Os alcanos son hidrocarburos, é dicir que teñen só átomos de carbono e .. difiren en enerxía: a conformación alternada é 12,6 kJ/mol menor en enerxía (por . Presentación del tema: “Estructura y Estereoquímica de Alcanos”— . Conformaciones son diferentes arreglos de los átomos producidos al rotar el enlace σ. Análisis conformacional del etano Análisis conformacional del butano Mecánica molecular aplicada a los alcanos y los cicloalcanos

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Since the methyl group occupies more space than a hydrogen, the torsional strain will be 0. The staggered conformations are lower in energy than the eclipsed conformation because the staggering allows the electron clouds of the C-H bonds to be as far apart as possible.

Torsional energy of butane. When there are two carbon chains of the same length, the one that has the most substituents must be chosen to name the compound. Conformations of Cyclohexane Caption: In the actual molecule, the boat conformation is skewed to give the twist boat, a conformation with less eclipsing of bonds and less interference between the two flagpole hydrogens.

The axial substituent interferes with the axial hydrogens on C3 and C5. All the C-H bonds are staggered lod the chair conformation. When a bond of propane rotates, the torsional energy varies much like it does in conformacilnes, but with 0.



For butane there will be two different staggered conformations: The angle compression of cyclopropane is The following figure shows the severe steric interactions in a chair conformation with a t-butyl group axial.

In the symmetrical boat conformation of cyclohexane, eclipsing of bonds results in torsional strain. The methyl group is axial in one conformation, and equatorial in the other.

Torsional strain in cyclopropane. This puckered confrmaciones reduces the eclipsing of adjacent CH2 groups. Alcanos ramificados tienen p. The equatorial bonds are directed outward, toward the equator of the ring. The Newman projection looks straight down the carbon-carbon bond.

Conformations of Ethane Caption: The anti conformation is lowest in energy, and the totally eclipsed conformation is highest in energy. Numbering from left to right gives the first branch on C2; numbering from right to left gives the first branch on C3, so we number from left to right.

The eclipsed conformations are higher in energy than the staggered conformations of butane, especially the totally eclipsed conformation. Angle Strain in Cyclopropane Caption: When looking for the longest continuous chain, look to find all the different chains of that length.

When molecules can pack in neat order avoiding empty pockets the melting point will be higher than when the packing is not ordered. Propane is shown here as a perspective drawing and as a Newman projection looking down one of the carbon-carbon bonds. The conformation of cyclobutane is slightly folded. The six-membered rings in cis- and trans-decalin assume chair conformations.


The other eclipsed conformations are lower in energy than the totally eclipsed conformation but are still more unstable than the staggered conformations.

Estructura y Estereoquímica de Alcanos

To convert between these two conformations, the molecule must pass through the unstable half-chair conformation. The torsional energy of ethane is lowest in the staggered conformation. An equatorial methyl group will be anti to the C3. Alkanes with an even conformacioens of carbons pack better than those with an odd number of carbons.

Torsional energy of propane. Melting Points of Alkanes Caption: Much like ethane the staggered conformations of propane is lower in energy than the eclipsed conformations.

Rotations about the center bond in butane give different molecular shapes. Totally Eclipsed Conformation of Butane Caption: All the carbon-carbon bonds are eclipsed, generating torsional strain that contributes to the total ring strain. Esta interferencia es llamada interacciones 1,3-diaxial.