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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conformaciones de butano
Esta interferencia es llamada interacciones 1,3-diaxial. Torsional energy of butane. Newman Projections of Butane Caption: The unfavorable conformation has both methyl groups in axial positions, with a 1,3-diaxial interaction between them. In solids, the packing of the molecules into a three dimensional structure affects the melting point.
Khan Academy on a Stick : conformaciones de butano
Chair interconversion would still produce an axial and an equatorial methyl. In the Newman projection pos is easier to see the steric interaction between the methyl substituent and the hydrogens and carbons of the ring. Propane is shown here as a perspective drawing and as a Newman projection looking down one of the carbon-carbon bonds. Chair Conformations of trans-1,3-Dimethylcyclohexane Caption: The more stable conformation has both methyl groups in equatorial positions.
The only intermolecular force of nonpolar molecules are London dispersion forces which result from induced dipole attractions. Rotations about the center bond in butane give different molecular shapes.
Methane is perfectly tetrahedral, with the The conformation of cyclopentane is slightly folded, like the shape of an envelope. The eclipsed conformations are higher in energy than the staggered conformations of butane, especially the totally eclipsed conformation. The melting point curve for n-alkanes with even numbers of carbon atoms is slightly higher than that conformacionees alkanes with odd numbers of carbons.
Boat Conformation of Cyclohexane Caption: This conformation is lower in conforrmaciones and favored over the conformation with the methyl in the axial position. Two chair conformations are possible for cis-1,3-dimethylcyclohexane.
Estructura y Estereoquímica de Alcanos
All the C-H bonds are staggered in the chair conformation. The different arrangement formed by rotations about a single bond are called conformations, and a specific is called conformer. The anti conformation is lowest in conformwciones, and the totally eclipsed conformation is highest in energy.
To convert between these two conformations, the molecule must pass through the unstable half-chair conformation.
Conformational Analysis of Ethane Caption: The angle strain and the torsional strain in cyclopropane make this ring size extremely reactive. Comparison of the boiling points of the unbranched alkanes blue with those of some branched alkanes red. The following figure shows the severe steric interactions in a alcanox conformation with a t-butyl group axial. Cyclic compound with 4 carbons or more adopt non-planar conformations to relieve ring strain.
This interference is called a 1,3-diaxial interaction. Often, the longest chain with the most substituents is not obvious. Melting Points of Alkanes Caption: The axial bonds are directed vertically, parallel to the axis of the ring.
Newman Projection of Methylcyclohexane: Totally Eclipsed Conformation of Butane Caption: Regardless of the other groups present, the most stable conformation has a t-butyl group in an equatorial position.
The equatorial bonds are directed outward, toward the equator of the ring. 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 ring strain of a planar cyclobutane results from two factors: Angle Strain in Cyclopropane Caption: The simplest alkane is methane, CH4. Cyclohexanes with tertiary-butyl substituents show that an axial t-butyl group is severely hindered.
The chair conformation is most stable, followed by the twist boat. Torsional energy of propane. The C-C bond distance is 1. The torsional energy of ethane is lowest in the staggered conformation. In this case both chairs have the same energy, and they are present in equal amounts. Ambas conformaciones tienen un metil axial y otro ecuatorial. Structures of some cycloalkanes. The Newman projection looks straight down the carbon-carbon bond. Nomenclature of Alkyl Groups Caption: Longer chained alkanes have greater surface area and can have more surface contact and more induced dipoles than branched alkanes with smaller surface areas.