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Chem 150 Unit 2 - Hydrocarbons

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Alkanes For a discusion on the structure of alkanes, see the Unit 2 Elaboration - Alkane Structure Alkanes Alkanes, along with the other hydrocarbons, are non-polar. – PowerPoint PPT presentation

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Title: Chem 150 Unit 2 - Hydrocarbons


1
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.

2
Organic Chemistry
  • Organic chemistry is the chemistry of carbon.
  • There are three forms of pure carbon
  • Diamond
  • Graphite

3
Organic Chemistry
  • Organic chemistry is the chemistry of carbon.
  • There are three forms of pure carbon
  • BuckminsterfullereneBucky Balls

4
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

5
Hydrocarbons
6
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.

7
Alkanes
  • Alkanes are hydrocarbons that contain only
    carbon-carbon single bonds.

8
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
9
Alkanes
  • For a discusion on the structure of alkanes,see
    the Unit 2Elaboration - Alkane Structure

10
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.

11
Alkanes
  • They interact with each other only through London
    dispersion forces.
  • Note how the boiling points increase with
    molecular weight.

12
Molecule in the News
13
Molecule in the NewsMelamine
14
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
15
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
16
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
17
Alkanes
  • For a discussion on naming alkanes,see the Unit
    2Elaboration - Naming Alkanes

18
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
19
Conformations
  • Carbon-carbon single bonds are free to rotate
  • This leads to different shapes for some molecules
  • These should not be confused with isomers.

20
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.

21
Conformations
  • All of the 3-dimensional models shown below are
    for the n-butane.
  • They were generated by rotating the central
    carbon-carbon bond.

22
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
23
Conformations
  • For a discussion on conformations,see the Unit
    2Elaboration - Conformations

24
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

25
Cycloalkanes
  • In naming these molecules, the prefix cyclo- is
    used to indicate the ring

26
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.

27
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.

28
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?

29
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

30
Alkenes, Alkynes Aromatic Compounds
  • Alkenes are hydrocarbons that contain at least 1
    carbon-carbon double bond.
  • Examples

31
Alkenes, Alkynes Aromatic Compounds
  • Alkynes are hydrocarbons that contain at least 1
    carbon-carbon triple bond.
  • Examples

32
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

33
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

34
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.

35
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.

36
Alkenes, Alkynes Aromatic Compounds
  • Naming of Aromatics is based on benzene
  • Aromatic compounds can contain multiple aromatic
    rings

37
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.

38
Practice Quiz 1 KEY
  • http//www.chem.uwec.edu/Chem150_S07/course/answer
    s/C150-Quiz-1-key.swf

39
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

40
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
41
Alkenes, Alkynes Aromatic Compounds
  • Like cycloalkanes, some alkenes can have cis and
    trans isomers

42
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

43
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

44
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.

45
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
46
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

47
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.

48
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)
49
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
50
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
51
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)
52
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

53
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

54
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

55
Alcohols, Carboxylic Acids Esters
  • These interactions are illustrated in Figure 4.23
    of your textbook.

56
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.

57
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)

58
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.

59
Alcohols, Carboxylic Acids Esters
  • Examples of some flavorable esters

60
The End
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