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The Substituent Effect of 1‐Arylazonaphthen‐2‐ols on Azo‐hydrazone Tautomerization According to NMR Analysis
Author(s) -
Lin YiCang,
Chen ChienChih,
Ding MeiFan,
Lin ShawTao
Publication year - 2015
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.201400381
Subject(s) - substituent , hydrazone , chemistry , tautomer , chemical shift , computational chemistry , hammett equation , proton nmr , carbon 13 nmr , stereochemistry , reaction rate constant , kinetics , physics , quantum mechanics
The substituent effect on azo‐hydrazone tautomerization of 1‐arylazonaphthen‐ols is studied by means of NMR analysis. Among the 13 C chemical shifts, the C(2) of this series compound is the most sensitive to the variation in the nature of substituent on the phenyl ring. Therefore, the variation in the chemical shifts of C(2) is used to probe the substituent effect by using the substituent chemical shifts and free energy vs. Hammett’s constant (χρ + ). Both methods give a negative correlation slope, indicating the electron‐with‐ drawing groups favor the hydrazone tautomer form. The effect on the chemical shifts of C(2) of compound 8 in ten solvents can be classified as the solvent with a proton‐donor, proton‐acceptor and arenes system. The substituent with electron‐donating character is more sensitive to the nature of solvent and it favors the hydrazone form. Free energy obtained from the dynamic NMR technique indicates the tautomerization favors the hydrazone‐form for the substituent with electron‐withdrawing character.