Barriers to rotation adjacent to double bonds. 2. n-propyl vs. isopropyl groups

Journal Article · Wed Sep 17 00:00:00 EDT 1986 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00279a025· OSTI ID:5279282

Wiberg, K B

The barriers to rotation about the C-C bonds adjacent to the carbonyl groups of isobutyraldehyde, methyl isopropyl ketone, and isobutyric acid were calculated. The 3-21 G basis set was used for the geometry optimizations, and the 6-31 G basis set was used to obtain the energies. The differences in energy between R = n-propyl and isopropyl also were calculated and reproduced the observed energy differences. Whereas the more branched isomer had a significantly lower energy for the aldehydes and acids, the difference in energy was very small with the ketones. The components of the barrier are discussed. The traditional decomposition into 1-, 2-, and 3-fold terms does not provide a useful representation of the interactions which are involved. Besides the 3-fold barrier observed with compounds having R = CH/sub 3/, the major contributions to the barrier arise from the stabilizing interaction between an alkyl group and the carbonyl (approx. 1 kcal/mol) and from the repulsive interaction between one of the methyls of the isopropyl group and the other substituent at the carbonyl. A hydroxy group (i.e., in a carboxylic acid) leads to a significantly smaller steric interactions than found with a methyl group (i.e., in a methyl alkyl ketone).

• Research Organization: Yale Univ., New Haven, CT
• OSTI ID: 5279282
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 108:19; 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)
ALDEHYDES
CARBONYLS
CARBOXYLIC ACIDS
CHEMICAL BONDS
CONFIGURATION INTERACTION
DATA
DOUBLE BONDS
INFORMATION
ISOBUTYRIC ACID
KETONES
MONOCARBOXYLIC ACIDS
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
PHYSICAL PROPERTIES
STEREOCHEMISTRY
THEORETICAL DATA
THERMODYNAMIC PROPERTIES
THERMODYNAMICS