naming-hydrocarbons

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					  Naming Hydrocarbons
         (nomenclature)




Handout: Hydrocarbons: IUPAC names
    Drawing structures: it’s all good
      2-butene




    This is called the
 “condensed structure” On a test, choose a
    CH3CH=CHCH3        method that shows all Hs
Using brackets can also shorten some formulas:
   CH3(CH2)4CH3 vs. CH3CH2CH2CH2CH2CH3
    Background: formulas for HCs
• Alkanes= CnH2n+2, enes= CnH2n, ynes= CnH2n-2
• Remember enes, then think of what would
  happen if bond was single or triple instead.
• Provides some useful information (e.g. for
  compositional analysis, or to check work)
• Cannot always tell hydrocarbon type based on
  numbers (e.g. propyne vs. propadiene)
Q - how many hydrogens in each of these:
     6 carbon alkane          14
     Alkene: C22H             44
                           8 (2x5 - 2 = 10 - 2)
     Naming: common vs. IUPAC
• Common names used in the 1800’s are still
  used for some compounds today:


                  Acetylene

  Formic acid                     Acetone
• The International Union of Pure and Applied
  Chemistry (IUPAC) was established in 1900s
• Frequent revisions to nomenclature
• Systematic method allows an infinite number
  of compounds to be named given a few rules
     Basic names of hydrocarbons
• Hydrocarbon names are based on: 1) class 2)
  # of C, 3) side chain type and 4) position
• 1) name will end in -ane, -ene, or -yne
• 2) the number of carbons is given by a “Prefix”
  1 meth- 2 eth- 3 prop- 4 but- 5 pent-
  6 hex- 7 hept- 8 oct- 9 non- 10 dec-
• Actually, all end in a, but a is dropped when
  next to a vowel. E.g. a 6 C alkene is hexene
Q - What names would be given to these:
  7C, 9C alkane heptane, nonane
  2C, 4C alkyne ethyne, butyne
  1C, 3C alkene does not exist, propene
Mnemonic for first four prefixes

            First four prefixes
            •   Meth-   Monkeys
            •   Eth-    Eat
            •   Prop-   Peeled
            •   But-    Bananas
         Other prefixes


               • Pent-
  Decade


   ?
 Decimal
               • Oct-
               • Dec-
Decathalon • Hex-, Hept-, Non-
            Numbering carbons
Q- draw pentene                        1-pentene
A- Where’s the bond?
  We number C atoms
• Thus, naming compounds with multiple bonds
  is more complex than previously indicated
• Only if 2+ possibilities exist, are #s needed
• Always give double bond the lowest number
• Q - Name these
                                            C 2H 4
          2-butene
                                           Ethene
                                          3-nonyne
            Multiple multiple bonds
                                     2,3-heptadiene

              2,4,6-nonatriyne
•   Give 1st bond (1st point of difference) lowest #
•   include di, tri, tetra, penta, etc. before ene/yne
•   Comma between #s, hyphen between #-letter
•   You do not need to know ene + yne
                       2-butyne

                            1,2,4-pentatriene
    CH3CH2CH2CH=C=CH2 1,2-hexadiene
              Cyclic structures
• Cyclic structures are circular
• Have “cyclo” in name
• Benzene is not a cyclic structure
                                   • cyclopentane
 Q- Draw these (note: carbons in a double bond
   should be consecutive- 1 and 2, 5 and 6, etc.):
 cyclobutene 1,3-cyclopentadiene cyclopropane
             Naming side chains           CH3

• Names are made up            H3C                 CH3
  of: side chains, root
• 2,3-dimethylpentane                 CH3
• Root is the longest possible HC chain
• Must contain multiple bonds if present
• Add -yl to get name of side chain
• Common side chains include:
  CH3- methyl           CH3CH2- ethyl
  CH3CH2CH2- propyl (CH3)2CH-
• isopropyl
  “iso” (branched) is not an IUPAC convention
• Br- (bromo), Cl- (chloro), F- (fluoro), I- (iodo)
       Naming side chains
Example: use the rules on the bottom of
 handout to name the following structure




Rule 1: choose the correct ending
                             ene
       Naming side chains




Rule 2: longest carbon chain
                               ene
       Naming side chains




Rule 3: attach prefix (according to # of C)
                              ene
                         1-hexene
      Naming side chains




Rule 4: Assign numbers to each carbon
                      1-hexene
      Naming side chains




Rule 4: Assign numbers to each carbon
                      1-hexene
       Naming side chains



    ethyl

                           methyl
                         methyl
Rule 5: Determine name for side chains
                       1-hexene
        Naming side chains



      ethyl

                            methyl
                          methyl
 Rule 6: attach name of branches
                          1-hexene
2-ethyl-4-methyl-4-methyl-1-hexene
         Naming side chains



      ethyl

                                 methyl
                               methyl
 Rule 7: list alphabetically
                          1-hexene
2-ethyl-4-methyl-4-methyl-1-hexene
        Naming side chains



      ethyl

                             methyl
                           methyl
 Rule 8,9: group similar branches
                          1-hexene
2-ethyl-4-methyl-4-methyl-1-hexene
       Naming side chains



    ethyl

                            methyl
                          methyl
Rule 8,9: group similar branches
   2-ethyl-4,4-dimethyl-1-hexene
           Naming side chains
 • Try PE 1 on pg. 1019 (answer to a is wrong)




3-methylhexane
                 4-ethyl-2,3-dimethylheptane




        5-ethyl-2,4,6-trimethyloctane
         Naming side chains
Name the structures below


                  3-ethyl-2-methylpentane




                  3-ethyl-1,5,5-
                   trimethylcyclohexene
                      More practice



4-bromo-7-methyl-2-nonene

2,5-dibromo-6-chloro-1,3-cycloheptadiene



             5-fluoro-7,7-dimethyl-2,4-octadiene
 Pg. 1049 # 24.5, 24.6, 24.7, 24.14, 24.15
             Ignore 24.15 e)
                  Pg. 1049
24.5 - Recall, the exceptions to organic
 compounds are oxides of carbon, carbonates,
 bicarbonates, cyanides.
 b) is an oxide, d) bicarbonate, e) carbonate
24.6 - This is a straight chain molecule as all
 carbons are consecutive.
24.7 - none are possible: a) one too few Hs
 (should be CH3CH2CH3), b) one H too many
 (should be CH2=CHCH2CH3), c) one H too
 many (should be CH3CH=CHCH2CH3).
                      24.15
 2,2-dimethyloctane




1,3-dimethylcyclopentane

               1,1-diethylcyclohexane



        6-ethyl-5-isopropyl-7-methyl-1-octene
   Aromatic nomenclature
There are 2 naming methods
1) Numbering carbons
2) ortho, meta, para (stomp) 1,2-dimethylbenzene
                             orthodimethylbenzene

ST Ortho       Meta

                           1,3-dimethylbenzene
                    Para   metadimethylbenzene

  Benzene is very stable
   (does not generally     1,4-dimethylbenzene
    undergo addition)      paradimethylbenzene
              More practice
• Build a molecule that can be named
  according to the rules that we have talked
  about. Make it challenging.
• Place your model at a vacant lab station.
• On a scrap piece of paper write the following:
  1) your station number, 2) the structure of
  your molecule, 3) the name of the structure.
  Give this to your teacher.
• Rotate through the stations, drawing the
  structures and determining their names. At
  the end of the class students will reveal the
  answer with an explanation.             For more lessons, visit
                                          www.chalkbored.com

				
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posted:11/24/2011
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