Transcript Slide 1

Hydrocarbon Nomenclature
Organic Chemistry Lesson # 1
Introductory Terms
Organic – compounds that contain carbon bonded to each
other, hydrogen, and other specific non-metals like oxygen
and nitrogen.
• Exceptions include: carbonates (CO32-), cyanides (CN-),
carbides (C22-), and oxides of carbon (CO2, CO).
• The definition used to be any carbon compound, or any
compounds that support life.
Inorganic – any compound that does not contain carbon and
the exceptions listed above.
Organic Chemistry – the study of carbon-containing
compounds and their properties.
Introductory Terms
Hydrocarbon – a compound containing only carbon and
hydrogen atoms.
• They can be saturated, where all the bonds between
carbon atoms are single bonds, or unsaturated, where
there is at least one double or trip bond between carbon
atoms.
Functional Group – a group of atoms within a molecule that
determine the properties of the molecule, such as solubility or
reactivity.
• This could be as simple as a single atom or a type of
bond, or as complex as a group of atoms.
Why Carbon?
•Carbon
allows for the formation
of a large variety of compounds.
•Carbon atoms have the ability to
form 4 bonds.
•Carbon atoms may bind to form
chains, rings, spheres, sheets, and
tubes.
•Carbon atoms have the ability to
form single, double, and triple
bonds.
Alkanes
•The
simplest type of hydrocarbon, and is saturated with all single
bonds.
•Are in a chain structure (straight line).
•Methane is the simplest with only one carbon, which means it is
surrounded by 4 hydrogens. The bond angles between the
hydrogens are all 109.5° and it forms a tetrahedral shape. You
know methane as natural gas.
•Other common alkanes are propane and butane, which are used to
heat homes and fuel tools.
•Carbon-carbon single covalent bonds are held tightly together –
the bond is difficult to break. This is because there are no unpaired
electrons to participate in a reaction, therefore we say the bond is
unreactive.
•The general formula is CnH2n+2
First 5 Alkanes
Methane
-162°C
Ethane
-89 °C
Propane
-42 °C
Butane
0 °C
Pentane
36 °C
Alkanes
Homologous Series – in a group of compounds with the same
general formula, as the molar mass increases, a physical
property increases. In this case, boiling point. This is also
true of melting point.
• This has to do with intermolecular forces. The C-H bond
is non-polar as there is only a very small difference in
electronegativity. Weak London dispersion forces (also
known as Van der Waals forces) hold molecules together,
and the more atoms, the more forces exist.
• Chemists take advantage of the homologous series when
trying to separate a mixture of hydrocarbons in a
process called fractional distillation.
Cyclic Alkanes
•Hydrocarbons
that exist in an enclosed ring structure instead
of a chain.
•You need at least three carbons to form a cyclic structure.
•Rings of 3 or 4 tend to be reactive as they have small bond
angles, which are unstable.
•General Formula: CnH2n
Cyclopropane
Cyclohexane
Structural Isomers
•Structural
isomers are compounds that have the same
chemical formula but different structural formula.
•We can re-arrange the atoms in some straight-chained
hydrocarbons so that they exist as “branches”.
•Any attachment to a chain that replaces a hydrogen
atom is known as a substituent group. When the
replacement is carbon, it is specially known as an alkyl
group.
•Straight-chain and cyclic alkanes are not isomers of one
another as they have different general formulas.
Structural Isomers of…
1. Butane
2. Pentane
Drawing Practice
a) 3-methylpentane
b) 2,3-dimethylhexane
c) 4-ethyloctane
Drawing Practice
d) 1,4-dimethylcyclohexane
e) chlorobutane
f) 2,2-dibromopropane
Naming Practice
a)
CH2
CH2
H3C
CH
CH3
b)
H3C
CH3
CH CH
H2C
c)
CH2
H3C
CH3
CHHC
H3C
Cl
CH3
Naming Practice
d)
g)
CH3 CH3
H3C
C
C
CH2
e)
CH
CH
H2C
Br
CH
H2C
CH3
CH3
CH2
f)
H3C
CH2
HC
CH
CH3
CH2
CH2
CH
CH2
CH2
H3C
Br
Cl
CH3
CH
CH
CH2 CH3
CH3 CH3
H3C
CH3
CH3
Alkenes & Alkynes
•Two
unsaturated groups of hydrocarbons where at least one
double or triple bond exists in the parent chain. Alkenes
contain double bonds, and alkynes contain triple bonds.
•When double or triple bonds form between carbons they
become easier to break (triple bonds are weaker than double,
which are weaker than single). These bonds are said to be
reactive, as the double or triple can act as a “reaction centre”
(more on this later).
•The most simple alkene, ethene, is used in agriculture to help
ripen fruit faster, and ethyne is used in welding (its old name
is acetylene).
•Alkenes and alkynes are also non-polar.
Alkenes & Alkynes
General Formula for Alkenes: CnH2n
General Formula for Alkynes: CnH2n-2
Ethene
Propyne
Pent-2-ene
Naming & Drawing Alkenes/Alkynes
•Determine
the parent chain and the location of the
double or trip bond.
•When numbering the parent chain, begin with the end
closest to the multiple bond (instead of branches).
•Alkenes end in “ene”, alkynes end in “yne”, and the
numbering is between the prefix and suffix.
•If there is more than one multiple bond, the prefix di-,
tri-, etc. are used.
Drawing Practice
a) but-1-ene
b) hex-3-yne
c) 2,4-dimethylpent-2-ene
Drawing Practice
d) octa-2,4,6-triene
e) hepta-3,4-diene
f) 5-chlorohept-2-yne
g) 4-methylcyclopent-1-ene
Naming Practice
a)
CH2
C
C
CH2
H3C
CH2
CH3
HC
Br
b)
CH2
CH
CH
HC
CH2
c)
CH2
CH
H2C
CH3
CH
CH
CH3
Naming Practice
CH3
d)
H3C
CH
CH
HC
CH
CH2
CH3
H3C
H3C
e)
CH2 CH3
CH HC
C
CH2 CH2
HC
f)
CH2 CH3
H3C
CH
C
H2C
CH2
CH
CH3
Stereoisomers
•We
know already that structural isomers have the same
chemical formula but different structures.
•Stereoisomers have the same chemical formula formula
and structural backbone, but with a different
arrangement of atoms in space.
•An example common in double bonds is cis-trans
isomerism. A cis isomer is when two substituent groups
are located on the same side of a double bond, and a
trans isomer is when they are on opposite sides. This
gives rise to different physical properties.
Stereoisomers
•cis-pent-2-ene
trans-pent-2-ene
•cis-1,2-dichloroethene
trans-1,2-dichloroethene
Aromatic Hydrocarbons
•Alkanes,
alkenes, and alkynes are all called aliphatic
structures. They are structures based on branches or rings of
carbon structures.
•Aromatic hydrocarbons are unsaturated cyclic hydrocarbons
with a pattern of bonding that makes it chemically stable.
•The simplest aromatic hydrocarbon is benzene, with is a flat
6-carbon ring with alternating single and double bonds.
Although there are two types of bonds, chemical analysis has
show that the bond lengths are all equal. This is because the
double bonds alternate positions constantly (the electrons are
delocalized), making each carbon-carbon a 1.5 bond at any
given moment in time. This is known as a resonance structure
(more on this later).
Aromatic Hydrocarbons
•Aromatic
hydrocarbons can be liquids at room
temperature, or crystalline solids. They are symmetrical,
so they are non-polar, which means they tend to be
insoluble in water. Benzene is less reactive than alkenes.
Benzene was once widely used as a solvent, but it is now
known to be carcinogenic.
•General Formula: CnHn
Benzene:
Naming Aromatic Hydrocarbons
•A
benzene ring can be the main chain, or it can exist as a
branch. When a benzene is a substituent group (branch)
on a hydrocarbon chain, it is called a phenyl group.
•When benzene is the parent chain, number carbon 1 as
the branch in lowest alphabetical order.
Naming Practice
a)
Cl
b)
CH3
Br
CH2
CH3
CH3
c)
CH2
CH2
H3C
HC
CH3
Drawing Practice
a) 4,6-diphenyloct-2-ene
b) 1-ethyl-2,4-dimethylbenzene
c) 2phenylbut-2-ene
Summary
Alkanes
Alkenes
Alkynes
Aromatics
Saturated
Unsaturated
Unsaturated
Unsaturated
Single Bonds
Double Bonds
Triple Bonds
1.5 Bonds
End in –ane
End in –ene
End in –yne
End in –benzene
CnH2n+2
CnH2n
CnH2n-2
CnHn
Non-polar
Non-polar
Non-polar
Non-polar
Least reactive
More reactive
Most reactive
Less reactive
*Rings structure
use cyclo-
*Consider cis vs.
trans
*As substituent
use phenyl-