-triphenylphosphonium system with substituents on different phenyl groups is tested. Results show that additive linear free energy relationships can be applied to describe multiple substituent effects in this system.
Additive function
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