Draw four compounds with molecular formula C₅H₁₀ that have carbon–carbon double bonds but do not have cis–trans isomers.

Verified step by step guidance

1. Step 1: Understand the molecular formula C5H10. This formula indicates that the compound is an alkene (CnH2n) due to the presence of a double bond, as it follows the general formula for alkenes.
2. Step 2: Recall that cis-trans isomerism occurs in alkenes when there are two different groups attached to each carbon of the double bond. To avoid cis-trans isomerism, ensure that at least one carbon in the double bond has two identical substituents.
3. Step 3: Begin by drawing a straight-chain alkene (pentene) where one of the double-bonded carbons has two identical substituents. For example, 2-methyl-1-butene has a double bond at the first carbon, and the second carbon has two hydrogens, preventing cis-trans isomerism.
4. Step 4: Create additional structures by varying the position of the double bond or branching the chain. For instance, 2-methyl-2-butene has a double bond at the second carbon, and the second carbon has two identical substituents (methyl groups), which also prevents cis-trans isomerism.
5. Step 5: Continue exploring other possibilities, such as cyclic alkenes like cyclopentene, where the ring structure inherently prevents cis-trans isomerism due to restricted rotation around the double bond. Another example is 3-methyl-1-butene, where the double bond is at the first carbon, and the third carbon has two hydrogens, avoiding cis-trans isomerism.

Key Concepts

Structural Isomers

Structural isomers are compounds that have the same molecular formula but differ in the connectivity of their atoms. In the case of C5H10, various structural isomers can be formed by altering the arrangement of carbon atoms and the placement of double bonds. Understanding structural isomerism is crucial for identifying different compounds that fit the same molecular formula.

Geometric Isomerism

Geometric isomerism, also known as cis-trans isomerism, occurs due to the restricted rotation around a double bond, leading to different spatial arrangements of substituents. For a compound to exhibit cis-trans isomerism, it must have two different groups attached to each carbon of the double bond. The question specifies compounds without cis-trans isomers, indicating that the double bonds must be positioned such that this type of isomerism is not possible.

Alkenes

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (C=C) and are characterized by their unsaturation. The presence of double bonds in alkenes allows for various structural configurations, but the specific arrangement of carbon atoms can lead to the absence of geometric isomers. Recognizing the properties and types of alkenes is essential for drawing the required compounds with the formula C5H10.