Correlation tetrahydropyranyl acetals

Fig. 5.18. Correlation between change in ground-state structure (q(, = (Ar Q + Ar o) ) and activation energy for spontaneous cleavage of tetrahydropyranyl acetals (dotted line). Reaction profiles for the slowest and fastest reaction are also shown...

Fig. 6.46. Correlation between change in ground-state structure q) and activation energy (D) in tetrahydropyranyl acetals (Scheme 6.32). experimental values, dotted line calculated from Equation 6.13 solid lines energy profiles for slowest and fastest reactions...

The relationship, between magnitudes of these sensitivity parameters and the reactivity of the system concerned, was explored quantitatively for three sets of acetal structures, and a further linear relationship was found (Kirby and Jones, 1986). Figure 25 shows a plot of the sensitivity parameter against relative reactivity for series of compounds, tetrahydropyranyl-, methoxymethyl- and a-glucosyl-OX, known to react with C-OX cleavage at very different rates (relative rates of hydrolysis approximately 1, 103 5 and 106 5, respectively). The correlation is good for both the intercepts (i.e. the... 

In view of the described effects of substitution on heterolytic bond cleavage rate and on the scissile bond length, it is not surprising that this bond distance is correlated with reactivity and that the correlation holds for variation at both ends of the bond. Indeed, Jones and Kirby point out that there are excellent linear correlations of log with intercepts and slopes of the corresponding bond length-pAfa plots for the series a-glucosides, methoxymethyl acetals, and axial tetrahydropyranyl... 

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