Question

Draw the following. a. cis-2 -hexene b. trans- 2 -butene c. cis-2,3 -dichloro-2-pentene

Short answer

The short answer to drawing the given molecules is as follows: Cis-2-hexene: H H H | | | H-C-C=C-C-C-H \| | H H H Trans-2-butene: H H | | H-C=C-C-H | | H H Cis-2,3-dichloro-2-pentene: H H H | | | H-C-C=C-C-C-H Cl|Cl| H H H

Step-by-step solution

Understand cis and trans isomers

Cis and trans isomers are a way to describe the orientation of groups around a double bond. In the cis isomer, the two groups are on the same side of the double bond, while in the trans isomer, the two groups are on opposite sides of the double bond.

Draw cis-2-hexene

1. Begin by drawing a chain of six carbons, since "hex" refers to six. 2. Add a double bond between the second and third carbons, as indicated by "2" in the name. 3. The name indicates it is a cis isomer, so make sure two identical groups (hydrogens in this case) on carbons 2 and 3 are on the same side of the double bond. 4. Fill in the remaining hydrogens so that each carbon has a total of four bonds. 5. The final structure is: H H H | | | H-C-C=C-C-C-H \| | H H H

Draw trans-2-butene

1. Begin by drawing a chain of four carbons, since "but" refers to four. 2. Add a double bond between the second and third carbons, as indicated by "2" in the name. 3. This time, the name indicates it is a trans isomer, meaning the two hydrogens on carbons 2 and 3 should be on opposite sides of the double bond. 4. Fill in the remaining hydrogens so that each carbon has a total of four bonds. 5. The final structure is: H H | | H-C=C-C-H | | H H

Draw cis-2,3-dichloro-2-pentene

1. Start by drawing a chain of five carbons, as "pent" refers to five. 2. Add a double bond between the second and third carbons, as indicated by "2" in the name. 3. Since this is a cis isomer, make sure the identical groups (hydrogens in this case) on carbons 2 and 3 are on the same side of the double bond. 4. Add the chlorine atoms to carbons 2 and 3, as indicated by the "2,3-dichloro" part of the name. Carbons 2 and 3 would each have one hydrogen only, and the remaining hydrogens fill the other carbons so that each carbon has a total of four bonds. 5. The final structure is: H H H | | | H-C-C=C-C-C-H Cl|Cl| H H H

Key concepts

Organic Chemistry

Organic chemistry is a fascinating branch of chemistry focused primarily on the structure, properties, and reactions of carbon-containing compounds. These compounds are the building blocks of life and are incredibly diverse, forming the basis of everything from alcohols and acids to the DNA in our cells.
Organic molecules are often large and complex, composed of chains or other structures made of carbon atoms bonded to other elements such as hydrogen, oxygen, and chlorine. The backbone of these organic molecules often includes chains of carbon atoms, which can form rings and other shapes.
Understanding organic chemistry involves grasping the ways in which these compounds interact and change, including reactions such as polymerization or isomerization. Isomers are particularly interesting because they have the same molecular formula but different arrangements of atoms. This subtle difference in structure can lead to dramatically different properties, which is where our study of cis-trans isomers comes in.

Chemical Bonding

Chemical bonding is the process that holds atoms together in molecules. There are several types of chemical bonds, but in the case of cis-trans isomers, the focus is on covalent bonds, where atoms share electrons.
In organic molecules, covalent bonds can occur in single, double, or triple forms. Cis-trans isomerism, specifically, is a type of stereoisomerism that occurs in molecules with double bonds because these bonds prevent rotation. This lack of rotation means that the substituent groups attached to double-bonded carbons can either be on the same side, as in the cis isomer, or opposite sides, which is called the trans isomer.

• Cis Isomer: The same groups are on the same side of the double bond.
• Trans Isomer: The same groups are on opposite sides of the double bond.

This simple difference in the orientation of the groups leads to different physical and chemical properties, affecting boiling points, solubility, and even reactivity.

Molecular Structure

The molecular structure refers to the three-dimensional arrangement of atoms within a molecule, which determines the molecule's properties and behavior. In cis-trans isomers, the structure of the molecule around a double bond is key.
Double bonds are special because they involve the sharing of two pairs of electrons between two atoms, which makes them stronger and shorter than single bonds. The planar (flat) structure around the double bond is what allows for the existence of cis and trans isomers.
Understanding molecular structure is crucial in predicting the behavior of organic compounds, such as how they might react in a chemical reaction or interact with other substances. For example, in biological systems, these different isomers can have significantly different interactions with enzymes and receptors, leading to proteins behaving differently. This highlights the importance of molecular structure in both chemistry and biological contexts.