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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Chair Conformation of Cyclohexane Caption: Torsional energy of butane. Alcanos ramificados tienen p. Torsional strain in cyclopropane. Alkyl substituents on cyclohexane rings will tend to be equatorial to avoid 1,3-diaxial interactions.

conformaciones de butano

The other eclipsed conformations are lower in energy than the totally eclipsed conformation but are still more unstable than the staggered conformations. The only intermolecular force of nonpolar molecules are London dispersion forces which result from induced confotmaciones attractions.

Melting Points of Alkanes Caption: The melting point curve for n-alkanes with even numbers of carbon atoms is slightly higher than that for alkanes with odd numbers of carbons. The axial substituent interferes with the axial hydrogens on C3 and C5.


The eclipsed conformations are higher in energy than the staggered conformations of butane, especially the totally eclipsed conformation. Interconversion between chair conformations require that cyclohexane go through its higher alanos conformations.

Cyclohexane can adopt four non-planar conformations: The simplest alkane is methane, CH4. When there are two carbon chains of the same length, the one that has the most substituents must be chosen to name the compound.


This puckered conformation reduces the eclipsing of adjacent CH2 groups. 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 ring strain of a planar cyclobutane results from two factors: In this case both chairs have the same energy, and they are present in equal amounts.

The conformation of cyclobutane is slightly folded.

When a bond alcanis propane rotates, the torsional energy varies much like it does in ethane, but with 0. The more stable conformation has both methyl groups in equatorial positions.

The angle strain and the torsional strain in cyclopropane make this ring size extremely reactive. Alcanos con par de C tienen p. Butano tiene 2 conformaciones alternadas diferentes: The axial bonds are directed vertically, parallel to the axis of the ring.

Conformational Analysis of Ethane Caption: All the C-H bonds are staggered in the chair conformation. The bond angles are To convert between these two conformations, the molecule must pass through the unstable half-chair conformation.

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.

The following figure shows the severe steric interactions in a chair conformation with a t-butyl group axial. The unfavorable conformation has both methyl groups in axial positions, with a 1,3-diaxial interaction between them.

Some groups are so bulky that they are extremely hindered in axial positions.

There are two possible geometric isomers for decalin: This conformation is lower in energy lo favored over the conformation with the methyl in the axial conformacionnes. Conformations of Ethane Caption: Rotations about the center bond in butane give different molecular shapes.


Axial hydrogens are pointed straight up or down, parallel to the axis of the ring. Alkanes with an even number of carbons pack better than those with an odd number of carbons. As they are numbered here, the odd-numbered carbons have their upward bonds axial and their downward bonds equatorial. Looking down the C1-C2 bond of the equatorial conformation, we find that the methyl group is anti to C3. Newman Projection of Methylcyclohexane: Chair interconversion would still produce an axial and an equatorial methyl.

The different arrangement formed by rotations about a single bond are called conformations, alcannos a specific is called conformer.

Estructura y Estereoquímica de Alcanos – ppt video online descargar

The angle compression for butane is Cyclobutane adopts the folded conformation to decrease the torsional strain caused by eclipsing hydrogens. Alcohols are compounds whose molecules have a hydroxyl.

Methane is perfectly tetrahedral, with the Same Length Chains Caption: In solids, the packing of the molecules into a three dimensional structure affects the melting point. Nomenclature of Alkyl Groups Caption: The eclipsed conformation is about 3. Chair Conformations of cis-1,3-Dimethylcyclohexane Caption: Chair-chair interconversion of methylcyclohexane.

Two chair conformations are possible for cis-1,3-dimethylcyclohexane.