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Conformational Study of trans-Cyclododecene by Dynamic NMR Spectroscopy and Computational Methods
Diwakar M. Pawar1, Kristie L. Davis, Bennie L. Brown
1Department of Chemistry, Jackson State University, Jackson, Mississippi 39217-0510.
The Journal of Organic Chemistry
|October 25, 2001
Summary
This study reveals trans-cyclododecene (1) exists in multiple conformations in propane at low temperatures. Computational methods predict and NMR data confirm the populations of these distinct C(1) and C(2) symmetric structures.
Area of Science:
- Organic Chemistry
- Physical Chemistry
- Computational Chemistry
Background:
- Trans-cyclododecene (1) is a cyclic olefin whose conformational behavior is of interest.
- Understanding the conformational landscape of such molecules is crucial for predicting their properties and reactivity.
Purpose of the Study:
- To investigate the low-temperature conformations of trans-cyclododecene (1) in solution.
- To compare experimental NMR data with computational predictions for conformational analysis.
Main Methods:
- Low-temperature Nuclear Magnetic Resonance (NMR) spectroscopy ((13)C) was used to study trans-cyclododecene (1) in propane.
- Molecular mechanics (MM2 and MM3) were employed for conformational searching and energy calculations.
- Giao (Gauge-Independent Atomic Orbital) method at the HF/6-311G level was used for calculating (13)C chemical shifts.
Main Results:
- Seven distinct peaks were observed in the (13)C NMR spectrum, indicating multiple conformations.
- Three C(1) symmetric conformations and one C(2) symmetric conformation (20.1% population) were identified.
- Experimental populations for C(1) conformations were 57.0%, 18.6%, and 4.3%.
Conclusions:
- The study successfully characterized the conformational ensemble of trans-cyclododecene (1) at low temperatures.
- Computational results align well with experimental NMR data, validating the predictive power of the applied methods.
- Conformational comparison with cyclododecane (2) provides insights into the influence of the double bond on ring structure.