Transcript Introduction to Organic Chemistry

Introduction to Organic
Chemistry
Yes!!
I can’t wait!!!
I hear everyone fails this in college!!!
Intro - Organic Molecules
• Living things are composed of organic molecules,
which means that they contain carbon
– carbon has four electrons in outer shell which can bond with
other atoms
– carbon can be linked to other carbons or atoms such as
hydrogen (H), oxygen (O) and nitrogen(N)
– long links of these carbons can form into chains or rings
– Some organic molecules ONLY contain linked carbons and
hydrogen ---->hydrocarbons (ex: methane)
– living organisms tend to be composed of very long and
unreactive carbon chains (unlike methane, which is very
reactive!)
Intro – Functional Groups
• In organic chemistry, molecules with similar properties
are grouped together
– These all have similar groups of atoms, and these groups of
atoms are called functional groups
– Functional groups can provide physical and chemical properties
such as polarity and acidity (ex; carboxyl, -COOH, is a weak
acid)
– Most reactions in living organisms involves the transfer of
a functional group from one molecule to another
– The following is a list of common functional groups
• OH
Hydroxyl
• CO
Carbonyl
YOU MUST
• COOH
Carboxyl
MEMORIZE THIS
• NH2
Amino
LIST!!!
• SH
Sulfhydryl
• PO4
Phosphate
• CH3
Methyl
Intro – Functional Groups
Intro –
Functional
Groups
Intro - Macromolecules
• Construction of Macromolecules
– many macromolecules are polymers, which means that
they are constructed of many linked identical or similar
subunits
– How are macromolecules made? Remove an OH from
one molecule, and an H from another molecule
• this requires energy
• it is called dehydration synthesis (do you see the
water above?!)
• in living organisms, enzymes assist in these reactions
– Macromolecules are disassembled in the opposite way, by
adding a water molecule (OH added to one, H to another
subunit)
• this releases energy
• a reaction of this type is called a hydrolysis
Intro - Dehydration Synthesis
Hydrocarbons - Naming
• 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
• Recall - carbon makes four bonds and had the tetrahedral geometry
– only two bonds can occupy a plane simultaneously.
– The other two bonds point in back or in front of the plane.
– In order to represent the tetrahedral geometry in two dimensions
• solid wedges are used to represent bonds pointing out of the plane of the
drawing toward the viewer
• dashed wedges are used to represent bonds pointing out of the plane of the
drawing away from the viewer
• Consider the following representation of the molecule methane:
• Two dimensional representation of methane
Drawing Hydrocarbons
• it can be time-consuming to write out each atom and bond
individually.
• hydrocarbons can be represented in a shorthand notation called a
skeletal structure.
• only the bonds between carbon atoms are represented.
• Individual carbon and hydrogen atoms are not drawn
• bonds to hydrogen are not drawn.
• If the molecule contains just single bonds; drawn in a "zig-zag"
fashion.
• This is because in the tetrahedral geometry all bonds point as far
away from each other as possible, and the structure is not linear.
representations of the molecule propane:
• Full structure of propane
Skeletal structure of propane
Drawing Hydrocarbons
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Only the bonds between carbons have been drawn, and these have been
drawn in a "zig-zag" manner.
no evidence of hydrogens in a skeletal structure.
in the absence of double or triple bonds, carbon makes four bonds total, the
presence of hydrogens is implicit.
Whenever an insufficient number of bonds to a carbon atom are specified in
the structure, it is assumed that the rest of the bonds are made to
hydrogens.
For example:
– if the carbon atom makes only one explicit bond, there are three hydrogens
implicitly attached to it.
– If it makes two explicit bonds, there are two hydrogens implicitly attached, etc.
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•
Two lines are sufficient to represent three carbon atoms.
It is the bonds only that are being drawn out & it is understood that
there are carbon atoms (with three hydrogens attached!) at the
terminal ends of the structure.
Alkane nomenclature
• When hydrocarbons contain only single bonds,
they are called alkanes.
• Alkanes are named using a prefix for the
number of carbon atoms they contain, followed
by the suffix -ane.
Number root
example
Structure
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1
2
3
4
5
6
7
8
9
methethpropbutpenthexheptoxnon-
methane
ethane
propane
butane
pentane
hexane
heptane
oxane
nonane
(see board)
Alkane nomenclature
• 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:
Alkane nomenclature
• 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 nomenclature - 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 pentane.
2.
Next, we number the carbon atoms, starting at the end
that gives the substituent the lowest number.
In the example above, we can count from either end and arrive
at 3 for the substituent.
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, methane is the substituent, so we call it
methyl.
4.
The compound is named "number-prefixrootname".
In the example above, the name is 3-methylpentane
Alkane nomenclature - Rules
• 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:
Alkane nomenclature
• The longest carbon chain has seven carbon
atoms, so the root name is heptane.
• Numbering from the right gives the lowest
number to the first substituent.
• There are two methyl substituents at the second
carbon atom, so we use the prefix 2,2-dimethyl.
• There is another substituent on the fourth
carbon atom, so we use the prefix ethyl.
• Ethyl comes before methyl alphabetically, so we
name the compound
4-ethyl-2,2-dimethylheptane.
Alkene Nomenclature
• Alkenes are hydorcarbons containing one or more
double bonds.
• 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:
– The main chain of carbon atoms must contain both carbons in
the double bond.
– The main chain is numbered so that the double bond gets the
smallest number.
– Before the root name, the number of the carbon atom at which
the double bond starts (the smaller number) is written.
– If more than one double bond is present, the prefixes di-, tri-,
tetra-, etc. are used before the -ene, and (strangely) the letter "a"
is added after the prefix for the number of carbon atoms.
Alkyne Nomeclature
• 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
• Alkanes are extremely unreactive.
• Carbon-carbon and carbon-hydrogen bonds are among the most
stable bonds in chemistry
• alkanes serve as a backbone or template on which unreactive
carbon or hydrogen atoms can be replaced by substituents
consisting of more reactive atoms or groups of atoms.
• A substitient consisting of an atom or group of atoms other than
carbons and hydrogens is called a functional group.
• Functional groups are significant because they are the part of the
molecule that undergoes reactions.
• One functional group may change into another one, or a functional
group might react with a separate molecule to build up a larger
structure.
• Functional groups are the essential
"reacting units" in organic chemistry.
Functional Group Nomenclature
• 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.
• 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 groupStructure
– Alkyl halide
R-X
– Alcohol
R-OH
– Ether
R-O-R
– Amine
NR3
Naming Alkyl Halides
• 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
• 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
• 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
• 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. 2dimethylaminobutane).
Cycloalkanes
• 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.
• These molecules are called cycloalkanes
Figure 1: Skeletal structure of cyclohexane, a
cycloalkane
Cycloalkanes
• 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.
Cycloalkanes
• 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.
Cyclohexane
• Most of the time, cyclohexane adopts the fully staggered,
ideal angle chair conformation (Figure 2).
• 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°.
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Methylcyclohexane
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.
OUCH!!!
• Stop please stop my head is hurting and I
am pretty sure my brain is bleeding?
• Do we really have to know all of this for
the test?
• Will I really have to know all of this for the
future in organic chemistry?
• Can I quit now and just become a
Kindergarten teacher?