Study Notes on Organic Chemistry: Alkanes and Halogenated Hydrocarbons

Chapter 12 Organic Chemistry: Alkanes and Halogenated Hydrocarbons

Definition: Organic chemistry is defined as the study of the chemistry of carbon compounds.
Significance of Carbon:
- Carbon is unique due to its unprecedented chemical diversity.
- The diversity arises from several key properties of carbon atoms:
- Carbon atoms bond strongly to other carbon atoms.
- Carbon atoms bond strongly to various other chemical elements.
- Carbon atoms can make a large number of covalent bonds (four per atom).
- Carbon atoms can participate in single, double, and triple bonding.

Characteristics of Alkanes:
- Alkanes are hydrocarbons that consist exclusively of single-bonded carbon and hydrogen atoms.
- Type: Referred to as saturated hydrocarbons, indicating the presence of only single bonds.
- Each carbon atom, while bonding with other carbon atoms, is also attached to the maximum number of hydrogen atoms.
General Formula:
- The general formula for alkanes is given as:
  CnH{2n+2}
- This formula allows the derivation of molecular formulas for any alkane given a specific number of carbon atoms.

Definition of Isomers: Isomers are compounds that share the same molecular formula but exhibit different structural formulas and properties.
Example:
- Butane (C4H10) possesses two isomers:
- Normal Butane (n-butane)
- Isobutane
- Although both isomers share the molecular formula C4H10, the arrangement of atoms/groups differs, leading to varying properties.
Branched-Chain Alkanes:
- Alkanes with carbon atoms not connected in a single continuous chain are categorized as branched-chain alkanes.
Structural Isomers:
- Structural isomers have the same molecular formula but differ in atom connectivity.
Conformational Isomers:
- Molecules with the same connectivity but different spatial arrangements of the same compound are termed conformational isomers or conformers.

Molecular Formula:
- Displays the number of each type of atom present in the molecule.
Condensed Formula:
- Shows all atoms in a molecule using as few bonds as possible.
Lewis Structure:
- Offers complete connectivity, encompassing all atoms and all bonds, often termed as expanded structural formula.

Substituents and Naming:
- The IUPAC naming convention for organic compounds comprises three fundamental parts:
- Substituents (attachments)
- Parent Name (number of carbons in the longest continuous chain)
- Suffix (family name)
Basic Rules for Naming Alkanes:
1. Identify and name alkanes according to the longest continuous chain (LCC) of carbon atoms, determining the base name by adding the suffix -ane.
2. For branched hydrocarbons, assign numbers to the carbon atoms of the LCC in a way that provides the lowest numbers to the carbon atoms carrying substituents.
- Hyphens separate numbers from names; commas separate numbers.
1. Arrange the substituent names alphabetically prior to the parent compound’s name.
- Repeat numbers for identical groups on the same carbon atom, using Greek prefixes (di-, tri-, tetra-), though these prefixes are not considered in the alphabetical listing of substituents.

Nature of Alkanes:
- As nonpolar compounds, alkanes are characterized by similar electronegativities of carbon and hydrogen, leading to equal sharing of electrons in covalent bonds.
- Consequently, all alkanes are nonpolar, irrespective of their geometric shape.
Implications in Aqueous Solutions:
- Alkanes do not mix well with polar substances like water; they are solubilized effectively in non-polar solvents.
Density Comparison:
- Most alkanes have densities lower than water (< 1.0 gram/mL), causing them to float rather than sink (as observed in crude oil spills).

Reactivity Profile:
- Generally, alkanes are not considered highly reactive molecules.
- They can undergo combustion reactions with oxygen, proving to be excellent fuel sources.
- Complete Combustion: Produces carbon dioxide and water.
- Incomplete Combustion: Results in carbon monoxide and water, the latter being hazardous.
Reactions with Halogens:
- Alkanes react with halogens, resulting in the formation of halogenated hydrocarbons.

Haloalkanes:
- Halogens often serve as substituents on alkane chains, referred to as alkyl halides.
- Substituent Nomenclature: The names of the substituents include: fluoro, chloro, bromo, and iodo.
- Reactivity Hierarchy: Fluorine is the most reactive halogen; iodine is the least reactive.
Naming Protocol:
- The naming conventions for haloalkanes are consistent with those for branched-chain alkanes, with halogens recognized as substituents.
Notable Haloalkanes:
- Examples include chloroform and certain anesthetics such as ethyl chloride and Halothane.

Definition:
- Cycloalkanes are characterized as ring-shaped alkanes.
Naming Convention:
- The nomenclature involves adding the prefix cyclo to the alkane name corresponding to the number of carbon atoms within the ring structure.
Common Cycloalkanes:
- The most prevalent ring structures found in nature typically consist of five or six carbon atoms.

Cyclopropane
- Molecular Formula: C3H6
- Components: Ball-and-stick models, skeletal structure
Cyclobutane
- Molecular Formula: C4H8
Cyclopentane
- Molecular Formula: C5H10
Cyclohexane
- Molecular Formula: C6H12