| Summary: | 博士 === 國立臺灣大學 === 化學系 === 86 === A linear relationship δ=24.6σ++556.3 could be useful in estimating the
σ+value for furan and thiophen . The substituent constants σ+value for those-
five membered heteroaromatic ring were determined from 17O NMR substituent
chemical shifts of the carbonyl group in trifluroacetyl derivatives .
The σ+values were found to be -1.08 for 2-furyl , -0.29for 3-furyl , -1.02
for 2-thienyl and -0.52 for 3-thienyl, respectively .
Nucleophilic solvent participation was found in the solvolysis of primary
and secondary-α-methylbenzyl halide , whereas , the solvolysis mechanism for
secondary- α-tert-butylbenzyl derivatives was a limiting SN1 process .
Variation of ρvalue was found in the solvolysis of secondary-α-tert-
butylbenzyl derivatives with the number of data points from electron donor to
electron withdrawing substituent on the benzene ring . It suggested the
possibility of acceleration of the deactivate substrate due to the increasing
significance of solvation to the leaving group .
The σ+value for 2-furyl and 3-furyl , and 2-thienyl and 3-thienyl group
were found to be -1.05,-0.596,-0.931 and -0.545 , respectively , from
extrapolation or interpolation of solvolysis rate data in Hammett-Brown
relationship logk=σ+ρ . Significant difference between this and previous
study by 17O chemical shift for 3-furyl group was noteed.
α-Tert-butylpyridinylmethyl derivatives and some five-membered two-
heteroatom analogous were prepared and were solvolyzed . Poor linear
correlation between logk and YX or YBnX by using Grunwald -Winstein equation.
The range of σ+value of 3-pyridinyl and 2-thiazoyl were 0.450~0.631 and
-0.066~0.008 , respectively , from interpolation of solvolysis rate data in
Hammett-Brown relationship logk=σ+ρ.
Solvolysis of α-tert-butyl(1-naphthyl)methyl and α-tert-butyl(2-
naphthyl)methyl bromides were studied . The σ+values were found to be -0.237
and - 0.189 , respectively .
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