Organic chemistry computational modeling experiment introduction. We are now going to create the eclipsed conformation of ethane. Differing conformations of a molecule have different. Conformations of organic molecules the organic chemistry of. Chapter 3 conformations of alkanes and cycloalkanes.
The most stable conformation of ethane is the staggered conformation. To do the same process, you may simply click the left mouse button on the following icon. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Alkane and cycloalkane conformations each student work group choose a leader reads activity out loud, poses questions to group, facilitator makes sure everyone is participating equally, directs the conversation, recorder takes notes on discussion, learned concepts and any conclusions, and presenter announces conclusions or presents activity to. Conformations of ethane ethane has two conformations, the staggered conformation and the eclipsed conformations. The illustration of butane above is represented by the newman. Decide which conformation of ethane is the most stable. This wedge and dash drawing represents one conformation of ethane. Equilibrium is reached between the two conformations, and at room temperature, approximately 99% of ethane molecules have an approximately staggered conformation, whereas only about 1% have an eclipsed conformation. Since the eclipsed conformation is higher in energy, there is an energy barrier that must be overcome in rotation around the cc single bond. And this wedge and dash drawing right now represents whats called the staggered conformation of ethane. Eclipse conformation is one of the highest conformation. The chair conformation can be viewed as having two carbon atoms on the plane of the paper. In summery conformational isomers are stereoisomers that can be converted from one isomer to other isomers by rotation about cc bond.
The chair conformation of cyclohexane is the most stable. Theoretical study of structure of the 1,2disubstituted derivatives of. This type of representation makes it easy to assess the torsional angle between two bonds one at each carbon atom. We know that theres free rotation around this carboncarbon single bond. Cyclohexane is the only cyclic structure that allows all the bond angles around each carbon to be 109. The most stable conformation of ethane is the staggered. Conformational analysis of cycloalkanes springerlink. In step 8c, choose two h atoms that eclipse each other. The energy barrier must be small for conformational isomerism to occur. Click on a hydrogen to extend methane to ethane, propane, etc.
Eclipsed and staggered conformation of ethane are drawn and manipulated with chem sketch and its 3d viewer. Staggered conformation eclipsed conformation another view the conformations of propane, butane and all other conformations have the same property as the ethane so they all are conformational isomers. The energy barrier opposing the rotation in ethane is small. Conformational analysis of ethane video khan academy. What links here related changes upload file special pages permanent link. As the hydrogen has a partial positive charge would any of the other carbon bonded hydrogens also. It has a role as a refrigerant and a plant metabolite. The drawing on the left is a flat picture but uses the convention of the bond that is the solid. Minimize with the energy minimizer under the mm2, minimize energy command. At standard temperature and pressure, ethane is a colorless, odorless gas. A can thus be classified as a rotamer a class of conformers. Here we have the staggered conformation of ethane, looking at it from a wedge and dash perspective. While any two arrangements of atoms in a molecule that differ by rotation about single bonds can be referred to as different conformations, conformations that correspond to local.
The conformation in which the newman projection shows all six hydrogens of ethane in plain view is a staggered conformation. Energy diagram for rotation about the cc bond in ethane. Two energetic extremes in the conformations of ethane are shown below, with the staggered conformation being lowest in energy most favored and the. Alkane stereochemistry concerns the stereochemistry of alkanes.
Identify whether each pair of compounds are constitutional isomers, stereoisomers, or identical. A conformation is a different arrangements of atoms in space produced by rotation about single bonds. Using the compute steric energy option under the mm2 menu, calculate the energy for the initial conformation of ethane. Conformational analysis of ethane energy diagram 24 the rotation around the cc single bond in ethane is not completely free because of the energy diferences between the staggered and eclipsed forms. Conformations of ethane ws10 questions key chem 211 dr. Rotational energy acts as a barrier in case of single bond rotation. Conformational analysis college of saint benedict and. As we know, ethane is not a flat molecule and to study its shape in detail we need to be able to represent the threedimensional structure on a flat surface.
Another clockwise rotation at an angle of 60 degrees would lead to second eclipsed conformation. Ethane is an alkane comprising of two carbon atoms. Molecular modeling and conformational analysis with pc. Eclipsed ethane has 12 kj per mol more energy than the staggered conformation. A molecule of ethane has only one type of each staggered and eclipsed conformation. In chemistry, conformational isomerism is a form of stereoisomerism in which the isomers can be interconverted just by rotations about formally single bonds refer to figure on single bond rotation. All staggered and eclipsed conformations of 1,2ethanediol, 2amino ethanol, and 1,2ethanediamine have been studied by the semiempirical. 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. It is approximately 12 kjmol 3 kcalmol more stable than the eclipsed, which is the least stable conformation. It is a colorless and odor gas at a standard temperature. For example, look at the staggered conformation of ethane. Accessing the configuration and conformation space of molecules configurations and conformations molecular networks most molecules can adopt more than one conformation of nearly equal energy by rotation around single bonds. These isomers are termed as conformational isomers.
A view of ethane seen by looking along the cc bond axis. In the case of the staggered conformation, the input file would be the following. The difference in energy between the staggered and eclipsed forms is due almost entirely to the torsional strain in the eclipsed conformation. How to analyze the staggered and eclipsed conformations of ethane. Conformations of organic molecules columbia university. Using chem3d pro build and minimize the ethane molecule. Newman projections and conformational isomers newman projections is a way to draw chemical conformations and views a carbon carbon chemical bond from front to back, front carbon as a dot and back carbon as a circle.
The solid line in the above figure represents the 6 carbonhydrogen bond that is extended at an angle of 120 degrees from 2 carbons. The newman projection corresponding to forms ad is shown below 58. Get a rough idea of the conformation of the molecule by minimizing the energy with the toolbar icon or use the dropdown menu build minimize. Torsional strain is the destabilization that results from eclipsed bonds. Rotation about the cc bond in ethane see the jsmol animation to the right produces different conformations. Lets start with a wedgedash view of the staggered conformation of ethane. Conformations are different arrangements of atoms that result from bond rotation. These are the lowest energy structure, called the staggered conformation, and the highest energy structure, called the eclipsed conformation. If youre seeing this message, it means were having trouble loading external resources on our website. Differing conformations of a molecule have different spatial arrangements of its atoms, obtained by torsion about one or more single bonds. Construct an explanation of why conformer a is called staggered and conformer b is called eclipsed. 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. There will be a change in the shape of the molecule when there is a rotation o.
It has no torsional strain as all the ch bonds are staggered to each other. Molecular modeling and conformational analysis with pc spartan. Illustration and interconversion of staggered and eclipsed ethane conformatiobs with space ffilling and ball stick models. Two in another plane in front of the paper and the remaining two in a. In the case of butane, however, two conformations are not enough to. 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. Carbon number name formula boiling point c melting point c c1methane ch4 164 182 c2 ethane ch3ch3 89 183 c3 propane ch3ch2ch3 42 190. Its chief use is as feedstock for ethylene production. Try rotating the 3d model of the animation so that you are looking directly along the. 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.
The differences in these two conformations for ethane can easily be seen by viewing them both on the screen simultaneously. So lets watch the video and look at the different conformations of ethane. Draw the staggered conformation of ethane chemistry. If youre behind a web filter, please make sure that the domains. Conformations of ethane ethane is an organic chemical compound. Circle the less energy more stable conformation above and explain the phenomenon that increases the energy of the other conformation. If we rotate this a little bit, well see the staggered conformation of ethane from a sawhorse. Rotate your ethane molecule so that one carbon atom is directly in front of the other carbon atom i. Barton britain and both were awarded nobel prize in 1969. Following steps 2 through 7, build another molecule of ethane. As ethane rotates toward an eclipsed conformation, its potential energy increases, and there is resistance to the rotation.
While holding down the alt key, click and hold down the left mouse button, drag the mouse to rotate about the cc bond to make your eclipsed conformation of ethane. There is a most important point to be kept in mind here. Organic chemistry university of california riverside. The true origin of ethanelike barriers can be found in another quantummechanical effect arising from the interactions of electron orbitals. Energy of eclipsed and staggered conformations of ethane. In the case of ethane, the staggered and eclipsed conformations can sufficiently describe the features of its conformational analysis. We know that ethane can exist in two conformations the staggered conformation and the eclipsed conformation. 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. Conformations of ethane experiments show that there is a 12 kjmol 2. There is growing awareness5 of the importance of hyperconjugative interactions between filled and unfilled orbitals in barrier phenomena. Conformational analysis of ethane what does a rotaional barrier of 12 kjmol mean.
The chair conformation is the most stable conformation of cyclohexane because all of the bond angles around the carbon atoms are at 109. Poutsma 1 worksheet 10 answer key conformations of ethane what is the overall 3d structure of ethane. This molecular mechanics energy minimization follows a very simple set of rules on how long typical bonds are and what conformation is lowest in energy. Conformation means the different arrangement of atoms in space that result from rotations of groups about a single bond. In a more complex molecule, such as butane, one can. 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. Conformations of ethane and butane conformational isomerism. Ethane h3cch3 and substituted ethane the ethane molecule, c2h6, can exist in both the staggered and eclipsed conformations where the staggered conformation is slightly more stable. What is the staggered conformation of ethane using the. The eclipsed conformation is destabilized by torsional strain. Names, formulas, boiling points, and melting points of c1 through c12 unbranched alkanes. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petrochemical byproduct of petroleum refining. The energetically staggered conformation is more stable than eclipsed conformation as in staggered conformation there is minimum repulsion on neighbouring h.
Organic chemistry computational modeling experiment. Would the eclipse conformation ever occur on its own. The ethane molecule, c2h6, can exist in both the staggered and eclipsed conformations where the staggered conformation is slightly more stable. Which points on the given energy diagram represents eclipsed confirmation of ethane and staggered confirmation of propane respectively. Conformations form when ethane rotates about one of its single covalent bond. In butane, the two staggered conformations are no longer equivalent and represent two. Torsional strain the eclipsed conformation of ethane is 12 kjmol less stable than the staggered.
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