Question

For each of the following straight-chain alkanes, draw the structural formula. a. heptane b. nonane c. propane d. decane

Short answer

a. Heptane: \(CH_3-CH_2-CH_2-CH_2-CH_2-CH_2-CH_3\) b. Nonane: \(CH_3-CH_2-CH_2-CH_2-CH_2-CH_2-CH_2-CH_2-CH_3\) c. Propane: \(CH_3-CH_2-CH_3\) d. Decane: \(CH_3-CH_2-CH_2-CH_2-CH_2-CH_2-CH_2-CH_2-CH_2-CH_3\)

Step-by-step solution

Identify the number of carbon atoms in each alkane

According to the names of each alkane, we can determine the number of carbon atoms: a. Heptane: 7 carbon atoms (hept- indicates 7) b. Nonane: 9 carbon atoms (non- indicates 9) c. Propane: 3 carbon atoms (prop- indicates 3) d. Decane: 10 carbon atoms (dec- indicates 10)

Draw the structural formulas

We will draw the structural formulas of each alkane by placing the carbon atoms in a straight chain and attaching the corresponding hydrogen atoms to fulfill the valency of each carbon atom. a. Heptane: \(CH_3-CH_2-CH_2-CH_2-CH_2-CH_2-CH_3\) b. Nonane: \(CH_3-CH_2-CH_2-CH_2-CH_2-CH_2-CH_2-CH_2-CH_3\) c. Propane: \(CH_3-CH_2-CH_3\) d. Decane: \(CH_3-CH_2-CH_2-CH_2-CH_2-CH_2-CH_2-CH_2-CH_2-CH_3\)

Key concepts

Introduction to Organic Chemistry

Organic chemistry is the study of the structure, properties, composition, reactions, and synthesis of organic compounds that contain carbon. These compounds form the basis of life on Earth and are central to the petrochemical industry, pharmaceuticals, and many other areas. In organic chemistry, the focus is on carbon atoms and their interactions with other elements, primarily hydrogen, oxygen, nitrogen, and sometimes sulfur and halogens.

Hydrocarbons, which are compounds consisting solely of carbon and hydrogen, are the simplest organic compounds. Among these, alkanes are particularly important as they are saturated hydrocarbons with single bonds between carbon atoms. Their general formula is given by C_nH_2n+2, where n is the number of carbon atoms. The structural formulas of alkanes show how these atoms are bonded, and provide insight into the compound's reactivity and physical properties.

Alkane Structure and Representation

Alkanes are made up of carbon atoms connected in a chain with single bonds and surrounded by hydrogen atoms. While they can have straight or branched chains, the exercise focuses on straight-chain alkanes. The structural formula of an alkane provides a visual representation of the molecule, showing how the carbon atoms bond together and how hydrogen atoms are connected to the carbon skeleton.

When drawing a structural formula, we start with the carbon backbone. Each carbon atom forms four bonds. In a straight-chain alkane, the internal carbon atoms will form single bonds with two other carbons and two hydrogens (CH₂), while the carbon atoms at the ends of the chain will bond with three hydrogens and one other carbon (CH₃). By following these rules, we create a clear depiction of the molecule, showcasing the connectivity and arrangement of atoms.

Chemical Nomenclature of Alkanes

Chemical nomenclature is a systematic method for naming chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). It provides a unique and unambiguous name for each compound based on its structure. For alkanes, the prefixes such as 'meth-', 'eth-', 'prop-', and so forth indicate the number of carbon atoms (one, two, three, respectively), while the '-ane' suffix denotes that the compound is an alkane, meaning all the bonds between carbon atoms are single bonds.

In the provided exercise, the use of prefixes like 'hept-' for seven carbons and 'dec-' for ten carbons follows the systematic nomenclature. By learning the rules of nomenclature and prefix meanings, students can not only name alkanes correctly but also infer the number of carbon atoms in the chain based on the compound's name. Understanding these fundamentals of naming creates the foundation for further learning in organic chemistry.