Oil is a mixture of liquid alkanes and other hydrocarbons. Why do halogenation reactions take place only at high temperatures or in the presence of light? Methane : It is a colorless and odorless gas produced abundantly in nature and as a product of certain human activities. To satisfy the second rule, we want to choose the numbering scheme that provides the lowest possible numbering of this substitute. Because the two substitutes are identical, neither takes alphabetical precedence with respect to numbering the carbons. • The hydrocarbon meaning is that these compounds exclusively consist of hydrogen and carbon atoms. For example, isopentane, neopentane, and n-pentane are names of branched forms of the alkane pentane. The longest carbon chain has been highlighted in red and consists of seven carbons. The very first five alkane formulas with an unbranched chain are shown below: Formulas of organic compounds provide the information of different properties and structures of those compounds. To select the correct numbering scheme, we need to utilize the third rule. Similar to the alkyl groups above, the concept of naming alkoxides can be applied to any of the straight chain alkanes provided in the table above. Consider the following representations of the molecule propane: Figure 2: Full structure of propane and skeletal structure of propane. Rule #2: Carbons bonded to a functional group must have the lowest possible carbon number. methylene in the central portion of the chain. In drawing hydrocarbons, it can be time-consuming to write out each atom and bond individually. The molecular formula of C. may even be applied to many alkanes, each of which has unique physical, chemical , and toxicological properties. Propane (C3H8) 4. Structural isomers have a lesser boiling point as compared to their equivalent straight-chain alkanes. Progressively longer hydrocarbon chains can be made and are named systematically, depending on the number of carbons in the longest chain. The longest carbon chain has been highlighted in red and consists of seven carbons. After taking functional groups into consideration, any substitutes present must have the lowest possible carbon number. Simple alkane methane contains one carbon atom and four hydrogen atoms, and CH, is its molecular formula. The melting point increases as the molecular weight of the alkane increases. Examples: The prefix neo- refers to a substituent whose second-to-last carbon of the chain is trisubstituted (has three methyl groups attached to it). The principle of homology allows us to write a general formula for alkanes: C n H 2 n + 2. Consider the following representation of the molecule methane: Figure 1: Two dimensional representation of methane. In the tetrahedral geometry, only two bonds can occupy a plane simultaneously. isopentane which is the same as 2-methylbutane, isobutane which is the same as 2-methylpropane. Missed the LibreFest? Straight-chain alkanes are sometimes indicated by the prefix n- (for normal) to distinguish them from branched-chain alkanes having the same number of carbon atoms. Compounds with the same molecular formula, and yet distinct structural formulas are known as structural isomers of that compound. Nonane (C9H20) 10. The prefix will be placed in front of the alkane name that indicates the total number of carbons. In a skeletal structure, only the bonds between carbon atoms are represented. Since, in the absence of double or triple bonds, carbon makes four bonds total, the presence of hydrogens is implicit. If we number the chain from the right, chlorine, the methyl group and bromine would occupy the second, third and sixth positions, respectively, which is illustrated in the first drawing below. The eight-carbon alkane has a molecular formula like C8H18 and a structural formula as shown in the image below. Butane (C4H10) 5. Cloudflare Ray ID: 5f7b1ee10bdd747a Does radical halogenation only occur in alkanes? Rule #1: Choose the longest, most substituted carbon chain containing a functional group. This Alkyl group is very often referred to as the letter R, the same as the halogens, which are represented by the letter X. This is because in the tetrahedral geometry all bonds point as far away from each other as possible, and the structure is not linear. What do the pathway and stoichiometry of halogenation depend on? Heptane (C7H16) 8. 3549 views This equation describes the relationship between the number of hydrogen and carbon atoms in alkanes: where "C" and "H" are used to represent the number of carbon and hydrogen atoms present in one molecule. Just like other organic compounds, carbon atoms in alkanes will also form straight chains, branched chains, or rings. In the first drawing, the methyl occupies the third position. As a matter of fact, alkanes are hydrophobic in nature, which means that alkanes are insoluble in water. In this example, numbering the chain from the left or the right would satisfy this rule. This example contains two functional groups, bromine and chlorine, and one substitute, the methyl group. 2. Ethane (C2H6) 3. CH 3-CH 3 + Br 2 → CH 3-CH 2-Br + HBr. Pro Lite, CBSE Previous Year Question Paper for Class 10, CBSE Previous Year Question Paper for Class 12. These characteristics are due to strong repulsive forces generated between electrons on neighboring atoms, which are in close proximity in crystalline solids. Each atom is bonded to adequate hydrogen atoms to form a total of 4 single covalent bonds. Name each side chain according to its number of … It will be important to familiarize yourself with these names because they will be the basis for naming many other organic molecules throughout your course of study. Examples of alkanes 1- Linear Alkanes . Also, the even-numbered alkanes are packed tightly in the solid phase, establishing a very well-organized structure that is difficult to break down. Certain branched alkanes have common names that are still widely used today. For example, if the carbon atom makes only one explicit bond, there are three hydrogens implicitly attached to it. (For this formula look to the "n" for the number, the "C" and the "H" letters themselves do not change.). The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot.