Question

Draw the structural formulas for three isomers of pentane, \(\mathrm{C}_{5} \mathrm{H}_{12}\).

Short answer

The three isomers of pentane \(\mathrm{C}_{5}\mathrm{H}_{12}\) are: 1. n-pentane: H H H H H | | | | | C-C-C-C-C | | | | | H H H H H 2. isopentane (2-methylbutane): H | H-C-H | H-C-C-C-C | | | H H H H H 3. neopentane (2,2-dimethylpropane): H H H | | | H-C-C-C-C | | H H H

Step-by-step solution

Draw the first isomer (n-pentane)

For the first isomer, let's arrange the carbon atoms in a straight chain. With 5 carbon atoms, this is called normal or n-pentane. To maintain the molecular formula, each carbon atom should also have the appropriate number of hydrogen atoms. In the case of n-pentane, the number of hydrogen atoms on each carbon atom is: - Carbon 1 and 5: 3 Hydrogen atoms - Carbon 2, 3, and 4: 2 Hydrogen atoms Here is the structural formula of n-pentane: H H H H H | | | | | C-C-C-C-C | | | | | H H H H H

Draw the second isomer (isopentane or 2-methylbutane)

For the second isomer, let's arrange the carbon atoms with 4 carbon atoms in a straight chain and 1 carbon atom branching off. In this case, we can place the branching carbon atom on the second carbon atom in the chain. This isomer is known as isopentane or 2-methylbutane. The number of hydrogen atoms on each carbon atom is: - Carbon 1 and 4: 3 Hydrogen atoms - Carbon 2: 1 Hydrogen atom - Carbon 3: 2 Hydrogen atoms - Carbon branching from Carbon 2: 3 Hydrogen atoms Here is the structural formula of isopentane: H | H-C-H | H-C-C-C-C | | | H H H H H

Draw the third isomer (neopentane or 2,2-dimethylpropane)

For the third isomer, let's arrange 3 carbon atoms in a straight chain and then have 2 carbon atoms branching off from the central, second carbon atom. This isomer is called neopentane or 2,2-dimethylpropane. The number of hydrogen atoms on each carbon atom is: - Carbon 1 and 3: 3 Hydrogen atoms - Carbon 2: 0 Hydrogen atoms - Two carbon atoms branching from Carbon 2: 3 Hydrogen atoms each Here is the structural formula of neopentane: H H H | | | H-C-C-C-C | | H H H These are the three structural formulas for the isomers of pentane: n-pentane, isopentane (2-methylbutane), and neopentane (2,2-dimethylpropane).

Key concepts

Structural Formulas

Understanding structural formulas is key to visualizing how the atoms in a molecule are arranged. These formulas provide a two-dimensional representation of how the atoms are bonded in a molecule. For example, in the case of pentane (\(C_5H_{12}\)), we have a molecule made up of carbon (\(C \)) and hydrogen (\(H\)) atoms. The carbon atoms can be arranged in different ways to form structures known as isomers.

Isomers have the same molecular formula but differ in the arrangement of their atoms, leading to distinct properties. In structural formulas, lines represent chemical bonds, with each line indicating a bond between two atoms. A single line signifies a single bond, which is a pair of shared electrons between atoms. The structural formulas for the isomers of pentane all adhere to the general formula\(C_5H_{12}\), but each isomer has a unique arrangement of carbon atoms.

Let's consider the structural formula of n-pentane. It has a linear arrangement of carbon atoms, resulting in a 'straight chain'. When we move on to isopentane or 2-methylbutane, we see a branch in the carbon chain. This changes the structure, but not the molecular formula. Finally, neopentane or 2,2-dimethylpropane, features even more branching, with two carbon atoms connecting to the central carbon, forming a more compact structure.

Carbon Chain

The term 'carbon chain' refers to the arrangement of carbon atoms within a molecule. In organic chemistry, the structure of carbon chains is fundamental to the molecule's identity and properties. Carbon atoms have the unique ability to bond with each other in long chains and rings, which provides the backbone for a vast number of organic compounds.

In the context of pentane isomers, we can observe various types of carbon chains. In n-pentane, the carbon atoms form a 'straight chain', meaning they are connected in a continuous line without branches. Conversely, isopentane introduces a 'branched chain', where a carbon atom extends from the main sequence, altering the molecule's shape and properties. Neopentane pushes this even further with a more complex branched structure, with the central carbon atom bonding to four others.

Importance of Carbon Chain Variation

The variation in carbon chains is crucial because it changes the compound's physical and chemical characteristics. For instance, branching usually results in lower boiling points because branched molecules can't pack as closely together as straight-chain molecules, leading to weaker intermolecular forces. Therefore, when learning organic chemistry, mastering the implications of carbon chain variations on molecular behavior is essential.

Molecular Formula

The molecular formula of a compound provides a succinct way of expressing the number and type of atoms present in a molecule. For instance, pentane has the molecular formula\(C_5H_{12}\), indicating it contains five carbon atoms and twelve hydrogen atoms.

The molecular formula is vital for understanding the compound's basic composition but doesn't reveal the arrangement of those atoms. This is where structural formulas and the concept of isomerism come into play. Despite having the same molecular formula, isomers can display vastly different chemical behaviors and physical properties.

A Closer Look at \(C_5H_{12}\) Isomers

In the case of the isomers of pentane, they all share the molecular formula \(C_5H_{12}\) but have distinct structural formulas. This is a classic example of structural isomerism, where the connectivity of atoms differs. In educational settings, students are often tasked with drawing structural formulas for a given molecular formula, which tests their understanding of how atoms can be rearranged while keeping the overall composition constant. Remember, the molecular formula is just the beginning; the real chemistry opens up when exploring the diversity of structures it can represent.