Alkanes and IUPAC Nomenclature

Unit 3: Organic Chemistry - Alkanes

IUPAC Nomenclature

  • IUPAC stands for The International Union of Pure and Applied Chemistry.

  • It is an international federation of National Adhering Organizations representing chemists in different countries.

  • IUPAC is a member of the International Council for Science (ICSU).

  • IUPAC is registered in Zürich, Switzerland.

  • The administrative office, known as the "IUPAC Secretariat", is located in Research Triangle Park, North Carolina, United States.

Hydrocarbons

  • Hydrocarbons are compounds made up of carbon and hydrogen atoms ONLY.

Naming Hydrocarbons

  • Prefixes for the number of carbons:

    • 1 = meth-

    • 2 = eth-

    • 3 = prop-

    • 4 = but-

    • 5 = pent-

    • 6 = hex-

    • 7 = hept-

    • 8 = oct-

    • 9 = non-

    • 10 = dec-

  • Suffixes for the number of C-C bonds:

    • None = -ane

    • 2 = -en-

    • 3 = -yn-

  • Suffixes for functional groups:

    • Alcohol = -ol

    • Carboxylic Acid = -ic acid

Homologous Series

  • All members of a homologous series have:

    • The same general formula

    • The same functional group

    • Similar chemical properties

    • Gradation in their physical properties, such as melting and boiling point

  • Examples of homologous series:

    • Alkane (-ane)

    • Alkene (-ene)

    • Alkyne (-yne)

    • Alcohol (-ol)

    • Alkyl Halide (Fluoro, chloro, bromo and iodo)

    • Carboxylic acid (-ic acid)

    • Aromatic

    • Ester (-yl -oate)

Alkanes

  • Alkanes are the simplest family of hydrocarbons, containing only carbon and hydrogen.

  • Alkanes contain only carbon-hydrogen bonds and carbon-carbon single bonds.

  • Types of alkanes:

    • Linear (straight) alkane

    • Branched alkane

    • Cyclic alkane

  • They are only bonded to hydrogens.

  • Saturated: No double/triple bonds

  • General formula: CnH{2n+2}

  • Aliphatic family of organic compounds.

Aliphatic

  • Belongs to the aliphatic family of organic compounds

  • General formula for cyclic alkanes: CnH{2n}

Saturated Hydrocarbon

  • Hydrocarbons containing only single bonds.

Sigma (σ) Bonds

  • Each single bond is made up of 2 electrons, called a sigma (σ) bond.

  • There are 4 equal sigma (σ) bonds.

  • 1 pair of electrons comes from the s shell.

  • 3 pairs of electrons come from the p shell.

  • They hybridize to form 4 sp^3 hybrid orbitals.

  • Bond angle: 109.5º

Properties of Alkanes

# of C

Name of Alkane

Chemical Formula

B.P. (°C)

State at SATP

Solubility

1

methane

CH_4

-162

Gas

-

2

ethane

C2H6

-89

Gas

-

3

propane

C3H8

-42

Gas

-

4

butane

C4H{10}

-1

Gas

-

5

pentane

C5H{12}

36

Liquid

immiscible

6

hexane

C6H{14}

68

Liquid

immiscible

7

heptane

C7H{16}

98

Liquid

immiscible

8

octane

C8H{18}

126

Liquid

immiscible

9

nonane

C9H{20}

151

Liquid

immiscible

  • Boiling point increases with increasing # of C’s: Gas → liquid → solid

  • Addition of C and 2H increases boiling point

Uses of Alkanes

  • Primarily as fuels.

  • Derivatives can be found in paints, plastics, cosmetics, cleaners, and pharmaceuticals.

Naming Straight Chained Alkanes

  1. Look for double/triple bonds or benzene rings.

  2. Choose the cyclic chain or the longest, most substituted carbon chain to be the parent chain.

  3. Count the longest chain of carbons.

  4. prefix + “ane” (suffix)

  5. If your hydrocarbon doesn’t have any double/triple bonds or benzene rings, it is an alkane.

Naming Branched Alkanes

  1. Choose the cyclic chain or the longest, most substituted carbon chain to be the parent chain.

  2. Count the longest chain of carbons.

  3. A carbon bonded to a branch must have the lowest possible carbon number. If there are no functional groups, then any branch present must have the lowest possible number.

  4. Branches are named by the number of C’s and end in -yl.

  5. Take the alphabetical order into consideration; that is, after applying the two rules given above, make sure that your branches are written in alphabetical order.

  6. prefix + “ane” (suffix)

  7. If your hydrocarbon doesn’t have any double/triple bonds or benzene rings it is an alkane.

Naming Cyclic Alkanes (Cycloalkanes)

  1. Look for double/triple bonds or benzene rings

  2. Longest cyclic chain of carbons becomes parent chain.

  3. A carbon bonded to a branch must have the lowest possible carbon number. If there are no functional groups, then any branch present must have the lowest possible number.

  4. Branches are named by the number of C’s and end in -yl.

  5. Take the alphabetical order into consideration; that is, after applying the two rules given above, make sure that your branches are written in alphabetical order.

  6. cyclo + prefix + “ane” (suffix)

  • Use the ring structure as the “parent” name

  • C-C Bonds “cyclo”+ prefix + ane

  • They belong to the aliphatic family of organic compounds

  • If there are branches, number the carbons in the ring so the branches get the lowest possible number sequence