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Conformational effects on optical rotation. 3-substituted 1-butenes
Kenneth B Wiberg1, Patrick H Vaccaro, James R Cheeseman
1Department of Chemistry, Yale University, New Haven, Connecticut 067520-8107, USA. kenneth.wiberg@yale.edu
Journal of the American Chemical Society
|February 13, 2003
Summary
The study reveals that molecular conformation significantly impacts optical rotation in (R)-(-)-3-chloro-1-butene, with calculated values differing greatly between torsional angles. Observed rotations were smaller than predicted, suggesting complex factors influence this phenomenon.
Area of Science:
- * Organic Chemistry
- * Computational Chemistry
- * Stereochemistry
Background:
- * Chirality and optical activity are crucial in stereochemistry.
- * Understanding conformational effects on optical rotation is key for predicting molecular properties.
- * (R)-(-)-3-chloro-1-butene serves as a model compound for studying these relationships.
Purpose of the Study:
- * To calculate and analyze the optical rotation of (R)-(-)-3-chloro-1-butene.
- * To investigate the influence of the C=C-C-C torsional angle on optical rotation.
- * To compare theoretical calculations with experimental observations and explore substituent effects.
Main Methods:
- * Theoretical calculation of optical rotation.
- * Conformational analysis based on torsional angles.
- * Temperature-dependent studies to analyze conformational equilibria.
- * Theoretical examination of substituent effects (F, CN, CCH) on optical rotation.
Main Results:
- * A significant dependence of optical rotation on the C=C-C-C torsional angle was calculated.
- * Free energy difference between conformers was determined as 1315 cal/mol.
- * Observed rotations were approximately 2.6 times smaller than calculated values.
- * Substituent effects on optical rotation were found to be minimal.
Conclusions:
- * Molecular conformation plays a critical role in determining optical rotation.
- * Discrepancies between calculated and observed rotations highlight the need for refined theoretical models.
- * The electronic effects of substituents on optical rotation are less pronounced than conformational effects.
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