Question

Write the name and draw the structure of the alkyl group that corresponds to each of the following alkanes. a. methane b. butane c. octane

Short answer

a. Methane: The corresponding alkyl group is a methyl group (CH₃). Methyl Group Structure: ``` H | CH₃ ``` b. Butane: The corresponding alkyl groups are isopropyl (or isobutyl) and propyl (or n-butyl) groups. Isopropyl or Isobutyl Group Structure: ``` H H | | H - C - C | H ``` Propyl or n-butyl Group Structure: ``` H | H - C - C | H ``` c. Octane: The corresponding alkyl group is a heptyl group. Heptyl Group Structure: ``` H H H H H H H | | | | | | | H - C -C -C -C -C -C -C ```

Step-by-step solution

Understanding Alkanes and Alkyl Groups

An alkane is a saturated hydrocarbon containing only carbon (C) and hydrogen (H) atoms, with all the carbon atoms connected with single bonds (C-C) and each carbon atom connected to enough hydrogens to achieve four bonds in total. An alkyl group is derived from an alkane by removing a hydrogen atom from it.

Alkyl Group of Methane

Methane is the simplest alkane, with the molecular formula CH₄. As it consists of only one carbon atom and four hydrogen atoms, there is only one hydrogen atom to remove. When we remove one hydrogen from methane, we are left with a methyl group (CH₃), which is the alkyl group corresponding to methane.

Drawing the Structure of Methane and Methyl Group

Methane Structure: ``` H | CH₄ - C | H ``` Methyl Group Structure: ``` H | CH₃ ```

Alkyl Group of Butane

Butane is an alkane with the molecular formula C₄H₁₀. It has two possible alkyl groups, by removing one hydrogen atom from either one of the terminal carbon atoms or the internal carbon atoms: 1. Isopropyl group or isobutyl group, when removing hydrogen from an internal carbon. 2. Propyl group or n-butyl group, when removing hydrogen from a terminal carbon.

Drawing the Structure of Butane and Its Alkyl Groups

Butane Structure: ``` H H H H | | | | H - C-C-C-C - H | | | | H H H H ``` Isopropyl or Isobutyl Group Structure: ``` H H | | H - C - C | H ``` Propyl or n-butyl Group Structure: ``` H | H - C - C | H ```

Alkyl Group of Octane

Octane is an alkane with the molecular formula C₈H₁₈. Similar to butane, there can be various alkyl groups formed depending on the removal of hydrogen from different carbon atoms. However, we will focus on the simplest form, which is formed by removing a hydrogen atom from a terminal carbon.

Drawing the Structure of Octane and Its Alkyl Group

Octane Structure: ``` H H H H H H H H | | | | | | | | H - C -C -C -C -C -C -C -C - H | | | | | | | | H H H H H H H H ``` Heptyl Group Structure: ``` H H H H H H H | | | | | | | H - C -C -C -C -C -C -C ```

Key concepts

Alkanes and Alkyl Groups

Understanding the relationship between alkanes and alkyl groups is paramount in organic chemistry. Alkanes, often referred to as paraffins, are hydrocarbons that contain only single bonds between carbon atoms and have a general formula of C_nH_2n+2. They are the most basic structural form of hydrocarbons and exhibit a straightforward, saturated characteristic because they contain the maximum number of hydrogen atoms per carbon.

An alkyl group is essentially an alkane with one less hydrogen atom. This adjustment transforms the structure into a substituent, apt for attaching to other molecules. Alkyl groups retain the generic alkane structure but have an open bond where the hydrogen was removed. This open bond is where the alkyl group can bond to other atoms or groups of atoms in more complex molecules.

For instance, methane (CH₄) is the simplest alkane. If we remove one hydrogen atom, we end up with a methyl group (CH₃), identified by the prefix 'methyl' indicative of a single carbon alkyl group. When exploring longer chain alkanes, like butane (C₄H₁₀), we derive different alkyl groups by removing a hydrogen from various positions on the chain, such as the propyl (C₃H₇) or butyl (C₄H₉) groups.

Chemical Structures and Bonding

Delving into the realm of chemical structures and bonding provides insight into how atoms connect to form molecules. The bonding in alkanes revolves around single covalent bonds, where each atom shares a pair of electrons. Carbon atoms can form four such bonds due to their valency, leading to a three-dimensional tetrahedral shape around each carbon atom in alkanes.

Visualizing these structures helps in comprehending molecular shapes and potential reactive sites. For example, in a butane molecule, the carbon atoms are sequentially connected by single bonds with hydrogen atoms filling the remaining valence to satisfy the carbon's requirement for four bonds. When a hydrogen is removed to form an alkyl group, the remaining 'free' bond is where the alkyl group will attach to another molecule or atom, playing a critical role in synthetic chemistry.

The structures are drawn showing each carbon atom bonded to other carbons and to the necessary number of hydrogens to achieve full valency. Structural diagrams often use a zig-zag line where each point represents a carbon with implied hydrogen atoms completing the structure if not otherwise specified.

Hydrocarbons

The vast family of hydrocarbons, compounds made up of only hydrogen and carbon, are fundamental to organic chemistry and are categorized by the type of bonding between carbon atoms. Alkanes, with all single bonds, are termed saturated hydrocarbons because they 'saturate' carbon with hydrogen. In contrast, unsaturated hydrocarbons, such as alkenes and alkynes, have double or triple bonds and can accommodate additional hydrogen atoms.

Hydrocarbons are the backbone of many larger, more complex organic molecules and are critical ingredients in fuels, plastics, and pharmaceuticals. They are not only diverse in their molecular structures but also in their physical and chemical properties. For instance, the length and branching of a hydrocarbon chain can greatly affect its boiling point and solubility.

When discussing octane (C₈H₁₈), a component of gasoline, the carbon chain is longer and yields a heptyl group (C₇H₁₅) when a hydrogen atom is removed. This heptyl group, like all alkyl groups, points to the hydrocarbon's potential to interact and bind with other organic compounds, greatly diversified by the complexity inherent in hydrocarbon chains.