Organic Chemistry
Organic Chemistry
Organic Chemistry: The chemistry of carbon
and carbon-based compounds
Organic Chemistry in everyday life:
Smells & tastes: fruits, chocolate, fish, mint
Medications: Aspirin, Tylenol, Decongestants, Sedatives
Addictive substances: Caffeine, Nicotine, Alcohol
Hormones/Neurotransmitters: Adrenaline, Epinephrine
Food/Nutrients: Carbohydrates, Protein, Fat, Vitamins
Genetics: DNA, RNA
Consumer products: Plastics, Nylon, Rayon, Polyester
Organic Chemistry
• Also the “weed-out” class for pre-med
students!
• Notoriously difficult college class.
Question:
• What makes a molecule an organic molecule?
• The presence of carbon-hydrogen bonds!
The simplest hydrocarbons: Alkanes
• Compounds containing only C and H
• All bonds are single bonds
• Names end in -ane
6
Expanded and Condensed Structures
7
Structural Formulas
• “Lazy” way to write the Hydrogens
• Instead of drawing the bonds, just state how
many hydrogens are attached
• NOTE: The bonds are between CARBONS in a
parent chain, and not hydrogens!
Structural Formula
Expanded Structural formula
Names of Alkanes
The names of alkanes
• are determined by the IUPAC (International Union of Pure and
Applied Chemistry) system.
• end in –ane.
• with 1-4 carbons in a chain use prefixes as follows.
Name
# Carbons
Structural Formula
Methane
1
CH4
Ethane
2
CH3CH3
Propane
3
CH3CH2CH3
Butane
4
CH3CH2CH2CH3
9
Prefixes for # of Carbons
1
Meth
6
Hex
2
Eth
7
Hept
3
Prop
8
Oct
4
But
9
Non
5
Pent
10
Dec
Learning Check
A. Write the condensed formula for:
H
H
H
H
H
H
C
C
C
C
C
H
H
H
H
H
B. What is its molecular formula?
H
CH3─CH2─CH2─CH2─CH3
C5H12
(Gives total # of each atom, does not indicate how they are arranged)
C. What is its name?
pentane
11
ALKANES
(a “family” of hydrocarbons)
CnH2n+2
CH4
C2H6
C3H8
C4H10
etc.
What would be the formula for decane, which has 10 carbons?
Some Structures for Butane:
All these structures mean the same thing!
13
Cycloalkanes
Cycloalkanes
• are alkanes that form a loop.
• have two hydrogen atoms fewer than the open chain.
(remember each carbon has 4 bonds)
• Formula will be CnH2n
• are named by using the prefix cyclo- before the name of the
alkane chain with the same number of carbon atoms.
14
Examples of Cycloalkanes
Cyclopentane
CH2
CH2
CH2
CH2
CH2
Cyclohexane
CH2
CH2 CH2
CH2
CH2
CH2
15
Some Properties of Alkanes
Alkanes with 1-4 carbon
atoms are:
• methane, ethane, propane,
and butane.
• gases at room temperature.
• used as heating fuels.
16
Trivia question:
Can you name a famous propane
salesman?
(He also sells propane-related
accessories!)
Trivia question:
Can you name a famous propane
salesman?
Some Properties of Alkanes
Alkanes with 5-8 carbon atoms are
• liquids at room temperature.
• pentane, hexane, heptane, and octane.
• very volatile.
• used to make gasoline.
Alkanes with 9-17 carbon atoms
• are liquids at room temperature
• have higher boiling points.
• are found in kerosene, diesel, and jet fuels.
19
Combustion
In combustion reactions,
• alkanes react with oxygen.
• CO2, H2O and energy are produced.
Alkane + O2
CO2 + H2O + heat
20
Learning Check
Write a balanced equation for the
complete combustion of propane.
21
Isomers
• Compounds with the same formula, but
different structures
Are these isomers?
H H H H
H C C C C H
H H H H
Butane (C4H10)
H
H C
H
H
C
H C H
H
Isobutane (C4H10)
Structural isomers
• same molecular formulas
• different structural formulas
H
C H
H
Pentane C5H12
3 structural isomers
CH3 CH2 CH2 CH2 CH3
CH3
CH3
CH3 CH2 CH CH3
CH3
C CH3
CH3
•No other arrangements of C5H12 possible
Note
CH3
CH3
CH2 CH CH3
=
CH3 CH CH2 CH3
CH3
=
CH3
CH3 CH2 CH
CH3
etc.
Chemists needed to expand the system of nomenclature to
allow naming of individual structural isomers
•Compounds without branches are called ‘straight chain’ alkanes
•Branched compounds are named as derivatives of the longest
straight chain in the molecule
•The length of the longest chain provides the parent name
•The straight chain is numbered to allow indication of the point
of branching
•The branches are named from the corresponding alkanes
Naming the branches
Alkane
Alkyl group
Methane
Methyl (CH3-)
Ethane
Ethyl (CH3CH2-)
Propane
Propyl (CH3CH2CH2-)
Butane
Butyl (CH3CH2CH2CH2-)
Etc.
CH3
CH3 CH2 CH CH3
4
3
2
1
2-Methylbutane
[Straight chain numbered so as to give the lower branch number]
IUPAC rules for naming alkanes:
1. parent chain = longest continuous carbon chain  “alkane”.
2. branches on the parent chain are named as “alkyl” groups.
3. number the parent chain starting from the end that gives you
the lower number for the first branch (principle of lower
number).
4. assign numbers to the alkyl branches to show where they are in
the parent chain
5. if an alkyl group appears more than once use prefixes: di, tri,
tetra, penta…; each alkyl group must have a number!
6. the name is written as one word with the parent name last. The
names and locants for the alkyl branches are put in alphabetic
order (ignore all prefixes) separating numbers from numbers
with commas and letters from numbers with hyphens.
Step 1. Find the parent chain.
• Where is the longest continuous chain of
carbons?
Step 2. Number the parent chain.
• Number the parent chain so that the attached
groups are on the lowest numbers
Methyl is on carbon #2 of the parent chain
Methyl is on carbon #4 of the parent chain
1
5
1 8
2
4
3
3
4
2
3 6
7 2
8 1
4 5 5 4
6 3
5
1
GREEN is the right
way for this one!
27
1
7
2
6
3
5
4
4
Groups on 2 and 5
Groups on 4, 6, and 7
Groups on 2, 3, and 5
5
3
6
72
1
Groups on 3 and 6
Step 3. Designate where the group is
attached to the parent chain.
• Use the numbers of the parent chain from
step 2 to designate the location of the
attached groups to the parent chain.
2-methyl
1
2
3
4
5
CH3
CH3 CH2 C CH2 CH2 C CH2 CH3
CH2 CH2 CH3
H
CH3
First, identify longest straight chain
CH3
CH3
CH3 CH2 C CH2 CH2 C CH2 CH3
CH2 CH2 CH3
H
‘…nonane’
Number so as to give lower numbers for branch points
CH3
CH3
6
3
CH
C
CH2 CH3
CH3 CH2 C CH2
2
5
1
2
CH2 CH2 CH3
H 4
7
8
9
6-ethyl,3,6-Dimethylnonane
Branches at C3 and C6
Not at C4 and C7
Identical substituents grouped together with a prefix
•‘di…’ for two identical
•‘tri…’ for three
•‘tetra…’ for four
Substituents named in alphabetical order
CH3
CH3
CH3
C CH2 C CH3
H
CH3
2,2,4-Trimethylpentane
hexanes C6H14
IUPAC names
CH3CH2CH2CH2CH2CH3
hexane
CH3
CH3CH2CHCH2CH3
3-methylpentane
CH3
CH3CHCHCH3
CH3
2,3-dimethylbutane
CH3
CH3CHCH2CH2CH3
2-methylpentane
CH3
CH3CCH2CH3
CH3
2,2-dimethylbutane
Draw Some Simple Alkanes
• 3-ethylhexane
• 2,2-dimethylbutane
• 2,3-dimethylbutane
Alkanes
• Now that we know how to name
alkanes, let’s learn something about
their chemical properties.
Alkanes – chemical properties
• The main chemical property of alkanes is that they
have very low reactivity.
• Why? Know these two reasons:
1. Ionic and polar compounds tend to be more
reactive than non-polar compounds.
Non-polar compounds don’t attract other molecules
to react with.
2. C-C and C-H bonds are relatively strong. It takes a
lot of energy to break them.
Alkanes – chemical properties
•
The net effect is that alkanes have a fairly
restricted set of reactions.
You can:
1. burn them - destroying the whole molecule
2. react them with some of the halogens,
breaking carbon-hydrogen bonds;
3. crack them, breaking carbon-carbon bonds.
Cracking?
• Cracking is the name given to breaking up
large hydrocarbon molecules into smaller and
more useful bits.
Cracking
• There isn't any single unique reaction
happening in the cracker. The hydrocarbon
molecules are broken up in a fairly random
way to produce mixtures of smaller
hydrocarbons, some of which have carboncarbon double bonds. One possible reaction
involving the might be:
Alkanes – chemical properties
• One chemical reaction that alkanes will readily
undergo is combustion!
• CH4 is methane – a main component of natural gas.
Used to heat homes.
• C2H4 (ethane) is also a main component of natural
gas.
• C3H8 (propane) – sold as fuel for camp stoves
• C4H8 (butane) – used in lighters
• C8H18 (octane) – major component of gasoline
New topic: Functional Groups
Functional Groups
• As we’ve seen, alkanes don’t do much, except
burn.
• The chemistry of hydrocarbons is really
controlled by what is attached to the alkanes.
• Those attachments are called functional
groups.
Big Idea in Organic Chemistry
Structure controls Function
Each functional group has predictable reactivity
Types of Organic Compounds
Classified according to functional group
Alkane
Alcohol
Carboxylic acid
O
OH
OH
Alkene
Ether
Amine
NH2
O
Alkyne
C
Ketone
Amide
O
O
C
NH2
Haloalkane
Aldehyde
Amino acid
O
O
Cl
Br
H
H2N
OH
Naming Alkenes & Alkynes
Using the IUPAC alkane names:
Alkene names change the end to -ene.
Alkyne names change the end to -yne
Ignore the names in parentheses – those are the old-fashioned names from before the naming rules!
IUPAC Nomenclature for alkenes
• Parent is longest chain containing the double
bond.
• -ane changes to -ene.
• Number the chain so that the double bond
has the lowest possible number.
Chapter 7
48
Naming Alkenes & Alkynes
CH2= CH ─ CH2─ CH3
1
3
2
4
CH3─ CH=CH─ CH3
1
2
3
2
3
2
3
2-Methyl-2-butene
1
CH3─ CC ─ CH3
1
2-Butene
4
CH3
|
CH3─ CH=C─CH3
4
1-Butene
4
2-Butyne
Naming Alkenes & Alkynes
CH3─ CH2─ CC ─ CH3
5
4
3
2
2-Pentyne
1
CH3
CH3─ CH2─ C=CH ─ CH3
5
4
3
2
3-Methyl-2-pentene
1
CH2 – CH3
CH3─ CH2─ C=CH ─ CH3
5
4
3
2
1
3-Ethyl-2-pentene
Reactions of alkenes and alkynes
• The presence of a double or triple bond in a
hydrocarbon makes them much more
reactive.
• The double or triple bond indicates the
presence of extra electrons, providing a good
site for reactivity.
Addition reactions of alkenes and alkynes
• In addition reactions, a reactant is added to the two
atoms that form the multiple bond.
• Example: Reaction of ethene with bromine:
Addition of hydrogen:
• Hydrogenation
• Hydrogenation of alkenes produces the
corresponding alkanes.
CH2=CH2 + H2 → CH3-CH3
Hydrogenation
Notice that the reactant can hold extra hydrogens,
but the product is full of hydrogen.
Hydrogenation
• Hydrogenation turns unsaturated hydrocarbons into
saturated hydrocarbons
• Saturated?
• Remember what a saturated solution is? (It’s holding
all the solute it can possibly hold.)
• A saturated hydrocarbon is holding all the hydrogens
it can possibly hold.
• Saturated hydrocarbons are alkanes – no double or
triple bonds!
• Unsaturated hydrocarbons are alkenes or alkynes –
more hydrogen could be added.
Saturated and unsaturated
hydrocarbons
A related term: saturated fat
Saturated fats don’t have any double
bonds.
Monounsaturated fats have one double bond,
polyunsaturated have more than one double bond.
Saturated and unsaturated fats
• When one of the carbon bonds in the chain is a
double bond, there are two less hydrogens than
there would be in a saturated fat, so it is called a
mono-unsaturated fat. When there is more than one
double bond it is called a poly-unsaturated fat.
• Unsaturated fats are better than saturated because
the body can break them down easier and so they
are used more quickly in the body’s metabolism.
Structure - Alcohols
u
The functional group of an alcohol is
an -OH group bonded to a carbon
10-60
Nomenclature-Alcohols
IUPAC names
• the parent chain is the longest chain that contains the
OH group
• number the parent chain to give the OH group the
lowest possible number
• change the suffix -e to -ol
10-61
Name these:
CH3
CH3
CH CH2OH
2-methyl-1-propanol
OH
CH3
CH CH2CH3
2-butanol
CH3
CH3
C OH
CH3
2-methyl-2-propanol
Physical Properties
Alcohols are polar compounds
O
+
H
+C
H
H
H
So – is this alcohol soluble in water?
10-63
Solubility in Water
Solubility decreases as the size
of the alkyl group increases.
=>
10-64
Methanol
Can you draw the structure of methanol?
10-65
Ethanol
Distillation produces “hard” liquors
Denatured alcohol used as solvent
10% ethanol in gasoline
10-66
Chemical Properties of alcohols
10-67
Dehydration Reactions
An alcohol can be converted to an alkene by
dehydration.
Dehydration is just what is sounds like – removal
of water.
10-68
Dehydration of alcohols
CH 3 CH 2 OH
OH
H2 SO 4
180°C
CH 2 = CH 2
H2 SO 4
+
H2 O
+ H2 O
140°C
Cyclohexanol
CH 3
CH 3 COH
Cyclohexene
H2 SO 4
CH 3
2-Methyl-2-propanol
50°C
CH 3
CH 3 C= CH 2 +
H2 O
2-Methylpropene
10-69
As we’ve seen, alkanes have similar chemical properties, alkenes have
similar chemical properties, and alcohols have similar chemical properties.
Remember – it’s the functional group that controls the chemical properties.
10-70
One last example of a functional
group:
Ketones
10-71
Ketones:
Can you find the functional group?
10-72
Memory trick for ketones:
The ketone functional group looks like a key hole. Right?
10-73
Ketones:
Ketones are named by dropping the -e ending
of the parent name and adding -one.
5-methyl-3-hexanone
2-pentanone
10-74