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Alkanes

Alkanes are a hydrocarbon family that with carbon atoms that are only bonded to each other with single bonds. Alkanes have the general molecular formula, CnH2n+2, where n = number of carbon atoms in the alkane molecule. A normal hydrocarbon alkane is one where all the carbon atoms in the molecule are in a "continuous" chain. A continuous chain does not necessarily mean that the carbons are in a straight line. The carbons can be in a "zig zag" chain as long as the chain is connected by a carbon atom. The simplest alkane is methane, CH4. It is made from one carbon atom bonded to four hydrogen atoms. The table below shows the first ten alkanes.

IUPAC
name
Number of
Carbons
Prefix Molecular
Formula
Structural
Formula
Methane 1 Meth- CH4 CH4
Ethane 2 Eth- C2H6 CH3CH3
Propane 3 Prop- C3H8 CH3CH2CH3
Butane 4 But- C4H10 CH3(CH2)2CH3
Pentane 5 Pent- C5H12 CH3(CH2)3CH3
Hexane 6 Hex- C6H14 CH3(CH2)4CH3
Heptane 7 Hept- C7H16 CH3(CH2)5CH3
Octane 8 Oct- C8H18 CH3(CH2)6CH3
Nonane 9 Non- C9H20 CH3(CH2)7CH3
Decane 10 Dec- C10H22 CH3(CH2)8CH3





Alkyl Groups

An alkyl is basically an alkane minus one of its hydrogen atoms. For example:

        H                    H
        |    remove one H    |
      H-C-H  ============> H-C-  or  CH3-
        |                    |
        H                    H
     methane              methyl
     
        H H                    H H
        | |    remove one H    | |
      H-C-C-H  ============> H-C-C-  or  CH3CH2-
        | |                    | |
        H H                    H H
      ethane                  ethyl
     
     
Alkyl names are used to name branched alkanes. Any branch in an alkane would be named as the number of carbons + "yl".

Rules for naming Alkanes


  1. First, identify the longest continuous chain in the link of carbon atoms, also known as the parent chain. The parent chain does not have to be connected in a straight line, it could be in "zig zag" lines only if it proves to have the most amount of carbon atoms in its chain. Number the carbons in the parent chain starting from the end closest to the branch(es) so that the substituents will have the smallest possible numbers.

  2. Next, find each alkyl branch and assign it a number according to which carbon atom it is attached to. The name for the alkyl branch is followed by "-yl" to indicate the number of carbon atoms are in a branch.

  3. List the substituents (with their carbon number) in alphabetical order followed by the name of the parent alkane. In some cases when there are more than one of a given substituent use the prefixes di-, tri-, tetra-. Prefixes are not used to determine alphabetical order. The structural format should look like this: (number of location)-(branch name)(name of parent chain)

  4. Use commas between numbers and dashes between numbers and words in naming the IUPAC formulas. Do not leave spaces in the name.


Cycloalkanes

Cycloalkanes are alkanes in which a bond is formed between the two terminal carbons in the chain to for a cyclical or ring structure. The prefix cyclo- is written before the name designating the carbon number in the ring (e.g. cyclohexane).

  1. Substituents are named similarly to straight-chained alkanes. The carbons in the ring are numbered so that the substituents have the smallest numbers.

  2. Add the prefix cyclo- to the alkane name

Example:

     
       CH2
      /  \
     CH2-CH2
     
cyclopropane
CH2-CH2 | | CH2-CH2
cyclobutane