Nomenclature for organic chem by Studymaster


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									 Organic Nomenclature
The naming of molecules
 Suitable for Year 12 Chemistry
      Made by Richard Henty
The first thing you need to memorise, is the prefix
given to molecules with a certain number of carbons
in a straight chain.
      1 = Meth-            2 = Eth-
      3 = Prop-            4 = But-
      5 = Pent-            6 = Hex-
      7 = Hept-            8 = Oct-
      9 = Non-             10 = Dec-
You will see these prefixes come up in molecules like
methane, ethanol, propyl butanoate, cyclohexene.
Notice that the ending (suffix) changes.
    Alkanes. The simplest molecules, particularly if they
    are straight chained.
    For these, count the number of linked carbons, find
    the prefix and put -ane (the suffix) after it.
            H           H       H       H
                                                4 carbons, but- & -ane = butane
    H       C C C C                         H                    H
            H           H       H       H                                3 carbons
                                                             H   C   H
H   C           H
                        8 carbons = octane
                                                             H   C   H

H   C           H
                    H       H       H       H     H
                                                             H   C   H

H   C C C C C C                                       H   Even though it is “bent”, it
                H           H       H       H     H       is called a straight chain.
How many carbon atoms are there in the longest carbon chain?
                                              There are fourteen
                                              carbon atoms in the
                                              longest chain. It
          H   C   H
                                              does not matter that
                                              it looks bent.
          H   C   H
                      H   H       H   H   H

          H   C C C C C C                       H

                  H            H      H   H
                  C   H       H

                      H       H
                                  H   H   H      H   H    H

          H   C C C C C C C C C                               H

              H   H       H   H       H   H     H    H    H
    Alkanes that have extra carbons and hydrogens sticking
    off of them are called branched alkanes. The size of the
    branch will affect its name.
                  This molecule has two branches, one with three
H    C   H        carbons and one with two carbons. The other
                  fourteen carbons make up the alkane “backbone”.
H    C   H
             H     H       H   H   H

H    C C C C C C                       H

          H             H      H   H
         C    H        H

        C H
              H        H
                           H   H   H   H   H   H

H   C C C C C C C C C                              H

     H    H        H    H      H   H   H   H   H
            H                H       H       H    H    H    H       H   H

      C H       H        H   C C C C C C C C                                 H

                             H              H          H            H   H
    H C H       H              C H C   C   H H        H H       H

H   C C         H
                 H   H   H
                                   C   C      H       H H       H
        H   C C C C              H            H   C   H

                 H   H   H
            C   H
                H    H

                                         A branch that has one carbon
            C C C        H                in it is called a methyl group.
                H    H
                                         A branch that has two carbons
        H   C   H
                                           in it is called an ethyl group.
        H   C   H                    A branch that has three carbons
                                         in it is called a propyl group.
The branch name is added at the start of the alkane
name, like another prefix. Numbering my be used.
For example:
                    These contain a single branch where
                    only one position is possible.
                     These contain one branch, but there
                     are two possible positions, so we
                     must show what carbon it is on.
2,2-dimethylbutane         These contain multiples of the same
2,3,4-trimethylhexane      branch, so we must number them
3,3,4,4-tetramethylheptane and use another prefix as well.

2-methyl-3-ethylheptane    Two different branches, with
                           their positions numbered
When numbering, you can count from either end of the
the longest straight chain. But, the branch number
must be the lowest possible.

 The longest chain in this molecule is five carbons,
 with a 1 carbon methyl branch.
 If we count from the left, the methyl group is on
 carbon #4.
 If we count from the right, the methyl group is on
 carbon #2. This is the preferred number.
 This is 2-methylpentane
If there are two branches, the sum of their numbers
must be the lowest.

The longest chain is again five, hence pentane.
Two methyl branches.
From the left, on carbons #3 and #4.
From the right, on carbons #2 and #3. This is the
preferred numbering.
This molecule is 2,3-dimethylpentane
What are the names of these molecules?


                           The same no matter
                           which way you count.

                    No number needed (but OK if you put 2)
                    because the only place for a methyl on
                    butane is at carbon #2.
What is the name for this big molecule?

      H       H    H    H    H    H       H   H

  H   C C C C C C C C                             H

      H            H         H            H   H
        C H C   C H H       H H       H

            C   C   H       H H       H

                    H   C   H


It does not matter what order you put the branches, so long as
they have the correct numbering, and dashes between them.
Functional groups.
Alkanes are the only molecules that do not have a
functional group.
A functional group is a distinct part of a molecule that is
involved in a chemical reaction and gives the molecule its
physical characteristics.
Different functional groups result in different chemical and
physical properties.
You will need to be able to identify a functional group
when you find it in a molecule. Most molecules have only
one functional group. Some have two of the same, some
have two different or more.
Functional groups alter the name of the straight chain of carbons
that they are found upon.
Most change the suffix -ane to something else.
If there is a double bond then it is now -ene (Alkene family)
If there is a triple bond then it is now -yne (Alkyne family)
If there is an -OH attached then it is now -anol (Alcohol family)
If there is a -COOH at one end then it is now -anoic acid
(Carboxylic acid family)
If there is a halogen atom attached then it is still -ane, but given
a prefix of chloro (if its chlorine) or bromo.
Some molecules: propene, ethyne, methanol, chloroethane,
butanoic acid, 2-pentene, 2-methyl-2-propanol,
2,3-dibromobutane, 3-pentyne.
Alkenes (easily identified by the double bond).
In the same way as if there were a branch, the alkene is
numbered so that the double bond starts at the lowest
numbered carbon possible.
                 Two carbons = ethene (only one place the
                 double bond can go, so no number)

                 Three carbons = propene (only one place
                 the double bond can go, so no number).

Butene is the first alkene where there are two possible
places for the double bond.
On the left 1-butene and on the right 2-butene.
Some text books give a different way of writing the
number into the name.
2-butene may be seen as but-2-ene. The reason for this
is that the number is right next to the functional group it
is counting for.
Either way is acceptable, because if you drew 2-butene
or but-2-ene you would get the same thing. There is no
The only time confusion occurs is if there are two
different functional groups in the same molecule. (Rare
in Year 12 or 13 Chemistry).
You decide which you prefer using; here we will use the
2-butene method.
Name these alkene molecules. A branch can be treated
in the same way as with alkanes.



Alkene molecules can have the same atoms, but
rearranged slightly differently about the double bond. This
is because the double bond cannot rotate. These are
geometric isomers, given cis - or trans- notation.

  Trans-2-pentene               Cis-2-pentene
  The main branch               The main branch
  continues on opposite         continues on the same
  sides of the double bond.     side of the double bond.
What are the names of these molecules, and what are their
cis or trans name if needed.



 trans-2-pentene                ethene
Alcohols can have the -OH group positioned on any of the
carbons within the chain. The -OH group must be numbered
with the lowest number.

 1-butanol                    2-methyl-1-butanol

2-pentanol                   3-ethyl-3-pentanol

2-methyl-2-propanol                 methanol
Using the name 2-propanol is that same as using the name
propan-2-ol. Both yeild the same structure.
Either is appropriate.
The 2-propanol method will be used here.
Alcohols - Primary, secondary, tertiary strucutres.
The position of the -OH with the structure classifies it as 1o,
2o, an 3o.
If the C-OH is bonded to one
other carbon it is primary, 1o.

If the C-OH is bonded to two
other carbons (one either side)
then it is secondary, 2o.

If the C-OH has three other
carbons bonded to that carbon
then it is tertiary, 3o.
Carboxylic acids always have their functional group at the
end of the chain on carbon one.
Count the number of carbons, use the prefix and then
anoic acid.

 Butanoic acid                2-methylbutanoic acid

 Methanoic acid

                             3-methylbutanoic acid
Propanoic acid
Haloalkanes - these are molecules that contain one or
more halogen atom - F, Cl, Br or I.
The molecule is considered to be an alkane derivative
containing a halogen, so the longest carbon chain alkane is
identified, and the halogen is numbered based on its
F prefix is fluoro, Cl is chloro, Br is bromo, I is iodo

1-bromobutane                      2-chlorobutane

1-chloropropane                    2-methyl-2-chlorobutane
Aldehydes and ketones
Both of these contain a C=O (carbonyl group), but its position
is significant.
For an aldehyde, the C=O must
be on the first or last carbon
(always counted as carbon #1).
For a ketone, the C=O must be
within the carbon chain and
not on the first or last carbon.
Aldehydes have the suffix -al.
Ketones have the suffix -one.

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