Chem 150 Unit 2 - Hydrocarbons

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Chem 150Unit 2 - Hydrocarbons Functional Groups

• Organic chemistry is the chemistry of carbon. The
  name organic reflect the fact that organic
  molecules are derived from living organisms. In
  this unit will start by looking at four families
  of organic molecules that are grouped together as
  the hydrocarbons. We will also look at some
  functional groups that define some of the other
  families of organic molecules.

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Organic Chemistry

• Organic chemistry is the chemistry of carbon.
• There are three forms of pure carbon
• Diamond
• Graphite

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Organic Chemistry

• Organic chemistry is the chemistry of carbon.
• There are three forms of pure carbon
• BuckminsterfullereneBucky Balls

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Hydrocarbons

• Organic molecules contain carbon combined with
  other elements.
• Organic molecules are grouped into families
• Members of a family share common structural,
  physical, and chemical characteristics.
• There are four families that contain molecules
  made of only carbon and hydrogen.
• Hydrocarbons
• Alkanes
• Alkenes
• Alkynes
• Aromatics

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Hydrocarbons
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Alkanes

• Alkanes are hydrocarbons that contain only
  carbon-carbon single bonds.
• Every carbon atom participates in 4 single bonds,
  either to another carbon or to a hydrogen.
• Every hydrogen atom is bonded to a carbon by a
  single bond.

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Alkanes

• Alkanes are hydrocarbons that contain only
  carbon-carbon single bonds.

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Alkanes

• Alkanes in which the carbons are connected in a
  straight chain are called normal alkanes.
• Alkanes that are branched are called branched
  chain alkanes.

n-hexane
2-methyl-pentane
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Alkanes

• For a discusion on the structure of alkanes,see
  the Unit 2Elaboration - Alkane Structure

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Alkanes

• Alkanes, along with the other hydrocarbons, are
  non-polar.
• They interact with each other only through London
  dispersion forces.
• This is why they have relatively low boiling and
  melting points.

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Alkanes

• They interact with each other only through London
  dispersion forces.
• Note how the boiling points increase with
  molecular weight.

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Molecule in the News
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Molecule in the NewsMelamine
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Organic Molecules in the News!!

• http//www.cbc.ca/health/story/2007/09/06/additive
  s-lancet.html?refrss
• http//www.medpagetoday.com/Psychiatry/ADHD-ADD/tb
  /6610

Quinoline yellow
Sodium benzoate
Carmoisine
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Alkanes

• Alkanes, cannot be named based on their molecular
  formulas
• For example, all of the molecules shown below
  share the same molecular formula,
  C6H14(hexacarbon tetradecahydride?)

n-hexane
2-methyl-pentane
3-methyl-pentane
2,2-dimethylbutane
2,3-dimethylbutane
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Alkanes

• Organic chemists use a systematic set of rules,
  called the IUPAC rules, to name organic molecules
  based on their structural formulas instead of
  their chemical formulas.

n-hexane
2-methyl-pentane
3-methyl-pentane
2,2-dimethylbutane
2,3-dimethylbutane
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Alkanes

• For a discussion on naming alkanes,see the Unit
  2Elaboration - Naming Alkanes

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Constitutional Isomers

• When two or more molecules share the same
  molecular formula, but have different atomic
  connections, they are called constitutional
  isomers.

n-hexane
2-methyl-pentane
3-methyl-pentane
2,2-dimethylbutane
2,3-dimethylbutane
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Conformations

• Carbon-carbon single bonds are free to rotate
• This leads to different shapes for some molecules
• These should not be confused with isomers.

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Conformations

• All of the 3-dimensional models shown below are
  for the n-butane.
• They were generated by rotating the central
  carbon-carbon bond.
• They all share the same structural formula.

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Conformations

• All of the 3-dimensional models shown below are
  for the n-butane.
• They were generated by rotating the central
  carbon-carbon bond.

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Conformations

• Switching from one conformation to another does
  not require the breaking and making of covalent
  bonds.
• Switching from one isomer to another does require
  the breaking and making of covalent bonds.

n-butane
2-methylpropane
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Conformations

• For a discussion on conformations,see the Unit
  2Elaboration - Conformations

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Cycloalkanes

• When there are three or more carbons in a
  straight chain, the ends can be joined to make
  rings.
• In naming these molecules, the prefix cyclo- is
  used to indicate the ring
• Skeletal structural formulas are used to
  represent the rings in structural formulas

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Cycloalkanes

• In naming these molecules, the prefix cyclo- is
  used to indicate the ring

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Cycloalkanes

• The carbon-carbon single bonds for the carbons in
  a ring are no longer free to rotate.
• This leads to a new type of isomer
• Since the two structures share the same name,
  they are not constitutional isomers.

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Cycloalkanes

• Isomers which share the same atomic connections,
  and therefore, the same IUPAC name are called
  stereoisomers.
• When this occurs due to restricted rotation about
  a covalent bond, they are called geometric
  isomers
• The prefix cis- and trans- are used to
  distinguish geometric isomers.

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Questions

• Draw the condensed structural formulas for the
  following molecules
• 1-ethyl-2-methylcyclopentane
• 1,1-dimethylcyclobutane
• 1,1-dimethyl-2-propylcyclopropane
• Do any of these molecules have cis- and trans-
  geometric isomers?

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Alkenes, Alkynes Aromatic Compounds

• The remaining three families of hydrocarbons are
  unsaturated.
• Alkanes are saturated, which means they contain
  the maximum number of hydrogens per carbon.
• For alkanes CnH(2n2)
• Alkenes, Alkynes and Aromatics are unsaturated,
  which means they contain less than the maximum
  number of hydrogens per carbon.
• Structurally, this means that they have
  carbon-carbon double or triple bonds

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Alkenes, Alkynes Aromatic Compounds

• Alkenes are hydrocarbons that contain at least 1
  carbon-carbon double bond.
• Examples

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Alkenes, Alkynes Aromatic Compounds

• Alkynes are hydrocarbons that contain at least 1
  carbon-carbon triple bond.
• Examples

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Alkenes, Alkynes Aromatic Compounds

• Aromatics are unsaturated ring molecules
• They are often drawn to look like alkenes, but
  they behave much differently than alkenes.
• They have an alternating pattern of double and
  single bonds within a ring.
• Benzene is an example

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Alkenes, Alkynes Aromatic Compounds

• The physical properties of all hydrocarbons are
  the same
• The have essentially one noncovalent interaction,
  which isthe London dispersion force.
• They have no electronegative atoms and therefore
  have
• No ion/ion interactions
• No dipole/dipole interactions
• No hydrogenbonding interactions

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Alkenes, Alkynes Aromatic Compounds

• Naming of Alkenes and Alkynes work the same as
  for alkanes, with these added rules
• The parent chain must include both carbons in all
  double and triple bonds.
• Pick the longest chain that also contains all
  double and triple bonds
• The -ene ending is used of alkenes
• The -yne ending is used for alkynes.
• The number of the first carbon in the double or
  triple bond is included in the name to locate the
  double or triple bond.
• Number the parent chain from the end that is
  closes to the first double or triple bond.

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Alkenes, Alkynes Aromatic Compounds

• Naming of Aromatics is based on benzene
• When the molecule is build on benzene, the parent
  name is benzene.
• There are also many common names used to describe
  aromatic compounds.

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Alkenes, Alkynes Aromatic Compounds

• Naming of Aromatics is based on benzene
• Aromatic compounds can contain multiple aromatic
  rings

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Alkenes, Alkynes Aromatic Compounds

• Benzo(a)pyrene found in tobacco smoke is
  converted to carcinogenic products in the liver
  (see below) which link to DNA and cause mutations.

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Practice Quiz 1 KEY

• http//www.chem.uwec.edu/Chem150_S07/course/answer
  s/C150-Quiz-1-key.swf

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Alkenes, Alkynes Aromatic Compounds

• There are many aromatic molecules found in
  biology
• Some aromatic compounds contain nitrogen and
  oxygen atoms
• For example, the nucleotide base Adenine, which
  is used to make DNA and RNA

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Alkenes, Alkynes Aromatic Compounds

• Like cycloalkanes, some alkenes can have cis and
  trans isomers
• This is due to restricted rotation about the
  double-bond.
• Not all double bonds produce cis and trans
  isomers
• Each carbon participating in the double bond must
  have two different substituents attached to them

A ? B AND X ? Y
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Alkenes, Alkynes Aromatic Compounds

• Like cycloalkanes, some alkenes can have cis and
  trans isomers

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Alcohols, Carboxylic Acids Esters

• In addition to the four families of hydrocarbons,
  there are also many other families of organic
  molecules.
• These other families include elements other than
  carbon and hydrogen.
• They exhibit a wide range of chemical and
  physical properties.
• The families are distinguished by a group of
  atoms called a functional group

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Alcohols, Carboxylic Acids Esters

• Functional Group
• A functional group is an atom, group of atoms or
  bond that gives a molecule a particular set of
  chemical and physical properties

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Alcohols, Carboxylic Acids Esters

• The carbon-carbon double bonds found in alkenes
  is an example of a functional group.
• A chemical property of a double is that it will
  absorb hydrogen in the hydrogenation reaction.

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Alcohols, Carboxylic Acids Esters

• We look now at three families that are
  distinguished by a functional group that contains
  the element oxygen.
• Alcohols
• Members of the alcohol family contain a hydroxyl
  group.
• The hydroxyl group comprises an oxygen with one
  single bond to a hydrogen and another single bond
  to an alkane-type carbon

hydroxyl group
An alkane-type carbon atom
ethanol
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Alcohols, Carboxylic Acids Esters

• We look now at three families that are
  distinguished by a functional group that contains
  the element oxygen.
• Carboxylic acids
• Members of the carboxylic acid family contain a
  carboxylic acid group
• The carboxylic acid group comprises a hydroxyl
  group connected to a carbonyl group

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Alcohols, Carboxylic Acids Esters

• Carboxylic acids
• The present of the hydroxyl group next to the
  cabonyl group completely changes it properties.
• The alcohol hydroxyl group and the carboxylic
  acid hydroxyl group are chemically quite
  different, which is why molecules that have the
  carboxylic acid group are placed in a separate
  family from the alcohols.
• Later in the semester we will learn about some of
  these chemical differences.

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Alcohols, Carboxylic Acids Esters

• Carboxylic acids
• The carboxylic acid group can be attached to a
  hydrogen, an alkane-type carbon, or an
  aromatic-type carbon

propanoic acid
benzoic acid
methanoic acid (formic acid)
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Alcohols, Carboxylic Acids Esters

• We look now at three families that are
  distinguished by a functional group that contains
  the element oxygen.
• Esters
• Chemically, esters can be synthesized by reacting
  a carboxylic acid with and alcohol

carboxylic acid
alcohol
ester
water
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Alcohols, Carboxylic Acids Esters

• We look now at three families that are
  distinguished by a functional group that contains
  the element oxygen.
• Esters
• Chemically, esters can be synthesize by reacting
  a carboxylic acid with and alcohol

Ethyl propanoate
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Alcohols, Carboxylic Acids Esters

• Carboxylic acids
• The carboxylic acid group can be attached to a
  hydrogen, an alkane-type carbon, or an
  aromatic-type carbon

propanoic acid
benzoic acid
methanoic acid (formic acid)
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Alcohols, Carboxylic Acids Esters

• As we saw with the hydrocarbons, the physical
  properties of organic molecules depend on the
  noncovalent intermolecular interactions which
  attract one one molecule to another.
• With hydrocarbons, there is only one type of
  noncovalent interaction
• Induced dipole/Induced dipole (London dispersion
  force)
• The presence of the electronegative oxygen makes
  alcohols, carboxylic acids and esters polar
  molecules, these families, therefore, have at
  least two types of noncovalent interactions
• Induced dipole/Induced dipole (London dispersion
  force)
• Dipole/Dipole

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Alcohols, Carboxylic Acids Esters

• As we saw with the hydrocarbons, the physical
  properties of organic molecules depend on the
  noncovalent intermolecular interactions which
  attract one one molecule to another.
• Alcohols and Carboxylic acids also have a
  hydroxyl group with a hydrogen bonded to an
  oxygen. This allows them to form hydrogen bonds
  with each other. Therefore, carboxylic acids have
  at least three different noncovalent
  interactions
• Induced dipole/Induced dipole (London dispersion
  force)
• Dipole/Dipole
• Hydrogen bond

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Alcohols, Carboxylic Acids Esters

• To summarize, the types of noncovalent interact
  ions that each family can participate in include
• Hydrocarbons (Alkanes, Alkenes, Alkynes
  Aromatics)
• Induced dipole/Induced dipole (London dispersion
  force)
• Esters
• Induced dipole/Induced dipole (London dispersion
  force)
• Dipole/Dipole
• Alcohols Carboxylic acids
• Induced dipole/Induced dipole (London dispersion
  force)
• Dipole/Dipole
• Hydrogen bond

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Alcohols, Carboxylic Acids Esters

• These interactions are illustrated in Figure 4.23
  of your textbook.

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Alcohols, Carboxylic Acids Esters

• Boiling points are a good measure of the strength
  of the noncovalent interactions between
  molecules.
• The stronger the interactions, the higher the
  boiling point will be.
• Since all molecules have the London dispersion
  interaction, the boiling points of molecules is
  expected to increase with temperature.
• The next slide shows a chart using the data found
  in Table 4.7 of Raymond, in which the boiling
  points for alcohols, carboxylic acids and esters
  are plotted against molecular weight.

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Alcohols, Carboxylic Acids Esters

• As expected, the boiling points for members of
  all three families increases with molecular
  weight due to the London dispersion interactions.
• For a given molecular weight, the alcohols and
  carboxylic acids have a higher boiling point than
  esters, this is because they can form hydrogen
  bonds and esters cannot.
• The carboxylic acids have a slightly higher
  boiling point than alcohols, because they can
  form two hydrogen bonds with a neighboring
  molecule (See Figure 4.23 in Raymond)

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Alcohols, Carboxylic Acids Esters

• Another distinguishing characteristic of many of
  the families is odor.
• You nose is actually a highly sensitive chemical
  detector.
• The members of different families can interact
  differently with the receptors in your nose to
  produce smells that are characteristic of the
  families they belong to.
• For example
• Carboxylic acids produce the pungent, sometime
  unpleasant odors associated with ripe cheeses,
  rancid butter and vomit.
• Esters, on the other hand, produce the sweet,
  often pleasant order associated with flowers,
  perfumes and various natural and artificial
  flavorings. The next slide shows Figure 4.24 from
  Raymond, which gives some specific examples.

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Alcohols, Carboxylic Acids Esters

• Examples of some flavorable esters

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The End