Introduction to Organic Chemistry: Hydrocarbons

General Introduction to Organic Chemistry: Hydrocarbons

12.1 Organic Compounds

• Organic chemistry is defined as the study of carbon compounds.

• Characteristics of Organic Compounds:

  • Contain carbon and hydrogen, often along with other nonmetals like oxygen, sulfur, nitrogen, phosphorus, or halogens.

  • Found in products such as gasoline, medicines, shampoos, plastics, and perfumes.

• Functional Groups:

  • Organic compounds are classified based on functional groups, which dictate similar physical and chemical properties within the group.

Properties of Organic Compounds

• Covalent Bonds: Organic compounds typically exhibit covalent bonding.

• Melting and Boiling Points: Generally have low melting (e.g., $-188 ext{ °C}$ for propane) and boiling points (e.g., $-42 ext{ °C}$ for propane).

• Flammability: These compounds are highly flammable and easily undergo combustion.

• Solubility in Water: Organic compounds usually are not soluble in water unless they contain a polar group, contrasting with many inorganic compounds.

Comparison of Organic and Inorganic Compounds

• Table 12.1 (Properties of Organic vs Inorganic Compounds):

  • Elements Present:

    • Organic: C and H, possibly O, S, N, P, or Cl (F, Br, I)

    • Inorganic: Typically metals and nonmetals

  • Particles:

    • Organic: Molecules (e.g., C3H8)

    • Inorganic: Mostly ionic (e.g., $NaCl$)

  • Bonding:

    • Organic: Mostly covalent

    • Inorganic: Many ionic, some covalent

  • Polarity of Bonds:

    • Organic: Nonpolar unless a strongly electronegative atom is present

    • Inorganic: Most ionic or polar covalent

  • Melting and Boiling Points:

    • Organic: Usually low, e.g., $-188 ext{ °C}$ and $-42 ext{ °C}$

    • Inorganic: Usually high, e.g., $801 ext{ °C}$ and $1413 ext{ °C}$

  • Flammability:

    • Organic: High

    • Inorganic: Low

  • Solubility in Water:

    • Organic: Not soluble unless polar

    • Inorganic: Usually soluble unless nonpolar

Learning Check 1

• Characteristics of compounds to identify as organic or inorganic:

  • A. High melting point: Inorganic

  • B. Not soluble in water: Organic

  • C. Contains carbon and hydrogen: Organic

  • D. Formula$MgCl_2$ : Inorganic

  • E. Burns easily in air: Organic

Representations of Organic Compounds

• Hydrocarbons: Organic compounds with primarily carbon and hydrogen.

  • Each carbon in organic molecules forms four bonds.

  • Methane (CH₄) Representation: Three-dimensional and two-dimensional representations include:

    • (a) space-filling model

    • (b) ball-and-stick model

    • (c) wedge–dash model

    • (d) expanded structural formula

    • (e) condensed structural formula

Carbon Compounds: Methane (CH₄)

• Chemical Structure:

  • Expanded structural formula shows all atoms and their bonds.

  • Condensed structural formula groups carbon atoms with attached hydrogen units.

  • Methane performs as a tetrahedral with bond angles of $109°$ and exhibits saturated hydrocarbon characteristics (only single bonds).

Carbon Compounds: Ethane (C₂H₆)

• Structural Characteristics:

  • Each carbon forms three covalent bonds to hydrogen and one to another carbon.

  • Various representations include 3D models and structural formulas similar to methane.

Learning Check 2

• For butane (C₄H₁₀), predict the shape around each carbon atom: Each carbon exhibits a tetrahedral shape due to four single covalent bonds.

12.2 Alkanes

• Overview: Alkanes have strong covalent bonds that allow for extensive and stable carbon chains to be formed, referenced with propane (C₃H₈).

• Learning Goal: Write IUPAC names and draw structural formulas for alkanes and cycloalkanes.

Alkanes

• Characteristics:

  • Formed via a continuous chain of carbon atoms.

  • Named using IUPAC system (International Union of Pure and Applied Chemistry).

  • Names end in '-ane'.

  • Utilize Greek prefixes for carbon chains with five or more members.

IUPAC Names of Alkanes

• Alkanes with five or more carbon atoms utilize Greek prefixes:

  • pent (5), hex (6), hept (7), oct (8), non (9), dec (10).

Table 12.2: IUPAC Names and Formulas of the First 10 Alkanes

Structural Formulas of Butane (C₄H₁₀)

• Expanded Structural Formula: 4-carbon chain with 2 central carbons each bonded to 2 hydrogens, whereas the end carbons bond to 3 hydrogens each.

• Line-Angle Formulas:

  • Two configurations forming 4 line segments with 3 angles.

Conformations of Alkanes

• Carbon atoms in a continuous chain can rotate, enabling several different arrangements for the attached groups.

Cycloalkanes

• Definitions and Characteristics:

  • Cyclic Alkanes have two fewer hydrogen atoms than their open chain counterparts.

  • Named by prefixing 'cyclo' before the corresponding alkane name of the same carbon count (e.g., propane (C₃H₈) becomes cyclopropane (C₃H₆)).

Formulas of Cycloalkanes

Table 12.4

• Illustrates the structures and chemical formulas of various cycloalkanes including cyclopropane, cyclobutane, cyclopentane, and cyclohexane.

Learning Check 1

• Provide IUPAC names for given alkane structures:

  • A. Alkane with eight continuous carbon atoms: Octane

  • B. Cyclic molecule with five carbon atoms: Cyclopentane

12.3 Alkanes with Substituents

• When alkanes have four or more carbon atoms, side groups (substituents) can attach to the carbon chain.

• Learning Goal: Write IUPAC names for alkanes with substituents along with their structural formulas.

Structural Isomers

• Defined as compounds that have the same molecular formula but differ in atom arrangement.

• Example: Butane (C₄H₁₀) has two structural isomers: straight chain and branched chain.

Substituents in Alkanes

• Substituents: Atoms or groups attached to the carbon chain, which include:

  • Alkyl Groups: Groups of carbon atoms attached to carbon chains, using '-yl' ending.

  • Halo Groups: Halogen atoms attached to the carbon chain, denoted as fluoro, chloro, bromo, or iodo in nomenclature.

Table 12.5: Common Substituents

• Displays formulas and names for several common substituents.

Learning Check 2

• IUPAC name for 2-chloro-3-methylpentane involves identifying the longest carbon chain, numbering for substituents, and combining names in proper order.

Solution Steps:

1. Chain Naming: Longest chain has five carbons—Pentane.

2. Numbering: Begin numbering nearest a substituent.

3. Location/Name Prefixation: Describe substituents alphabetically: 2-chloro-3-methylpentane.

Naming Cycloalkanes with Substituents

• One substituent attached leads to prefacing the substituent's name before the cycloalkane name without numbering requirements.

Naming Haloalkanes

• Haloalkanes result from a halogen replacing a hydrogen atom in an alkane.

• They are also named by placing substituents in alphabetical order and numbering based on attachment carbon.

Learning Check 3

• Follow specified steps to draw structural and line-angle formulas for compounds like 3-bromo-1-chlorobutane.

Solution Steps:

1. Identify Carbons: Draw the main chain (Four carbons for butane).

2. Numbering/Placement: Place substituents on indicated carbons based on their positioning.

3. Condensed Formula: Ensure proper hydrogen count to maintain bonding requirements.

Learning Check 4

• The expected responses include:

  • A. 2-chloropentane

  • B. 2,3-dimethylpentane