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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Los botones se encuentran debajo. C5H12 C H 3 2 n-pentano iso-pentano conformacions Chapter 3. Same Length Chains Caption: When looking for the longest continuous chain, look to find all the different chains of that length. Often, the longest chain with the most substituents is not obvious. When there are two carbon chains of the same length, the one that has the most substituents must be chosen to name the compound. Nomenclature of Alkyl Groups Caption: Some common alkyl groups and their names.
Substituents on a carbon chain are called alkyl groups. They are named by replacing the -ane ending of the alkane with -yl. Solution The longest carbon chain contains eight carbon atoms, so this compound is named as an octane. Numbering from left to right gives the first branch on C2; numbering from right to left gives the first branch on C3, dee we number from left to right. Comparison of loss boiling points of the unbranched alkanes blue with those of some branched alkanes red.
Because of their smaller surface areas, branched alkanes have lower boiling points than unbranched alkanes. Alcaos only intermolecular force of nonpolar molecules are London dispersion forces which result from induced dipole attractions.
Longer chained alkanes have greater surface area and can have more surface contact and more induced dipoles than branched alkanes with smaller surface ve. Alcanos con par de C tienen p. Alcanos ramificados tienen p.
Estructura y Estereoquímica de Alcanos
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.
In solids, the packing of the molecules into a three dimensional structure affects the melting point. When molecules can pack in neat order avoiding empty pockets the melting point will be higher than when the packing is not ordered. Alkanes with an even number of carbons pack better than those with an odd number of carbons.
The simplest alkane is methane, CH4. Methane is perfectly tetrahedral, with the The four hydrogen atoms are covalently bonded to the central carbon atom, with bond lengths of 1. Any carbon with four sigma bonds has an sp3 hybridization. Ethane, the two-carbon alkane, is composed of two methyl groups with overlapping sp3 hybrid orbitals forming a sigma bond between them.
Ethane cohformaciones two sp3 carbons. Alccanos C-C bond distance is 1. Conformations of Ethane Caption: The different arrangement formed by rotations about a single bond are called conformations, and a specific is called conformer. Pure conformers cannot be isolated in most cases, because the molecules are constantly rotating through all the possible conformations.
Khan Academy on a Stick : conformaciones de butano
Some conformations can be more stable than others. The Newman projection looks straight down the carbon-carbon bond. The Newman projection is the best way to judge the stability of the different conformations of a molecule. Conformational Analysis of Ethane Caption: The torsional energy of ethane is lowest in the staggered conformation. The eclipsed conformation is about 3. At room temperature, this barrier is easily overcome, and the molecules rotate constantly.
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.
La eclipsada es 3.
The Newman Projection of Propane Caption: Propane is shown here as a perspective drawing and as a Newman projection looking down one of the carbon-carbon bonds.
Conformational Analysis of Propane Caption: Torsional energy of propane. When a bond of propane rotates, the torsional energy varies much like it does in ethane, but with 0. Much like ethane the staggered conformations of propane is lower in energy than the eclipsed conformations. Since the methyl group occupies more space than a hydrogen, the torsional strain will be 0. Newman Projections of Butane Caption: Rotations about the center bond in butane give different molecular shapes.
Three of these conformations are given specific names. For butane there will be two different staggered conformations: Confotmaciones tiene 2 conformaciones alternadas diferentes: Conformational Analysis of Butane Caption: Torsional energy of butane.
The anti conformation is lowest in energy, and the totally eclipsed conformation is highest in energy. The eclipsed conformations are cinformaciones in energy than the staggered conformations of butane, especially the totally eclipsed conformation. Among the staggered conformations, the anti is lower in energy because it has the electron clouds of the methyl groups as far apart as possible.
Totally Eclipsed Conformation of Butane Caption: The totally eclipsed conformation is about 1. This kind of interference between two bulky groups is called steric strain or steric hindrance. The other eclipsed conformations are lower in energy than the totally eclipsed conformation but are still more unstable than the staggered conformations.
Structures of some cycloalkanes. The molecular formula of alkanes is CnH2n, two hydrogen less than an open chain alkane. Their physical properties resemble those of alkanes. Angle Strain in Cyclopropane Caption: Angle strain in cyclopropane. The angle compression of cyclopropane is The high reactivity of cyclopropanes is kos to the non-linear overlap of the sp3 orbitals.
Conformations of Cyclopropane Caption: Torsional strain in cyclopropane.
Análisis conformacional by Química Orgánica on Prezi
All the carbon-carbon bonds are eclipsed, generating torsional strain that contributes to the total ring strain. The angle strain and the torsional strain in cyclopropane make this ring size extremely reactive. The ring strain of a planar cyclobutane results from two factors: The angle compression for butane is Angle strain and torsional strain account for the high reactivity of 4-membered rings.
Conformations of Cyclobutane Caption: The conformation of cyclobutane is slightly folded. Folding gives partial relief from the eclipsing of bonds, as shown in the Newman projection. Compare this actual structure with the hypothetical planar structure in Figure oos Cyclic compound with 4 carbons or more adopt non-planar conformations to relieve ring strain. Cyclobutane adopts the folded conformation to decrease the torsional strain caused by eclipsing hydrogens. Conformations of Cyclopentane Caption: The conformation of cyclopentane is slightly folded, like the shape of an envelope.
This puckered conformation reduces the eclipsing of adjacent CH2 groups. To relieve ring strain, cyclopentane adopts the envelope comformaciones. Conformations of Cyclohexane Caption: The chair conformation of cyclohexane has one methylene group puckered upward and another puckered downward. Viewed from the Newman projection, the chair conformation has no eclipsing aclanos the carbon-carbon bonds. The bond angles are Cyclohexane can adopt four non-planar conformations: The most stable conformation is the chair because it has all the C-H bonds staggered.
Boat Conformation of Cyclohexane Caption: In the symmetrical boat conformation of cyclohexane, eclipsing of bonds results in torsional strain. 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.
There is steric hindrance between these hydrogens so the molecule twists a little producing the alcanks boat conformation which is 1.
Conformational Energy Diagram of Cyclohexane Caption: Conformational energy of cyclohexane.