Organic means containing carbon.
Originally, scientists believed that
the only substances to contain
organic compounds were living
things as they were not able to
manufacture organic substances
in lab.
Why did nature choose carbon?
Carbon is not the most abundant element.
Nature chose carbon because of its versatility.
Forming covalent bonds, it is able to combine
with itself forming long chains, make
aromatic compounds, form isomers, and
combine with almost every other atom.
In drawing structural formulas of
organic substances you will notice
that carbon has four bonds. Each
line represents a carbon bond. Each
of these carbon bonds represents
two electrons being shared by the
two atoms. Carbon will have four
bonds, making it have 8 valence
electrons and a full outer shell.
One class of organic compounds are
hydrocarbons. These are substances
that contain only carbon and
hydrogen.
This is different from the
CARBOHYDRATES, which have C,H,O
in a 1:2:1 ratio.
There are a tremendous number of
hydrocarbons. Three types of hydrocarbons
we will study are the
Alkanes-these hydrocarbons contain only
single bonds between carbons
The formula for alkanes is CnH2n+2
Alkenes-an unsaturated hydrocarbon
containing at least one double bond
The simplest alkenes have one double
bond and the formula of CnH2n
Alkene - In general, a double bond is shorter in
length and stronger than a single bond.
If more than one double bond is present the
name changes. For example, two double
bonds would be a “diene”, three a “triene”.
Alkynes-are substances that have at least one
triple bond
The simplest alkynes have one triple bond
and follow the formula of CnH2n-2
The prefixes in organic chemistry are the same
for the alkanes, alkenes, and alkynes.
Meth-1
But-4
Hept-7
Eth-2
Pent-5
Oct-8
Dec-10
Prop-3
Hex-6
Non-9
Try these practice problems to test how well
you know the prefixes:
A. (Eth + Meth) X (Hept -Pent) =
B. (Oct + But)/Prop =
C. (Dec X Hex) - Non =
Eth
Answers next slide.
Answers:
A.
(2+1) X (7-5) = 6
B.
(8+4)/3 = 4
C.
(10X6)-9 = 25.5
2
If you look at alkanes, they can be anywhere
from one to one million atoms long. If the
carbon atoms are in a continuous line, the
substance is said to be “normal” so an N is
used to identify the substance. For example,
n-butane. This means you have a straight
chained 4 carbon alkane. If you have an
isomer of butane, it will have a different name
but it will not be n-butane.
Here you see
the first
compound is a
straight chain.
This would be
“normal
butane”. The
second
compound, an
isomer, is isobutane.
These are saturated hydrocarbons with the
general formula of:
CnH2n+2
This means that if you know the number of
Carbons, n, then the formula for the
hydrogens is H=2n + 2.
Alkanes are the only saturated
hydrocarbons. This is because
they have only single bonds
between each of the carbons.
If a double or triple bond is
added then the hydrocarbon
becomes UNSATURATED.
Now you can try these practice problems:
A. Calculate the number of hydrogens if an
alkane has 45 carbons.
B. How many hydrogens does an alkane
with 345 carbons have.
C. What is the molecular formula for
Heptane.
Answers next slide.
Answers:
H=2n+2
A. C45H92
B. C345H692
C. C7H16
Alkenes are UNSATURATED hydrocarbons that
contain at least one double bond.
Alkenes that have two double bonds are called
DIENES. An alkene with three triple bonds is
called a TRIENE.
Unless you are told otherwise, we will work
with alkenes that have ONE double bond.
The general formula for an alkene is as follows:
CnH2n
Notice that the +2 is missing from the alkane
formula. This is because with every carbon to
carbon bond made, you must lose 2H atoms.
Calculate the number of carbons or
hydrogens for each:
A. An alkene with 56 Hydrogens. C=?
B. An alkene with 56 Carbons. H=?
C. Give the formula for Butene.
Answers next slide.
Answers to previous slide:
H=2n
A. C28H56
B. C56H112
C. C4H8
These are also unsaturated hydrocarbons.
Alkynes differ from alkenes in that they
contain at least one triple bond between
carbons. This means that if you started with
an alkane, you would lose 4 hydrogens
making a triple bond. The resulting formula
would be:
CnH2n-2
Try these practice problems:
Calculate the number of C or H for each:
A. 34 carbon alkyne. H=?
B. An alkyne with 344 hydrogens. C=?
C. Give the molecular formula for Propyne.
Answers next slide.
Answers to previous slide:
H=2n-2 where n=no. of carbon
A. H=66
B.
C=173
C.
C3H4
Remember that in going from an alkane
to an alkene to an alkyne, you are
adding carbon to carbon bonds. Every
time you make a carbon to carbon
bond, you remove two hydrogen
atoms. If you remove a carbon to
carbon bond, you must add two
hydrogen atoms.
What would be the molecular formula if you
combined the following:
A. ethyne + pentene + butane
B. Octane + octyne
Answers next slide.
A. C2H2 + C5H10 + C4H10 so your initial
formula is C11H22. However, you have two
carbon to carbon bonds so you have to
substract 4 more hydrogens. The final
answer is C11H18.
B. C16H30