Alkanes and IUPAC Naming Conventions

Carbon Bonding: Every carbon atom typically forms four bonds.
Rings and Hydrogen Count: For every ring of carbon atoms in a molecule, two hydrogen atoms are removed from the general alkane formula.
Examples in Nature: Cyclohexane, a cyclic alkane, is an odor component found in mangoes.

Single Carbon Molecule: Methane is the simplest alkane, consisting of one carbon atom bonded to four hydrogen atoms.
Bond Lengths:
- Carbon-Carbon (C-C) bond length in ethane is 153 ext{ picometers}.
- Carbon-Hydrogen (C-H) bond length is shorter than C-C because carbon is larger than hydrogen.
Rotation: Carbon atoms in alkanes can rotate freely about sigma bonds, as sigma bonds do not prevent rotation.

Three Carbon Chain: Propane has a continuous chain of three carbon atoms.
Types of Hydrogen Atoms: Propane is the first alkane where different types (positions) of hydrogen atoms exist:
- End Carbons: Hydrogen atoms bonded to the carbons at the ends of the chain are equivalent to each other. There are six such hydrogens.
- Middle Carbon: Hydrogen atoms bonded to the middle carbon are distinct from those on the end carbons. There are two such hydrogens.
Characterizing Carbon Atoms:
- Primary Carbon (1^ extbf{o}): A carbon atom bonded to only one other carbon atom (e.g., the end carbons in propane). Hydrogen atoms attached to primary carbons are called primary hydrogens.
- Secondary Carbon (2^ extbf{o}): A carbon atom bonded to two other carbon atoms (e.g., the middle carbon in propane). Hydrogen atoms attached to secondary carbons are called secondary hydrogens.

Four Carbon Atoms: Butane can be arranged in multiple ways due to isomerism.
Straight Chain (n-alkane): Normal butane (n-butane) is an unbranched chain of four carbon atoms.
Branched Chain: Isobutane (2-methylpropane) is a branched isomer of butane.
Isomers: Butane and 2-methylpropane are constitutional isomers, meaning they have the same molecular formula (C4H{10}) but different structural arrangements.
Boiling Points of Isomers: Isomers have different physical properties:
- n-Butane boiling point: -0.5^ extbf{o}C
- 2-Methylpropane boiling point: -11.7^ extbf{o}C

Methylene Group: A CH_2 group.
Methine Group: A CH group (carbon bonded to one hydrogen and three other carbons).
Methyl Group: A CH_3 group.

Saturated Alkanes (no rings): The general formula is CnH{2n+2}, where n is the number of carbon atoms.
Cycloalkanes (with rings): The general formula is CnH{2n}. For every ring, two hydrogens are removed compared to a straight-chain alkane with the same number of carbons.

Cyclopropane: A three-carbon ring, formula C3H6. This fits the CnH{2n} formula for n=3.
Cyclobutane: A four-carbon ring, formula C4H8. This fits the CnH{2n} formula for n=4.

Historical Origin: Often date back many years and may relate to the molecule's origin.
Example: Formic acid is a common name for methanoic acid; Allium sativum (garlic) gives allicin its common name (the molecule is derived from garlic).
Limitations: Common names can be confusing and do not provide a systematic way to identify structures.

Systematic System: A set of very specific rules where every unique molecule has a unique name, and every name refers to a unique molecule (one-to-one relationship).
Importance: Crucial for scientific communication, ensuring researchers globally refer to the same molecule when publishing or discussing research.
Components of an IUPAC Name:
- Parent Name (Root): Indicates the number of carbon atoms in the longest continuous chain.
- Suffix: Indicates the functional group. For alkanes, the suffix is "-ane."
- Prefixes: Reveal the identity, location, and number of substituents bonded to the longest chain.

Trade Name (Brand Name): Assigned by the manufacturer (e.g., Tamiflu).
Generic Name: The non-proprietary name for a drug (e.g., oseltamivir phosphate for Tamiflu).
IUPAC Name Complexity: IUPAC names for complex pharmaceuticals can be extremely long and intricate (e.g., the full IUPAC name for Tamiflu involves stereochemistry and multiple functional groups). Companies use trade names for marketing and ease of communication.

Identify the Longest Continuous Chain: This chain determines the root name (e.g., hex- for six carbons, oct- for eight carbons).
Not Necessarily Straight: The longest chain may have bends; it is not always drawn as a straight line.
Tie-Breaking Rule (Equal Length Chains): If two chains have the same longest length, select the chain that has more substituents attached to it.

General Rule: Replace '-ane' with '-yl' (e.g., methane becomes methyl, ethane becomes ethyl).
Propyl Groups (3 Carbons):
- Propyl Group (n-propyl): The substituent is bonded through a primary (end) carbon.
- Isopropyl Group: The substituent is bonded through the middle (secondary) carbon.
Butyl Groups (4 Carbons):
- Butyl Group (n-butyl): Attached via an end carbon of a straight four-carbon chain.
- sec-Butyl and isobutyl: These branched butyl groups are complex and do not need to be memorized for this course due to their confusing nature.
- tert-Butyl Group (t-butyl): This group must be known and memorized. It is a common substituent in organic chemistry, characterized by a central carbon bonded to three methyl groups (derived from 2-methylpropane constitutional isomer of butane).

Lowest Possible Numbers: Number the main chain carbons starting from the end that gives the substituent at the first point of difference the lowest possible number.
Example: If numbering from left gives a substituent at carbon \textbf{3} and from right gives one at carbon \textbf{6}, numbering from the left is preferred (\textbf{3} is lower than \textbf{6}).