Question

Draw structural formulas for three isomeric alkanes having the formula \(\mathrm{C}_{6} \mathrm{H}_{14}\)

Short answer

Three isomeric alkanes with the molecular formula \(\mathrm{C}_{6} \mathrm{H}_{14}\) are n-hexane, 2-methylpentane, 3-methylpentane, and 2,3-dimethylbutane.

Step-by-step solution

Draw the Base Structure of the Alkane

The base structure of an alkane is a straight chain of carbon-carbon single bonds, with hydrogen atoms bonded to each carbon atom to complete the tetravalency of carbons. Since the alkane has a formula of \(\mathrm{C}_{6} \mathrm{H}_{14}\), there are 6 carbon atoms and 14 hydrogen atoms. The base structure will have six carbon atoms in a straight chain, with each carbon atom bonded to the appropriate number of hydrogen atoms. The straight-chain structure is called n-hexane.

Create the First Isomer

We will create the first isomer by rearranging the carbon atoms. We do this by shortening the main chain by one carbon atom (to 5 carbons) and adding a branch with 1 carbon atom. This is called 2-methylpentane because the extra carbon or "methyl group" is attached to the second carbon atom in the pentane chain.

Create the Second Isomer

For the second isomer, we will keep the main chain at 5 carbons but rearrange the position of the branched methyl group. If we move the methyl group to the third carbon in the chain, this creates a new isomer called 3-methylpentane.

Create the Third Isomer

The last isomer involves shortening the main chain of carbon atoms to 4 and creating two branches, each containing one carbon atom. This is called 2,3-dimethylbutane, as there are two methyl groups attached at the second and third carbon atoms in the butane chain. In conclusion, three isomeric alkanes with the molecular formula \(\mathrm{C}_{6} \mathrm{H}_{14}\) are n-hexane, 2-methylpentane, 3-methylpentane, and 2,3-dimethylbutane.

Key concepts

Structural Formulas

When studying chemistry, the structural formula of a compound is a crucial tool that provides information about the arrangement of atoms within the molecule. In the case of alkanes, which are hydrocarbons that contain single covalent bonds, structural formulas become essential to understanding the different ways in which a molecule can be organized.

For example, considering an alkane with the chemical formula \( \mathrm{C}_{6} \mathrm{H}_{14} \), the structural formula is not only about the numbers of carbon (C) and hydrogen (H) atoms, but also about how they are connected to each other. Structural formulas give insight into the molecule's geometry, revealing whether the carbon atoms form a straight chain or if some are arranged as branches. This makes structural formulas invaluable in visualizing and differentiating between various isomers of the same molecular formula.

These visual representations include notations such as lines for chemical bonds and symbols for atoms, making them somewhat like a map that guides you through the molecular structure. By understanding and being able to interpret these formulas, students can predict physical and chemical properties of the compounds and, hence, their potential reactions and uses in different chemical contexts.

Alkane Isomers

Alkane isomers are compounds that have the same molecular formula but differ in the structure of their carbon skeleton. Due to the versatile nature of carbon atoms to form chains and rings of different lengths and arrangements, alkanes can exist in numerous isomeric forms.

For instance, the molecular formula \( \mathrm{C}_{6} \mathrm{H}_{14} \) represents several different isomers. The simplest is called the 'straight-chain' or 'normal' alkane, where all carbon atoms are connected in a sequential linear fashion. This structure, referred to as n-hexane, serves as the base from which other isomers, or 'branched' alkanes, can be derived.

Creating alkane isomers involves rearranging the carbon atoms to make different structures - for example, moving a carbon atom from the main chain to create a branch. This process results in various isomers, such as 2-methylpentane and 3-methylpentane, where the numbers indicate the position of the branch in the carbon chain. Isomers have unique physical and chemical properties, providing diverse applications in the field of organic chemistry.

Chemical Nomenclature

Chemical nomenclature, the standardized system for naming chemical substances, allows chemists to communicate the structure and composition of compounds clearly and concisely. In organic chemistry, the nomenclature of alkanes follows specific rules set by the International Union of Pure and Applied Chemistry (IUPAC).

When naming an alkane, you begin with the name of the longest continuous carbon chain, which gives you the base name of the compound. Prefixes are then added to indicate the presence and positioning of any branches, or alkyl groups, branching off of the main chain. The positions of these groups are denoted by numbers, which minimizes ambiguity and ensures that each compound has a unique name.

The names of the isomers of \( \mathrm{C}_{6} \mathrm{H}_{14} \) follow these rules. The compound with no branches is called n-hexane. When a methyl group (a single carbon branch) is added, the name changes to reflect its position, resulting in names like 2-methylpentane and 3-methylpentane. A compound with two methyl groups would be named with both numbers and the prefix 'di-' to indicate two, as in 2,3-dimethylbutane. Mastery of this naming system is essential, as it allows the clear differentiation and identification of compounds with complex structures.