Question

Indicate whether each statement is true or false. (a) Butane contains carbons that are \(s p^{2}\) hybridized. (b) Cyclohexane is another name for benzene. (c) The isopropyl group contains three \(s p^{3}\)-hybridized carbons. (d) Olefin is another name for alkyne.

Short answer

(a) False - Butane contains \(sp^3\) hybridized carbons. (b) False - Cyclohexane is not another name for benzene; they are different compounds. (c) True - The isopropyl group contains three \(sp^3\)-hybridized carbons. (d) False - Olefin is another name for alkene, not alkyne.

Step-by-step solution

Statement (a)

: Butane is an organic compound with the formula C4H10 and contains four interconnected carbon atoms. The carbons in butane are tetrahedral, meaning that each carbon is surrounded by four sigma bonds. In such cases, carbon atoms are \(sp^3\) hybridized. Therefore, the statement is false, as it incorrectly says that butane has \(sp^2\) hybridized carbons.

Statement (b)

: Cyclohexane is an organic compound with the formula C6H12, while Benzene is an organic compound with the formula C6H6. Both compounds consist of six carbon atoms; however, their structures and chemical properties are different. Cyclohexane has a ring of six carbon atoms joined by single bonds (all carbons are \(sp^3\) hybridized), while benzene has a ring of six carbon atoms joined by alternating single and double bonds (all carbons are \(sp^2\) hybridized). Therefore, the statement is false, as cyclohexane and benzene are different compounds.

Statement (c)

: The isopropyl group (also known as the isopropyl radical or isopropylidene group) has the formula (CH3)2CH-. This group has three carbon atoms: two methyl groups (CH3) and one methylene group (CH2). All these carbon atoms are surrounded by four sigma bonds – three in the case of the methylene group, and four in the case of the methyl groups. As a result, all three carbons in the isopropyl group are \(sp^3\) hybridized. Therefore, the statement is true.

Statement (d)

: Olefin is another name for alkene, which is a hydrocarbon with at least one carbon-to-carbon double bond. An alkyne, on the other hand, is a hydrocarbon with at least one carbon-to-carbon triple bond. Since olefin refers to an alkene and not an alkyne, the statement is false.

Key concepts

Butane sp3 Hybridization

When studying butane, a molecule with the formula C4H10, it's critical to understand how the carbon atoms inside the molecule are bonded, a concept known as hybridization. Each carbon atom in butane forms four sigma bonds (single covalent bonds), which arrange themselves to maximize the distance between each other, ultimately creating a tetrahedral shape. This arrangement results from the hybridization of one 's' orbital and three 'p' orbitals in the carbon atom, leading to four equivalent atomic orbitals known as 'sp3' hybrid orbitals.

The misconception that butane contains 'sp2' hybridized carbons is linked to a misunderstanding of the molecule's geometry. 'Sp2' hybridization occurs when a carbon atom is involved in a double bond, which isn't the case for butane. Therefore, recognizing the 'sp3' hybridization of carbons in butane is fundamental in building a solid foundation in organic chemistry.

Cyclohexane and Benzene Structure Difference

Cyclohexane and benzene are both fundamental structures in organic chemistry, but they exhibit significant differences in molecular geometry and hybridization. Cyclohexane, with the formula C6H12, is a six-membered ring consisting only of single bonds between carbon atoms. In this structure, all carbon atoms are 'sp3' hybridized, leading to a non-planar geometry often represented in a chair-like conformation.

In contrast, benzene (C6H6) is known for its planar ring structure with alternating single and double bonds. This arrangement describes what chemists call resonance, giving benzene unique stability and chemical properties. The 'sp2' hybridization of carbons in benzene allows for the existence of a delocalized pi-system over the entire ring — a characteristic not seen in cyclohexane. Grasping these distinctions clarifies why cyclohexane and benzene, despite a similarity in the count of carbon atoms, are entirely different in their chemical behavior and reactivity.

Isopropyl Group Structure

The structure of an isopropyl group is essential knowledge when exploring the vast landscape of organic functional groups. An isopropyl group consists of three carbon atoms forming two methyl groups (CH3) and a central methylene group (CH2). Each carbon in this group is surrounded solely by sigma bonds, which is an indicator of 'sp3' hybridization.

This type of hybridization suggests that the carbons exhibit a tetrahedral geometry, emphasizing the importance of three-dimensional thinking when approaching organic structures. The compactness of the isopropyl group makes it a common substituent in organic molecules, providing a straightforward example of 'sp3' hybridized carbons at work. Recognizing and visualizing the isopropyl group within larger molecules is an invaluable skill for students learning organic chemistry.

Olefin vs Alkyne

The terms olefin and alkyne are often encountered in discussions on hydrocarbons; however, they refer to different types of compounds within organic chemistry. Olefins, synonymous with alkenes, are hydrocarbons containing at least one carbon-to-carbon double bond, characterized by 'sp2' hybridization. These carbon atoms share a sigma bond and a pi bond, resulting in a trigonal planar geometry around the double bonded carbons.

On the other hand, alkynes have at least one carbon-to-carbon triple bond. This bond entails one sigma and two pi bonds, leading to 'sp' hybridization and a linear geometry around the triple-bonded carbons. Understanding the difference between olefins and alkynes is not just about knowing their names; it is about recognizing the distinct structural, physical, and chemical properties that arise from the type of bonds present in these compounds.