Introduction to Organic Compounds

Introduction to Organic Compounds: Hydrocarbons Prelab Problems: 1. What elements are present in alkanes? 2. Would you expect hexane to be soluble in water? Why? 3. Which is more flammable, hexane or potassium sulfide? 4. Why are 1-chlorobutane and 2-chlorobutane structural isomers? 5. Draw the condensed structural formula for each of the following: a) 2,3-dimethylpentane b) 1,4-dichlorocyclohexane 6. Write the reaction for the hydrogenation of 2-methyl-1-pentene in the presence of a nickel catalyst and name the product. IUPAC name of the product: 7. Write the reaction for when ~butene reacts with Cl2 and name the product formed. IUPAC name of the product:

The Correct Answer and Explanation is:

Answers to Prelab Problems – Introduction to Organic Compounds: Hydrocarbons

1. What elements are present in alkanes?
   Alkanes are composed only of carbon (C) and hydrogen (H) atoms.
2. Would you expect hexane to be soluble in water? Why?
   No, hexane is not soluble in water because hexane is a nonpolar hydrocarbon, while water is a polar molecule. The principle “like dissolves like” means that polar substances dissolve in polar solvents, and nonpolar substances dissolve in nonpolar solvents.
3. Which is more flammable, hexane or potassium sulfide?
   Hexane is more flammable than potassium sulfide. Hexane is a volatile organic compound that easily vaporizes and combusts in air, while potassium sulfide is an ionic compound and not flammable under normal conditions.
4. Why are 1-chlorobutane and 2-chlorobutane structural isomers?
   1-chlorobutane and 2-chlorobutane are structural isomers because they have the same molecular formula (C₄H₉Cl) but different connectivity of atoms. In 1-chlorobutane, the chlorine is attached to the first carbon, whereas in 2-chlorobutane, the chlorine is bonded to the second carbon atom.
5. Draw the condensed structural formula for each of the following: a) 2,3-dimethylpentane:
   CH3-CH(CH3)-CH(CH3)-CH2-CH3 b) 1,4-dichlorocyclohexane:
   Cl-CH2-(CH2)4-CH2-Cl (in cyclic form, chlorine atoms are on carbon 1 and carbon 4 of a cyclohexane ring)
6. Write the reaction for the hydrogenation of 2-methyl-1-pentene in the presence of a nickel catalyst and name the product.
   Reaction:
   C₆H₁₂ (2-methyl-1-pentene) + H₂ → C₆H₁₄ (in presence of Ni catalyst)
   IUPAC name of the product: 2-methylpentane
7. Write the reaction for when butene reacts with Cl₂ and name the product formed.
   Reaction:
   C₄H₈ (butene) + Cl₂ → C₄H₈Cl₂
   Product formed: 1,2-dichlorobutane (if 1-butene is used)
   IUPAC name of the product: 1,2-dichlorobutane

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Explanation

Hydrocarbons are organic compounds composed entirely of carbon and hydrogen. They are classified into alkanes (single bonds), alkenes (at least one double bond), and alkynes (at least one triple bond). Alkanes, such as methane and hexane, are saturated hydrocarbons with only single covalent bonds. The elements present in alkanes are solely carbon and hydrogen, making them nonpolar molecules. Due to their nonpolar nature, alkanes like hexane are not soluble in polar solvents such as water. Instead, they dissolve in nonpolar solvents.

Flammability is an important physical property of hydrocarbons. Hexane is highly flammable due to its low boiling point and ability to form combustible vapors. In contrast, inorganic compounds like potassium sulfide do not easily vaporize and are not considered flammable under normal conditions.

Isomerism is a key concept in organic chemistry. Structural isomers, like 1-chlorobutane and 2-chlorobutane, differ in the arrangement of their atoms despite having the same molecular formula. This difference in structure often leads to variations in physical and chemical properties.

Understanding the structure of molecules is vital. For example, 2,3-dimethylpentane is a branched alkane, and 1,4-dichlorocyclohexane is a substituted cycloalkane with chlorine atoms on opposite sides of a six-membered ring.

Chemical reactions such as hydrogenation convert alkenes to alkanes. For example, hydrogenating 2-methyl-1-pentene yields 2-methylpentane. Similarly, addition reactions like the reaction of butene with chlorine form dihaloalkanes such as 1,2-dichlorobutane. These reactions highlight the reactivity of the double bond in alkenes and how functional groups alter compound properties.

Understanding these principles is essential for grasping the basics of organic chemistry and hydrocarbon behavior.