Carbon Chemistry

• General Characteristics of Carbon:

  • Carbon is unique due to its ability to form stable covalent bonds with itself and other atoms.
  • Capable of forming long chains or rings, leading to a diverse range of organic compounds.

• Definitions:

  • Biomolecule: A molecule that functions in maintaining and reproducing life.
  • Organic Compounds: A vast majority of carbon compounds; exceptions include oxides of carbon and carbonates.

Molecular Geometry of Carbon

• When carbon is bonded to four atoms, the geometry is tetrahedral.
• VSEPR Model:
  • Valence Shell Electron Pair Repulsion (VSEPR) Model is used to predict the molecular geometry.
  • A double or triple bond is treated as a single bond when determining molecular shapes.

Types of Bonds in Carbon Compounds

• Double Bonds:

  • Involves the sharing of two pairs of electrons between two carbon atoms.
  • Example Representation:
  • $C=C$

• Triple Bonds:

  • Involves the sharing of three pairs of electrons between two carbon atoms.
  • Example Representation:
  • $C riple C$

Hydrocarbons

• Definition: Hydrocarbons are compounds made entirely of carbon and hydrogen.

• Types of Hydrocarbons:

  • Saturated Hydrocarbons: All carbon-carbon bonds are single bonds.
  • Example: Alkanes
  • Unsaturated Hydrocarbons: Contain at least one carbon-carbon double or triple bond.
  • Examples: Alkenes (double bonds), Alkynes (triple bonds).

Alkanes

• Definition: Alkanes are saturated hydrocarbons, consisting only of single carbon bonds.

• Structural Representation:

  • Straight-chain or unbranched hydrocarbons can be represented in their connected form.
  • The actual configuration is not straight but zig-zag because of the tetrahedral arrangement with a bond angle of approximately 109.5 degrees.

• General Formula for Alkanes:

  • The general formula for alkanes is $C_nH_{2n+2}$
  • Example Calculation: an alkane with 8 carbons has:
  • $H = 2(8) + 2 = 18$

• Examples of Straight-chain Alkanes:

  • For 5 Carbons: $C_5H_{12} = CH_3CH_2CH_2CH_2CH_3$
  • For 12 Carbons: $C_{12}H_{26} = CH_3(CH_2)_{10}CH_3$

Structural Isomerism

• Definition: Structural isomerism occurs when two molecules have the same molecular formula (same number of atoms) but different structural arrangements.

• Example: Butane (C4H10) has two structural isomers:

  • n-butane
  • isobutane

• Characteristics of Isomers:

  • Isomers have the same molecular formula but different connectivity of the atoms, leading to variations in chemical properties.

Structural Isomers of Butane (C4H10)

• n-butane: A straight-chain structure.
• isobutane: A branched-chain structure.

Naming Alkanes

• Rules for Naming Alkanes:

  1. Identify the longest continuous chain of carbon atoms (the parent chain).
  2. Number the carbons in the chain starting from the end closest to any branching alkyl group.
  3. Specify the position of any alkyl groups using carbon numbers, and name the alkyl substituents by dropping the "-ane" and adding "-yl".
  • Example: Hexane ($C_6H_{14}$) is represented as: $CH_3(CH_2)_{4}CH_3$
  1. If an alkyl group appears more than once in the structure, use prefixes - di, tri, etc. for multiples and list in alphabetical order irrespective of these prefixes.
  2. For example, $3,4 ext{-dimethylhexane}$ features two methyl groups attached at positions 3 and 4 of the hexane chain.

• Specific Examples of Naming:

  • Neopentane is named as: $2,2 ext{-dimethylpropane}$ based on its branching structure.

Practice Exercises

• Exercises for Naming Alkanes:

  1. Name the following:
  • a) $2,2,4,5 ext{-tetramethylhexane}$
  • b) $3,6 ext{-diethyl-3-methyloctane}$
  1. In-Class Exercise:
  • Write out the normal structure of a hexane (6 carbons) and identify its name as hexane.

• Instructions Before Next Class:

  • Review lecture notes and read from Chapter 20.
  • Complete practice problems from the end of Chapter 20 related to the topics discussed in class.