Decide which conformation of ethane is the most stable. Click on a hydrogen, then the carbon bonded to it, then the next carbon and then a hydrogen bonded to the second carbon. Ethane is structurally the simplest hydrocarbon that contains a single carboncarbon bond. These are the lowest energy structure, called the staggered conformation, and the highest energy structure, called the eclipsed conformation. The differences in these two conformations for ethane can easily be seen by viewing them both on the screen simultaneously. Conformations are different arrangements of atoms that result from bond rotation. Conformational analysis of cycloalkanes pdf paperity. It occurs when the atoms are in eclipsed conformation. Click on the 6c button in the upper left of the toolbar. Conformation free download as powerpoint presentation. Conformational behavior of ethane molecule encapsulated in a nanotube article pdf available in russian journal of organic chemistry 498.
Jun 09, 2010 illustration and interconversion of staggered and eclipsed ethane conformatiobs with space ffilling and ball stick models. Ethane in the staggered conformation has 2 c3 axes the cc line, 3 perpendicular c2. The 1,2disubstituted derivatives of ethane were for a long time topic of the conformational studies carried out by experimental as well as theoretical methods. This wedge and dash drawing represents one conformation of ethane. The theory is introduced with reference to trying to explain why the eclipsed form of ethane is 2. Energy of eclipsed and staggered conformations of ethane and. These isomers are termed as conformational isomers. Although an infinite number of conformations are possible, the staggered and eclipsed conformations which represent the most and least stable respectively are the two most important. Why does the gauche conformation of ethane1,2diol show. Why does the gauche conformation of ethane 1,2diol show hydrogen bonding even though there is no 6membered ring system. If we rotate this a little bit, well see the staggered conformation of ethane from a sawhorse perspective. Pdf the interplay of solvation, molecular conformation. Dec 29, 2014 lets start with a wedgedash view of the staggered conformation of ethane.
The second most important constituent of natural gas. We know that theres free rotation around this carboncarbon single bond. One position where c 1 and c 4 are in opposite positions is known as the trans conformation, the other where they are adjacent is known as the gauche conformation. Rotation of the bond in the anti conformation 60 o leads to an eclipsed conformation. Organic chemistry computational modeling experiment. Barton britain and both were awarded nobel prize in 1969. Part of the crystal structure of i, showing the formation of a hydrogenbonded chain of r 2 2 8 rings running parallel to the 101 direction. Conformation of ethane butane and cyclohexane edubuzz notes. For each of the 100 ligands under study, we obtained a local minimum conformation with an mwrmsd of ethane molecule in the eclipsed conformation is said to suffer from torsional strain and by a rotation around the carbon carbon bond to the staggered conformation around 12. What is the staggered conformation of ethane using the. May 25, 2019 conformations of ethane ethane is an organic chemical compound. To do the same process, you may simply click the left mouse button on the following icon.
Conformations of ethane organic chemistry khan academy. Organic chemistry university of california riverside. Construct an explanation of why conformer a is called staggered and conformer b is called eclipsed. The ethane molecule, c2h6, can exist in both the staggered and eclipsed conformations where the staggered conformation is slightly more stable. The conformation in which the newman projection shows all six hydrogens of ethane in plain view is a staggered conformation.
It has no torsional strain as all the ch bonds are staggered to each other. The least stable high energy conformation is the one in which the six carbon hydrogen bonds are as close as possible eclipsed in a newman projection. The adiabatic and vertical energy differences eclipseda staggered. Weve just seen that the staggered conformation of ethane is more stable than the eclipsed conformation of ethane.
In the staggered conformation, all of the ch bonds on the front carbon are positioned at an angle of 60 relative to the ch bonds on the back carbon. In step 8c, choose two h atoms that eclipse each other. This type of rendering is called a newman projection. Torsional strain repulsion between bonds ethane 12 kjmole chch bond interaction 4 kjmole. At room temperature, theres enough energy for the staggered conformation to turn into the eclipsed. Further rotation gives the least stable conformation in which the hydrogens are. A view of ethane seen by looking along the cc bond axis. Rotation about the cc bond in ethane see the jsmol animation to the right produces different conformations.
Theoretical study of structure of the 1,2disubstituted derivatives of. Hatch sawhorse newman projection although they are oriented differently and use different methods of drawing, each of the six representations above shows ethane ch3ch3 in its lowest energy most favorable conformation. The energy barrier must be small for conformational isomerism to occur. Since they are different compounds, they should lie on different energy diagrams. The least stable high energy conformation is the one in which the six carbonhydrogen bonds are as close as possible eclipsed in a newman projection. Conformations and configurations never mistake them. The chair conformation is the most stable conformation of cyclohexane because all of the bond angles around the carbon atoms are at 109. Ethane, a colourless, odourless, gaseous hydrocarbon compound of hydrogen and carbon, belonging to the paraffin series. Conformations of organic molecules columbia university. Energetics of rotation about sigma bonds staggered and eclipsed conformations a. Conformations of ethane and butane conformational isomerism.
All staggered and eclipsed conformations of 1,2ethanediol, 2amino ethanol, and 1,2ethanediamine have been studied by the semiempirical. The lowest energy conformation of ethane, shown in the figure above, is called the staggered conformation. If they are not interconvertible, they are called con. Conformation means the different arrangement of atoms in space that result from rotations of groups about a single bond. Conformations of ethane experiments show that there is a 12 kjmol 2. Imagine picking up the ethane molecule with your left hand, grasping it at the center of the ccbond, holding it up to your eye, and looking down the ccaxis. Preference of small molecules for local minimum conformations. Forcing the staggered conformation of ethane select file new from the main menu or click on the toolbar and build ethane as described above. Here we have the staggered conformation of ethane, looking at it from a wedge and dash perspective. At standard temperature and pressure, ethane is a colorless, odorless gas. Conformations of ethane ws10 questions key chem 211 dr. We are now going to create the eclipsed conformation of ethane.
Eclipsed ethane has 12 kj per mol more energy than the staggered conformation. Conformations of organic molecules what do the terms staggered and eclipsed mean. Since rotation around the cc bond of ethane is continuous, there are an infinite number of conformations, but only two are of major interest. If you want turn a staggered conformation into an eclipsed conformation, you would need energy.
A sawhorse projection is a view of a molecule down a particular carboncarbon bond groups connected to both the front and back carbons are drawn using sticks at 120 angles. Conformational analysis i newman projections model 1. Newman projections a method of depicting organic molecules 2. When finished, return to the job manager by clicking either blue arrow. It will be readily apparent from the butane model that interference occurs between the hydrogen atoms on c1 and c 4 carbon atoms in the gauche conformation. How to represent the staggered and eclipsed conformations of ethane. If two different 3d arrangements in space of the atoms in a molecule are interconvertible merely by free rotation about bonds, they are called conformations. Start by closing the file for your staggered conformation of ethane by clicking file in the upper left corner of the screen and then click close. Follow the directions listed above to constrain the cccc dihedral angle. The most stable low energy conformation is the one in which all six ch bonds are as far away from each other as possible staggered when viewed endon in a newman projection. Molecular modeling and conformational analysis with pc spartan. Conformational analysis of ethane video khan academy. Pdf conformational behavior of ethane molecule encapsulated.
Conformational analysis structures that can be interconverted by rotation about single bonds are conformations of the same molecule. The chair conformation can be viewed as having two carbon atoms on the plane of the paper. Continued rotation leads to a staggered conformation in which the methyl groups are close to each other, called the gauche conformation. Two in another plane in front of the paper and the remaining two in a. So lets watch the video and look at the different conformations of ethane. Conformational analysis college of saint benedict and saint. This file contains additional information such as exif metadata which may have been added by the digital camera, scanner, or software program used to create or digitize it.
Rotational energy acts as a barrier in case of single bond rotation. The lowest energy conformation of ethane, shown in the figure above, is called the staggered conformation, in which all of the ch bonds on the front carbon are positioned at dihedral angles of 60relative to the ch bonds on the back carbon. Cyclohexane is the only cyclic structure that allows all the bond angles around each carbon to be 109. From the given diagram, either r or s could represent eclipsed confirmation of ethane and p or q could represent staggered confirmation of propane. Pdf the interplay of solvation, molecular conformation and.
The ethane molecule in the eclipsed conformation is said to suffer from torsional strain and by a rotation around the carbon carbon bond to the staggered conformation around 12. In this conformation, the distance between the bonds and the electrons in them is maximized. The two red hydrogens, called flagpole hydrogens, approach each other too closely and cause some steric strain. The illustration of butane above is represented by the newman. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petrochemical byproduct of petroleum refining. Poutsma 1 worksheet 10 answer key conformations of ethane what is the overall 3d structure of ethane. Chapter 2 chain conformation in polymers polymerization various long chains molecules of polymers collection of these long chains states and properties of polymers plastics, rubbers or fibers polymer chains can be flexible or rigid stiff, non flexible and polymers could be crystalline or amorphous. Select the builder fragment by clicking on the button on the bottom middle of the toolbar it might say carbon tetrahedral or something similar. Conformations representing energy minima are termed conformers. It is a colorless and odor gas at a standard temperature. Select measure dihedral from the geometry menu or click on. Energy diagram for rotation about the cc bond in ethane. In the case of the staggered conformation, the input file would be the following. Pdf the energy change on each occupied molecular orbital as a function.
457 345 1606 1685 535 209 81 199 679 585 1223 627 1244 118 1488 1216 157 882 1318 345 1278 1115 1007 1314 43 1202 263 811