Interactive n→σ* delocalizations that control an aqueous organic equilibrium
Hydrated acetaldehydes were condensed in D2O with substituted alcohols and thiols to determine ΔG of hemiacetalization by 1H NMR. Specific n→σ* delocalizalions in the alkoxy/alkylthio functionality of the product interact to influence n→σ* delocalization in the hemiacetal functionality. Delocalization in the latter functionality controls ΔG.
Fan, Yun-Hua,Haseltine, John
p. 9279 - 9282
(2007/10/03)
Chlorine NQR on Hemiacetals of Chloral, Cl3CCH(OH)OR
The 35Cl NQR spectra of 22 hemiacetals of chloral, Cl3CCH(OH)OR, were studied.Most of these hemiacetals with R = unbranched aliphatic group, show a three line 35Cl NQR spectrum having a regular splitting pattern; two lines around νL = 38.6 +/- 0.1 MHz and the third line at νH = 39.0 +/- 0.1 MHz.It is assumed that the difference between νL and νH is due to "chemical splitting".Completely irregular splitting pattern are found for the hemiacetals carrying bulky branched aliphatic groups.Moreover the magnitudes of these splittings are relatively large.A deformation of the molecules due to intramolecular steric hindrance seems to be responsible for this large splitting.The frequency shift in these compounds due to the steric effect is estimated to be 1 MHz or less.A peculiar temperature dependence of the 35Cl NQR line intensity was found for chloral n-butylhemiacetal.An intramolecular bifurcated hydrogen bond between CCl3 and OH groups is proposed to be responsible for the phenomenon.For p-chlorobenzylalcohol at ca. 226 K a phase transition was observed.
Hashimoto, M.,Weiss, Alarich
p. 134 - 141
(2007/10/02)
Study of the hemiacetals and hemimercaptals of chloral