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Does the Anomeric Effect in Ketals Depend on the Hybridization of the Central Carbon Atom?

✍ Scribed by Sergey P. Verevkin; Wei-Hong Peng; Hans-Dieter Beckhaus; Christoph Rüchardt

Publisher
John Wiley and Sons
Year
1998
Tongue
English
Weight
189 KB
Volume
1998
Category
Article
ISSN
1434-193X

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✦ Synopsis

Enthalpies of formation ∆H f °(g) of ketals prepared from ketals have also been determined experimentally and compared with values obtained from molecular mechanics cyclopropanone, cyclobutanone, cyclopentanone, cyclohexanone, and 7-norbornanone with methanol, ethylene calculations (MM3). The close agreement of the results shows that the anomeric interactions, which are already glycol, and 2,2-dimethyl-1,3-propanediol, as well as of acetals/ketals of acyclic aldehydes and ketones, have been integrated in the MM3 force field, are not dissimilar in the small-ring cyclic and spirobicyclic ketals investigated in this determined by measuring their heats of combustion and their heats of sublimation/vaporization. Group increments study. The hybridization of the anomeric carbon atom apparently has no influence on the size of the anomeric effect defining the strain-free energy level have been derived from the collected experimentally determined ∆H f °(g) values of detectable. The strain enthalpies of the cyclic and spirobicyclic ketals have therefore been calculated from their unstrained acetals and ketals, and the anomeric stabilizations of these groups (given in brackets) have been ∆H f °(g) values using the group increment scheme. Analysis and interpretation of all geminal interactions known in calculated from a comparison of their group increments with those of ethers: CH 2 [2O, C] -64.9 (-20.2), CH[2O, C] -63.5 acetals/ketals is possible by means of a recently developed additivity scheme, and a single value of -38.6 kJ mol -1 has (-21.3), C[2O, 2C] -61.9 (-26.8), CH[2O, Ph] -58.4 (-16.2), C[2O, Ph, C] -56.3 (-21.2), C[2O, 2Ph] -67.1 (-32.0) kJ mol -1 .

been obtained for the structural increment representing the inherent geminal O-C-O interactions. Enthalpies of formation ∆H f °(g) of cyclic and spirobicyclic [᭛] For Part 15, see ref. [5] . viewed and were rationalized by a new concept of geminal

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