Thermochemical studies of carbonyl reactions. 2. Steric effects in acetal and ketal hydrolysis

Journal Article · Wed Jul 29 00:00:00 EDT 1981 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00405a030· OSTI ID:6065288

Wiberg, K A; Squires, R R

A calorimetric determination of the enthalpies of hydrolysis of a series of alkyl-substituted dimethyl acetals is reported. These data are critially compared with the enthalpies of hydrolysis from an analogous set of aliphatic dimethyl ketals derived from 2-alkanones. The acetals exhibit a significantly attenuated range in their enthalpies of hydrolysis relative to that for ketal hydrolysis. The free energies of acetal formation in solution were modeled by measurements of the corresponding free energies of themiacetal formation from the aldehydes in neutral methanol. The observed free-energy differences are satisfactorily correlated with the Taft E/sub s/ steric substituent constant scale, but the corresponding acetal enthalpy data vary in a complex manner. The role of entropy in determining kinetic and equilibrium steric effects in a variety of other systems is discussed. Preliminary molecular mechanics calculations on these systems indicate the importance of bond angle bending in evaluating the torsional potential at a carbonyl group. Many of the compounds were found to possess several conformations having comparable energies.

• Research Organization: Yale Univ., New Haven, CT
• OSTI ID: 6065288
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 103:15; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ACETALS
CHEMICAL REACTIONS
DATA
DECOMPOSITION
ENERGY
ENTHALPY
ENTROPY
ETHERS
EXPERIMENTAL DATA
FORMATION FREE ENERGY
FREE ENERGY
HYDROLYSIS
INFORMATION
LYSIS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
REACTION HEAT
SOLVOLYSIS
STEREOCHEMISTRY
THERMODYNAMIC PROPERTIES