Chemistry Chapter 22

1
Chemistry Chapter 22

• Hydrocarbons

2
Organic Chemistry

• Compounds that contain carbon are called organic
  compounds because they are produced by living
  organisms.
• Not all compounds that contain carbon are
  classified as organic.
• Carbon oxides, carbides and carbonates are
  considered inorganic compounds.
• Organic chemistry is totally devoted to the study
  of carbon containing compounds.

3
Hydrocarbons

• The simplest organic compounds are the
  hydrocarbons, which contain only the elements
  hydrogen and carbon.
• Thousands of different hydrocarbons are known of
  at this time.
• The reason that there are so many different
  hydrocarbons is the fact that hydrogen with its
  single valence electron is so abundant that it is
  very easy for the four valence electrons of
  carbon to grab.

4
Hydrocarbons

• Since carbon forms four bonds and hydrogen can
  only form one bond, the simplest hydrocarbon is
  CH4.
• CH4 is called methane and is an excellent fuel
  and main component of natural gas

5
Straight Chain Alkanes

• Alkanes are hydrocarbons that have only single
  bonds between atoms.
• Methane (CH4) is the smallest member of alkanes.
• The next member is ethane (C2H6)
• Followed by propane (C3H8)
• Butane (C4H10) is next.

6
Straight Chain Alkanes

• The alkanes all end in ane.
• The alkanes with five or more carbons in a chain
  have names that use a prefix derived from the
  Greek or Latin word for the number of carbons in
  each chain.
• For example pentane has 5 carbons and octane has
  8 carbons.
• The reason the first four alkanes in the series
  do not have a prefix is because they were named
  prior to their structure being known.

7
Straight Chain Alkanes

• A series of compounds that differ from one
  another by a repeating unit is called a
  homologous series.
• A homologous series has a fixed numerical
  relationship among the numbers of atoms.
• For alkanes, the relationship between the numbers
  of carbon and hydrogen atoms can be expressed as
  CnH2n2 , where n is equal to the number of
  carbon atoms in the alkane.

8
Naming Branched Chain Alkanes

• For the purpose of naming, branched chain alkanes
  are viewed as consisting of a straight chain of
  carbon atoms with other carbon atoms or groups of
  carbon atoms branching off the straight chain.
• The longest continuous chain of carbon atoms is
  called the parent chain.
• All side branches are called substituent groups.
• This is because they appear to substitute for a
  hydrogen atom in the straight chain.

9
Naming Branched Chain Alkanes

• The International Union of Pure and Applied
  Chemistry (IUPAC) rules for naming organic
  substances.
• Count the number of carbon atoms in the longest
  continuous chain. Use the name of the straight
  chain alkane with that number of carbons as the
  name of the parent chain of the structure.
• Number each carbon in the parent chain. Locate
  the end carbon closest to a substituent group.
  Label that carbon position one. This step gives
  all the substituent groups the lowest position
  numbers possible.

10
Naming Branched Chain Alkanes

• Name each alkyl group substituent. The names of
  these groups are placed before the name of the
  parent chain. (page 702 has common alkyl group
  names)
• If the same alkyl group occurs more than once as
  a branch on the parent structure, use a prefix
  such as (di, tri, tetra, ect.) Then use the
  number of the carbon to which each is attached to
  indicate its position.
• Whenever different alkyl groups are attached to
  the same parent structure, place their names in
  alphabetical order. Do not consider the prefixes
  (di, tri, ect.) when determining alphabetical
  order.

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Naming Branched Chain Alkanes

• Write the entire name using hyphens to separate
  numbers from words and commas to separate
  numbers.

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NUMBERING BRANCHED CHAINSThis is an isobutane
molecule

• A. CH3
• ?
• CH3CHCH3
• 1 2 3

• B. CH3
• ?
• CH3CHCH3
• 3 2 1

• C. 1CH3
• ?
• CH3CHCH3
• 2 3

• D 1CH3
• ?
• CH3CHCH3
• 3 2

13
Naming Branched Chain Alkanes

• The longest chain in the structures in the
  previous slide contained 3 carbons.
• Therefore the name of the parent chain will be
  propane.
• No matter wherever the numbering starts in this
  molecule the alkyl group is at position 2.
• The alkyl group here is a methyl group because it
  has only one carbon.
• No prefix is needed because only one alkyl group
  is present
• alphabetical order does not needed to be
  considered because only one group is present.

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Naming Branched Chain Alkanes

• After applying the rules, you can write the IUPAC
  name 2-methylpropane for isobutane.
• CH3 ? substituent group methyl group at
• ? position 2
• CH3CHCH3 ? 3 carbon parent chain propane

15
Name These Compounds

• C C C C
• ? ? ?
• C C C C C C
• ?
• C C C C
• C C C
• ?
• C C C C C C C C C C
• ?
• C

16
Cyclic Alkanes

• An organic compound that contains a hydrocarbon
  ring is called a cyclic hydrocarbon
• To indicate that a hydrocarbon has a ring
  structure, the prefix cyclo -, is used with the
  hydrocarbon name.
• Cyclic hydrocarbons that only contain single
  bonds are called cycloalkanes.

17
Naming Substituted Cycloalkanes

• Cycloalkanes are named by following the same
  IUPAC rules used for straight chain alkanes, with
  a few modifications.
• With cycloalkanes, the ring is considered to be
  the parent chain.
• Since a cyclic structure has no ends, numbering
  is started on the carbon that is bonded to the
  substituent group.
• When there are two or more substituents, the
  carbons are numbered around the ring in a way
  that gives the lowest possible set of numbers for
  the substituents.

18
Properties of Alkanes

• Alkanes are nonpolar compounds that have lower
  melting and boiling points than polar molecules
  of similar size and mass.
• Since alkanes are non polar, they will not be
  soluble in a polar substance such as water.
• Remember, Like dissolves Like.

19
Multiple Carbon Bonds

• Carbon atoms can bond to one another not only by
  single covalent bonds but, also double and triple
  covalent bonds.
• A hydrocarbon in which there are only single
  covalent bonds is called a saturated hydrocarbon.
  
• A hydrocarbon that contains at least one double
  or triple bond is called an unsaturated
  hydrocarbon.

20
Alkenes

• Unsaturated hydrocarbons that contain one or more
  double covalent bonds between carbon atoms in a
  chain are called alkenes.
• The general formula for an alkene is CnH2n.

21
Naming Alkenes

• Alkenes are named in much the same way as
  alkanes.
• Their names are formed by changing the ane
  ending of the corresponding alkane to ene.
• It is important to specify the location of the
  double bond.
• So you just number the parent chain and label the
  double bond with the corresponding number.

22
Naming Branched Chain Alkenes

• When naming branched chain alkenes, follow the
  IUPAC rules for naming branched chain alkanes
  with two differences.
• First in alkenes the parent chain is always the
  longest chain that contains the double bond,
  whether it is the longest chain of carbon atoms
  or not.
• Second, the position of the double bond, not the
  branches determines how the chain is numbered.
• Look at the example problem on page 713

23
Alkynes

• Unsaturated hydrocarbons that contain one or more
  triple bonds between carbon atoms in a chain are
  called alkynes.
• The simplest and most commonly used alkyne is
  ethyne, which is know as acetylene.

24
Naming Alkynes

• Straight chain alkynes and branched chain alkynes
  are named in the same way as the alkenes.
• The only difference is that the name of the
  parent chain ends in yne rather than ene.

25
Properties of Alkynes

• Alkynes have physical and chemical properties
  similar to those of alkenes.
• Alkynes are generally more reactive than alkenes.

26
Isomers

• Isomers are two or more compounds that have the
  same molecular formula, but different molecular
  structures.
• There are two main classes of isomers.
• Structural isomers are bonded in different
  orders.
• These have different chemical and physical
  properties despite having the same formula.
• Stereoisomers are isomers in which all atoms are
  bonded in the same order but are arranged
  differently in space.

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Stereoisomers continued

• Geometric isomers are a category of
  stereoisomers, that result from different
  arrangements of groups about carbon atoms that
  are double bonded to each other.
• Optical isomers are a category of stereoisomers
  that result from the two possible arrangements of
  four different atoms or groups of atoms bonded to
  the same carbon atom.
• The two isomers are chiral because they are a
  mirror image of each other.

28
Aromatic Hydrocarbons

• Organic compounds that contain a benzene rings as
  a part of their structure.
• These are called aromatic because of the pleasant
  aromas that were found in some plant oils that
  contained the benzene ring structure.
• Aromatic hydrocarbons tend to be less reactive
  than alkenes or alkynes because they have no
  double bonds.
• Instead, electrons are shared evenly over the
  entire benzene ring.

29
Petroleum

• The major sources of hydrocarbons are petroleum
  and natural gas.
• Petroleum can be separated into components of
  different boiling ranges by the process of
  fractional distillation.