Introduction to Organic Chemistry Notes Sheet
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Organic Molecules
Functional Groups
– The following is a list of common functional groups
– OH
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– CO
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– COOH ____________
– NH2
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– SH
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– PO4
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– CH3
____________
Macromolecules
• Construction of Macromolecules
Dehydration Synthesis
Hydrocarbons – Naming
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Compounds containing just carbons and hydrogens are the most basic compounds
encountered in organic chemistry.
– hydrocarbons.
can be divided into three groups:
– those containing just single bonds
– those containing one or more double bonds
– those containing one or more triple bonds.
Before discussing how to name these compounds, it is instructive to examine how they
are represented by chemists
Drawing Hydrocarbons
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Recall - carbon makes four bonds and had the tetrahedral geometry
Consider the following representation of the molecule methane:
Alkane Nomeclature
Number of
Prefix Compound name
carbon atoms
1
2
3
4
5
6
7
8
9
Image
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Alkane nomenclature is straightforward;
difficulties come if one of the hydrogen or carbon atoms on the molecule is replaced by
another atom or group.
When this takes place, the group which replaces the hydrogen or carbon is called a
substituent.
Let's consider the situation in which one of the hydrogen atoms on an alkane has been
replaced by another alkane.
Consider the following molecule, 3-methypentane:
Long chain of five carbon atoms at the top of the image.
If this were all that composed the molecule, it would simply be called pentane.
However, one of the hydrogens on the carbon third from the end has been replaced
with an alkane, specifically methane.
How are we to name this molecule?
Alkane Nomeclature – Rules
1. First, we identify the longest chain of carbon atoms. We name this alkane. It will serve
as the root name for the molecule.
In the example above, the root name is __________________.
2. Next, we number the carbon atoms, starting at the end that gives the substituent the
lowest number.
In the example above,
3. Next, we name the substituent as if it were an independent alkane. However, we
replace suffix -ane with -yl. This name will serve as the prefix.
In the example above,
4. The compound is named "number-prefixrootname".
In the example above,
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What happens if the alkane has more than one substituent?
In this case, the rules above are followed, and the carbons on the longest chain are
numbered to give the lowest number possible to one of the substituent.
The substituents are then all named in the prefix (e.g. 2-ethyl,3-methyl).
If more than one substituent is attached to the same carbon atom, the number of that
carbon atom is repeated to indicate the number of substituents and the prefixes di- (2)
or tri- (3) are used.
If there are more than one substituent on different carbon atoms, the prefixes are
ordered alphabetically (e.g. ethene before methane).
The prefixes di- and tri- are ignored when considering alphabetical order. Consider the
following compound:
Alkene Nomenclature
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Alkenes are hydorcarbons containing one or more ______________.
Alkenes are named using the same general naming rules for alkanes, except that the
suffix is now -ene. There are a few other small differences:
Alkyne Nomeclature
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Hydorcarbons containing one or more triple bonds are called Alkynes.
Alkynes are named using the same general procedure used for alkenes, replacing the
suffix with -yne.
If a molecule contains both a double and a triple bond, the carbon chain is numbered
so that the first multiple bond gets a lower number.
If both bonds can be assigned the same number, the double bond takes precedence.
The molecule is then named "n-ene-n-yne", with the double bond root name preceding
the triple bond root name
– (e.g. 2-hepten-4-yne).
Functional Group Nomenclature
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Alkanes are extremely ____________________
Carbon-carbon and carbon-hydrogen bonds are among the most stable bonds in
chemistry
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We have already encountered two functional groups. The double bonds in alkenes and
the triple bonds in alkynes are able to undergo reactions that the single bonds in
alkanes cannot.
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There are several other significant functional groups, summarized in the table below.
Note that in organic chemistry, the letter "R" represents any alkane, and the letter "X"
represents any halogen.
– Functional group Structure
– Alkyl halide
– Alcohol
– Ether
– Amine
Naming Alkyl Halides
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One of the simplest functional groups is the alkyl halide.
In an alkyl halide, one of the hydrogen atoms in an alkane has been replaced by a halogen.
– What are halogens again?
Alkyl halides are easy to name;
– name of the alkane is preceded by the number of the carbon on which the halogen is
substituted and the name of the halogen,
– modified so that -ine is replaced by -o (e.g. 2-bromopropane).
If a molecule also contains a multiple bond, numbers are assigned to give the lowest number
to the first functional group. In the event of a tie, the lowest number goes to the multiple bond.
Naming Alcohols
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The alcohol is a very common functional group and a very easy one to name.
The molecule is named as if it were an alkane (or alkene or alkyne)
– except that the suffix -ane is replaced by -ol
– and the number of the carbon atom on which the -OH group is located is placed
before the name of the compound (e.g. 2-butanol).
The alcohol functional group takes precedence over alkyl substituents, multiple bonds,
and halides and always gets the lowest number.
Naming Ethers
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An ether is a molecule consisting of two alkyl groups connected to an oxygen atom.
Ethers are named by considering one alkyl group (the shorter one) plus the oxygen
atom to be a substituent and the other alkyl group (the longer one) to be an alkane.
The alkyl group plus oxygen atom is called an "alkoxy" substituent and is named by
replacing -ane suffix from the alkane with -oxy (e.g. methane becomes methoxy).
The allkoxy substituent gets priority over alky and halide substituents, but not over
alcohols, which will get the lower number.
Naming Amines
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An amine is a derivatives of the molecule ammonia, NH3, in which one or more of the
hydrogens has been replaced by an alkyl substitutent (R group).
Amines are named by treating the amino group as a substituent and giving it the name
"amino" (e.g. 2-aminobutane).
If multiple hydrogens have been replaced by alkyl substituents, then these alkyl
substituents are stated before the word "amino" (e.g. 2-dimethylaminobutane).
Cyclohexanes
• The alkanes we have studied so far have been of two types: linear and branched. There is
a third type of alkane in which the molecule does not have ends but instead forms a ring.
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Stable cycloalkanes cannot be formed with carbon chains of just any length.
Recall that in alkanes, carbon adopts the tetrahedral geometry in which the angles
between bonds are 109.5°.
• For some cylcoalkanes to form, the angle between bonds must deviate from this ideal
angle, an effect known as angle strain.
• Additionally, some hydrogen atoms may come into cloeser proximity with each other than
is desirable (become eclipsed), an effect called torsional strain.
• These destabilizing effects, angle strain and torsional strain are known together as ring
strain.
• The smaller cycloalkanes, cyclopropane and cyclobutane, have particularly high ring
strains because their bond angles deviate substantially from 109.5° and their hydrogens
eclipse each other.
• Cyclopentane is a more stable molecule with a small amount of ring strain, while
cyclohexane is able to adopt th perfect geometry of a cycloalkane in which all angles are
the ideal 109.5° and no hydrogens are eclipsed; it has no ring strain at all.
• Cycloalkanes larger than cyclohexane have ring strain and are not commonly encountered
in organic chemistry.
• Most of the time, cyclohexane adopts the fully staggered, ideal angle chair conformation
In the chair conformation, if any carbon-carbon bond were examined, it would be found to
exist with its substituents in the staggered conformation and all bonds would be found to
possess an angle of 109.5°.
Methylcyclohexanes
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Methylcyclohexane is cyclohexane in which one hydrogen atom is replaced with a methyl
group substituent.
Methylcyclohexane can adopt two basic chair conformations: one in which the methyl
group is axial, and one in which it is equatorial.
Methylcyclohexane strongly prefers the equatorial conformation.
In the axial conformation, the methly group comes in close proximity to the axial
hydrogens, an energetically unfavorable effect known as a 1,3-diaxial interaction
Thus, the equatorial conformation is preferred for the methyl group. In most cases, if the
cyclohexane ring contains a subsituent, the substituent will prefer the equatorial
conformation.