Conformational Analysis of 1,3-Difluorinated Alkanes
William G Poole1, Florent Peron1, Stephen J Fox1
1School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, U.K.
The Journal of Organic Chemistry
|May 31, 2024
Summary
Fluorine substitution significantly impacts molecular shape, especially with the 1,3-difluoropropylene motif in alkanes. This effect intensifies with longer chains and varies with solvent polarity.
Area of Science:
- Organic Chemistry
- Computational Chemistry
- Spectroscopy
Background:
- Fluorine substitution is a key strategy to modulate molecular conformation and properties.
- Understanding the conformational behavior of fluorinated alkanes is crucial for designing new molecules.
Purpose of the Study:
- To analyze the conformational impact of the 1,3-difluoropropylene motif in various alkane chains.
- To investigate the influence of medium polarity and chain length on these conformational effects.
- To demonstrate advanced NMR simulation techniques for complex spin systems.
Main Methods:
- Detailed conformational analysis of 1,3-difluoropropane, 2,4-difluoropentanes, and 3,5-difluoroheptanes.
- Nuclear Magnetic Resonance (NMR) spectroscopy for experimental data acquisition.
- Polynomial complexity scaling simulation algorithms for J-coupling extraction from complex spectra.
Main Results:
- The 1,3-difluoropropylene motif strongly dictates alkane chain conformation.
- Conformational effects are dependent on solvent polarity and are magnified in longer chains.
- Advanced NMR simulations successfully analyzed large, strongly coupled spin systems.
Conclusions:
- The 1,3-difluoropropylene motif offers a powerful tool for controlling aliphatic chain conformation.
- Simple rules for conformation population analysis were derived.
- Quantum mechanical time-domain NMR simulations are effective for complex liquid-state systems.
Related Concept Videos
02:29Conformations of Cycloalkanes
11.8K
Adolf von Baeyer attempted to explain the instabilities of small and large cycloalkane rings using the concept of angle strain — the strain caused by the deviation of bond angles from the ideal 109.5° tetrahedral value for sp3 hybridized carbons. However, while cyclopropane and cyclobutane are strained, as expected from their highly compressed bond angles, cyclopentane is more strained than predicted, and cyclohexane is virtually strain-free. Hence, Baeyer’s theory that...
11.8K
02:18Conformations of Ethane and Propane
13.9K
In an organic molecule, free rotation about the carbon-carbon single bond results in energetically different conformers of the molecule. Due to this rotation, called the internal rotation, ethane has two major conformations — staggered and eclipsed.
Staggered conformation is a low energy and more stable conformation with the C-H bonds on the front carbon placed at 60°dihedral angles relative to the C-H bonds on the back carbon, leading to a reduced torsional strain. In staggered...
Staggered conformation is a low energy and more stable conformation with the C-H bonds on the front carbon placed at 60°dihedral angles relative to the C-H bonds on the back carbon, leading to a reduced torsional strain. In staggered...
13.9K
02:20Conformations of Butane
14.1K
Unlike ethane and propane that have only two major conformations, butane has more than two conformers. The staggered form of butane in which the bulky methyl groups on the two carbons are placed on opposite sides, that is, at a dihedral angle of 180°, is the lowest energy, most stable form — called the anti conformer. This conformation is stabilized due to the absence of steric repulsion between the largely spaced out methyl groups. The other two staggered conformations are...
14.1K
02:18Constitutional Isomers of Alkanes
18.0K
Organic compounds of the same molecular formula can have different structural formulas called constitutional isomers, and the phenomenon is known as constitutional isomerism. Alkanes with four or more carbons showing multiple structures with the same molecular formula thereby exhibit constitutional isomerism.
The linear isomer of an alkane is prefixed by the term “n”; hence a linear isomer of pentane is known as n-pentane. Based on the type of branching, some of the...
The linear isomer of an alkane is prefixed by the term “n”; hence a linear isomer of pentane is known as n-pentane. Based on the type of branching, some of the...
18.0K
02:02Chair Conformation of Cyclohexane
14.6K
The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this...
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this...
14.6K
02:33Physical Properties of Alkanes
10.9K
Alkanes are nonpolar molecules due to the presence of only carbon and hydrogen atoms. The electronegativity difference between carbon and hydrogen is minimal, and hence alkanes have a zero dipole moment. This leads to the presence of only dispersion forces between the molecules. The strength of dispersion forces is dependent on the surface area of the molecules on which they act. Since the surface area increases with the molecular length for straight-chain alkanes, the dispersion forces also...
10.9K