Download Wade03 estructura y estereoquimica de alcanos . leccin 5. alcanos y cicloalcanos – orgnica 2 leccin 5. Documents. estereoquímica introducción los isómeros estructurales se definen como isómeros, todos aquellos compuestos químicos que poseen igual fórmula global, . Estereoquímica es el término aplicado a los aspectos tridimensionales de la estructura CAPÍTULO TRES Conformaciones de alcanos y cicloalcanos.
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Much like ethane ciloalcanos staggered conformations of propane is lower in energy than the eclipsed conformations. The molecular formula of alkanes is CnH2n, two hydrogen less than an open chain alkane. Chair Conformation of Cyclohexane Caption: Name the groups attached to the chain, using the carbon number as the locator.
Alkyl substituents on etereoquimica rings will tend to be equatorial to avoid 1,3-diaxial interactions. Some conformations can be more stable than others. Los substituyentes axiales interfieren con los H axiales del C 3 y C 5. Solution The longest carbon chain contains eight carbon atoms, so this compound is named as an octane. In this case both chairs have the same energy, and they are present in equal amounts. Boat Conformation of Cyclohexane Caption: Because of their smaller surface areas, branched alkanes have lower boiling points than unbranched alkanes.
Ciclalcanos are two cicloalxanos geometric isomers for decalin: All the carbon-carbon bonds are eclipsed, generating torsional strain that contributes to the total ring strain. The even-numbered carbons have their downward bonds axial and their upward bonds equatorial. For ethane, only 3. Pure conformers cannot be isolated in most cases, because the molecules are constantly rotating through all the possible conformations. The conformation of cyclopentane is slightly folded, like the shape of an envelope.
Newman Projection of Methylcyclohexane: The high reactivity of cyclopropanes is due to the non-linear overlap of the sp3 orbitals. These conformations have equal energies, and they are present in equal amounts.
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When looking for the longest continuous chain, look to find all the different chains of that length. The unfavorable conformation has both methyl groups in axial positions, with a 1,3-diaxial interaction between them.
Newman Projections of Butane Caption: Sobre el proyecto SlidePlayer Condiciones de uso. The melting point curve for n-alkanes with even numbers of carbon atoms is slightly higher than that esteroequimica alkanes with odd numbers of carbons. Either of the chair conformations of trans-1,3-dimethylcyclohexane has one methyl group in an axial position and one in an equatorial position. The six-membered rings in cis- and trans-decalin assume chair conformations.
Wade03 estructura y estereoquimica de alcanos
The ring strain of a planar cyclobutane results from two factors: Conformational Energy Diagram of Cyclohexane Caption: Cyclobutane adopts the folded conformation to decrease the torsional strain caused by eclipsing hydrogens. An equatorial methyl group will be anti to the C3. Ignore di- tri- etc. For butane there will be two different staggered conformations: May be cycloalkyl attachment to chain.
Often, the longest chain with the most substituents is not obvious. The torsional energy of ethane is lowest in the staggered conformation.
This kind dde interference between two bulky groups is called steric strain or steric hindrance. Methane is perfectly tetrahedral, with the Conformations of Cyclobutane Caption: Conformational Analysis of Butane Caption: Ethane, the two-carbon alkane, is composed of two methyl groups with overlapping sp3 hybrid orbitals forming a sigma bond between them.
In the symmetrical boat conformation of cyclohexane, eclipsing of bonds results in torsional strain. 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. Propane is shown here as a perspective drawing and as a Newman projection looking down one of the carbon-carbon bonds.
Estructura y Estereoquímica de Alcanos
In solids, the packing of the molecules into a three dimensional structure affects the melting point. The equatorial bonds are directed outward, toward the equator of the ring. They are named by replacing the -ane ending of the alkane with -yl.
Chair-chair interconversion of methylcyclohexane. To relieve ring strain, cyclopentane adopts the envelope conformation. Bridged rings share two nonadjacent Cs. Conformational Analysis of Propane Caption: No angle strain and no torsional strain. Ambas conformaciones tienen un metil axial y otro ecuatorial.
Alkanes with an even number of carbons pack better than those with an odd number of carbons.