Unit-2-Hydrocarbons.ppt

Chem 150
Unit 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
• Buckminsterfullerene
“Bucky 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

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

Alkanes
For a discusion on the structure of alkanes,
see the Unit 2
Elaboration - 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
They interact with each other only through London dispersion
forces.
• Note how the boiling points increase with molecular weight.
Alkanes

13
Molecule in the News:Melamine

14
http://www.cbc.ca/health/story/2007/09/06/additives-lancet.html?ref=rss
http://www.medpagetoday.com/Psychiatry/ADHD-ADD/tb/6610
Organic Molecules in the News!!
Carmoisine
Quinoline yellow
Sodium benzoate

15
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?)
Alkanes
n-hexane
2-methyl-pentane 3-methyl-pentane 2,2-dimethylbutane 2,3-dimethylbutane

16
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.
Alkanes
n-hexane

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

18
When two or more molecules share the same molecular
formula, but have different atomic connections, they are
called constitutional isomers.
Constitutional Isomers
n-hexane

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

Conformations
For a discussion on conformations,
see the Unit 2
Elaboration - 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
In naming these molecules, the prefix cyclo- is used to
indicate the ring:
Cycloalkanes
As Parent Chain As Substituent Group

26
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.
Cycloalkanes

27
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.
Cycloalkanes

28
Questions
Draw the condensed structural formulas for the following
molecules:
A) 1-ethyl-2-methylcyclopentane
B) 1,1-dimethylcyclobutane
C) 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(2n+2)
• 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 are hydrocarbons that contain at least 1 carbon-
carbon double bond.
• Examples:

31
Alkynes are hydrocarbons that contain at least 1 carbon-
carbon triple bond.
• Examples:

32
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
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
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
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
Naming of Aromatics is based on benzene:
• Aromatic compounds can contain multiple aromatic rings

37
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/answers/C
150-Quiz-1-key.swf

39
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
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
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
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
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
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
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:
+
carbonyl group hydroxyl group carboxylic acid group

47
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.
+
carbonyl group hydroxyl group carboxylic acid group

48
Carboxylic acids
• The carboxylic acid group can be attached to a hydrogen,
an alkane-type carbon, or an aromatic-type carbon:
methanoic acid
(formic acid)
propanoic acid benzoic acid

49
Esters
• Chemically, esters can be synthesized by reacting a
carboxylic acid with and alcohol:
carboxylic
acid
alcohol ester water

50
Esters
• Chemically, esters can be synthesize by reacting a
carboxylic acid with and alcohol:
Ethyl propanoate

51
Carboxylic acids
• The carboxylic acid group can be attached to a hydrogen,
an alkane-type carbon, or an aromatic-type carbon:
methanoic acid
(formic acid)
propanoic acid benzoic acid

52
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:
• Dipole/Dipole

53
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:
• Dipole/Dipole
• Hydrogen bond

54
To summarize, the types of noncovalent interact ions that
each family can participate in include:
• Hydrocarbons (Alkanes, Alkenes, Alkynes &
Aromatics)
• Esters
• Dipole/Dipole
• Alcohols & Carboxylic acids
• Dipole/Dipole
• Hydrogen bond

55
These interactions are illustrated in Figure 4.23 of your
textbook.
alcohols
carboxylic acids
esters

56
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
• 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)
Molecular Weight {g/mol}
Boiling
Point
{°C}

58
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
Examples of some
flavorable esters:

Unit-2-Hydrocarbons.ppt

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