Write structural formulas for compounds that meet the following descriptions: a. An alkene, C 6 H 12 , that cannot have cis–trans isomers and whose longest chain is 5 carbons long

Welcome, everyone. Here's our next problem, provide the structural formula for an alkene with a molecular formula of C 10 H 20 does not exhibit a cist trans isomerism thick carbons as its longest chain and is symmetrical. We've got a lot of conditions to fulfill here. Let's just take them one at a time and fill in our structural formula. Well, the simplest place to start, we have an keen, so we know we've got one cc double bond. So lets fill that in our molecular formula of C 10 H 20 tells us that we have only one double bond. As we know, we can look at the formula CNH two N plus two for an alkane. And in this case, that would be C 10 H 22. If it were an Alcaine, it's only H 20. So we have a single, either double bond or ring. We know where it's an alkene. We know we have a double bond, but there will only be one will then go to six carbons as its longest chain. So let's start with and we need it to be symmetrical. So we need it to be the same on either side. So let's look at putting a bond on either side and adding some more carbons. So we'll add a carbon on either side, vit tour double bond carbons. Now we have 1234 carbons. So each one just needs one more. Again, we have to add one on each side to keep this being a symmetrical molecule. So now we have six carbons, we cannot get any longer with this chain. It's symmetrical on both sides. However, we've still got two more conditions to fill. We need four more carbons and we cannot have cyst trans isomerism. That means that on at least one of our sides, the two R groups must be identical. But since our molecules to be symmetrical are remaining to uh the groups coming off of our double bond must be identical on both sides as well as on the same side. Since we have four carbons left, the simple solution is two carbons on either side. So we essentially have a double bond between two carbons and our four groups are all ethyl groups. So this gives us no cistron isomerism completely symmetrical and six carbons is our longest chain. We essentially have 26 carbon chains here. So now we just need to fill in our hydrogens to get a structural formula. So each of our terminal hydrogen, terminal carbons, excuse me gets three hydrogens note that now we have 12 hydrogens and then our four single bonded internal carbons will get two hydrogens each, which will give us the remaining eight hydrogens, our carbons in the double bond. Of course, don't have any more bonds and they have no hydrogens. Let me just fill in the rest of the hydrogens. So we've now drawn the structural formula or a molecule that fills all of these parameters. We have a hexen, six carbons, that would be a three hexen. We're just going to write the names to give a good description of this. A three hexen and then two ethyl groups coming off of carbons, three and four. So it would be three comma four die ethel, the hexen being the molecule we're looking for. See you in the next video.

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13. Alkenes, Alkynes, and Aromatic Compounds

Isomers

GOB Chemistry

13. Alkenes, Alkynes, and Aromatic Compounds

Isomers

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Problem 35a

Textbook Question

Write structural formulas for compounds that meet the following descriptions:
a. An alkene, C₆H₁₂, that cannot have cis–trans isomers and whose longest chain is 5 carbons long

Verified step by step guidance

Step 1: Understand the requirements of the problem. The compound is an alkene (contains a carbon-carbon double bond) with the molecular formula C6H12. It cannot have cis-trans isomers, which means the double bond must be located in such a way that identical groups are attached to the same carbon atom of the double bond.

Step 2: Recall that cis-trans isomerism occurs when the two carbons in the double bond each have two different groups attached. To prevent cis-trans isomerism, ensure that one of the carbons in the double bond has two identical groups attached.

Step 3: Consider the structural requirement that the longest chain is 5 carbons long. This means the main chain of the molecule should have 5 carbons, and the sixth carbon will be part of a substituent group.

Step 4: Draw the structure of the compound. Start with a 5-carbon chain and place the double bond in a position where one of the carbons in the double bond has two identical groups (e.g., two hydrogens). Add the sixth carbon as a substituent group to complete the molecular formula C6H12.

Step 5: Verify the structure. Ensure the molecular formula matches C6H12, the compound is an alkene, the longest chain is 5 carbons, and the double bond does not allow for cis-trans isomerism. Adjust the structure if necessary to meet all criteria.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Alkene

An alkene is a type of hydrocarbon that contains at least one carbon-carbon double bond (C=C). Alkenes are unsaturated compounds, meaning they have fewer hydrogen atoms than alkanes with the same number of carbon atoms. The presence of the double bond gives alkenes unique chemical properties and reactivity, making them important in organic chemistry.

Cis-Trans Isomerism

Cis-trans isomerism, also known as geometric isomerism, occurs in alkenes due to the restricted rotation around the double bond. In cis isomers, substituents are on the same side of the double bond, while in trans isomers, they are on opposite sides. For a compound to exhibit cis-trans isomerism, it must have two different substituents on each carbon of the double bond, which is not possible in certain structures.

Longest Carbon Chain

The longest carbon chain in a hydrocarbon is the continuous chain of carbon atoms that contains the most carbon atoms. Identifying the longest chain is crucial for naming the compound according to IUPAC nomenclature and determining its structural features. In the context of alkenes, the longest chain also influences the position of the double bond and the potential for isomerism.

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