Hydrocarbons
Organic Chemistry
• Organic chemistry is the study of
carbon-containing compounds –
carbon chemistry
• Until early 19th century, it was
thought that all organic
compounds were formed from
living organisms
• This changed when Friedrich
Wöhler, “father of organic
chemistry”, synthesized urea in
the laboratory in 1828
(Urea is a waste product of protein
breakdown in the body)
http://www.pharmaceutical-journal.com/opinion/blogs/father-of-organic-chemistry/11132874.blog
The Chemistry of Carbon
• Number of carbon-containing compounds are
very high – Why?
• 1) Carbon can form (up to 4) stable covalent
bonds with other carbon atoms
• 2) Carbon atoms can form stable bonds with
other elements (oxygen, nitrogen, sulfur,
halogens)
• 3) Carbon can form double and triple bonds with
other carbon atoms to form various organic
compounds with different properties
Groups of Organic Compounds
http://www.masterorganicchemistry.com/2010/10/06/functional-groups-organic-chemistry/
Hydrocarbons
(only C and H)
Aliphatic
Aromatic
(ring with
conjugation)
(open chain and
ring without
conjugation)
Alkanes
Cycloalkanes
Alkenes
Alkynes
Alkanes
• Alkanes are saturated
hydrocarbons – they contain only
carbon-carbon and carbonhydrogen single bond
• CnH2n+2 is the general molecular
formula for alkanes
• All hydrocarbons are nonpolar
molecules – not soluble in water
• They are soluble in nonpolar
organic solvents
• They have relatively low melting
and boiling points and lower
density then water
• As the hydrocarbon chain gets
longer, melting and boiling point
increases
http://www.meta-synthesis.com/webbook/06_ligands/ligand.html
http://www.revisescience.co.uk/2011/schools/sspp/sc1mhc3.asp
Alkyl groups
• Alkyl groups are
alkanes with one
fewer hydrogen
atom
• Methane, methyl
propane, propyl
• Used to indicate
hydrocarbons as
substituents
Table for Common Alkane Parent Chains
Number of Carbon Atoms
Name of alkane
Name of alkyl group
1
methane
methyl
2
ethane
ethyl
3
propane
propyl
4
butane
butyl
5
pentane
pentyl
6
hexane
hexyl
7
heptane
heptyl
8
octane
octyl
9
nonane
nonyl
10
decane
decyl
16
hexadecane
hexadecyl
18
octadecane
octadecyl
Naming Alkanes
• Many common organic compounds are
named historically by the name of the
person who discovered it or by a name
that reflects the source of the compound
• Penicillin (Penicillium notatum), aspirin
• As the number of organic compounds
increased, the need for a systematic
nomenclature was realized
• IUPAC (The International Union of Pure
and Applied Chemistry) – the
organization responsible for establishing
and maintaining a universal
nomenclature system
(IUPAC Nomenclature System)
Penicillin core
aspirin
IUPAC Rules for Naming Alkanes
• 1) Determine the name of the parent
compound – the longest continuous carbon
chain in the compound (use the table)
pent – ane (related to number + ane)
• 2) Number the carbons in the parent
compound from one end such that the first
substituent encountered takes the lowest
possible number
• 3) Name and number each of the substituents
on the parent compound (alkyl or halogen
substiuents)
• 4) If the same substituent occurs more then
once, a separate position number is given for
each (di-, tri-, tetra-, etc.)
• 5) Place the name of the substituents in
alphabetical order before the name of the
parent compound – numbers are separated by
commas and numbers are separated from
names by hyphen (-)
2,3-Dimethylhexane
3-Fluoro-2,4-dimethylhexane
(halogens are placed before alkyl substituents)
Constitutional Isomers
• Isomers that have the same molecular
formula, but different connectivity of its
atoms
• They have different physical and chemical
properties
http://www.sparknotes.com/chemistry/organic2/alkanes/section2.rhtml
Cycloalkanes
• Saturated hydrocarbons that have a ring structure
are called cycloalkanes
• Cycloalkanes – similar to alkanes – are saturated;
all C-C bonds are single bonds
• They have the general molecular formula of CnH2n
(two less hydrogen then open chain alkanes)
http://en.wikibooks.org/wiki/Organic_Chemistry/Cycloalkanes
Naming Cycloalkanes
• 1) Determine the name of the alkane with
the same number of carbon atoms in the
ring and add the prefix cycloCyclopentane, cyclohexane etc.
• 2) If there is only one substituent, place
the name of the substituent before the
name of the cycloalkane
(methylcyclohexane, chlorocyclohexane)
• 3) If there are more then one substituent,
use numbers to give the lowest possible
position number (1-ethyl-2-methyl
cyclohexane)
(1-ethyl-2-methyl cyclohexane)
Cis-trans Isomerism in Cycloalkanes
• Cis-trans isomerism is a type of geometric isomerism
(stereoisomers)
• This isomerism is due to lack of free rotation around
the bonds (energy barrier) – substituents are either
above or below the ring
• They have different physical properties
Reactions of Alkanes:
1) Combustion
• Oxidation (burning) of hydrocarbons in the
presence of excess oxygen is called combustion
• The reaction produces CO2, water and releases
large amounts of heat
• Fuels are hydrocarbons (methane, natural gas,
gas used for vehicles, petroleum etc.)
• CH4 + 2O2  CO2 + 2H2O + heat energy
• Some organisms use this reaction to produce
energy
2) Halogenation
• Reaction of an alkane with a halogen (chlorine or bromine
usually) to produce an alkyl halide (or haloalkane) and a
hydrogen halide
• This reaction occurs through substitution mechanism
• This reaction converts unreactive alkanes to reactive alkyl
halides, which are starting materials for synthesis of many
organic compounds, including pharmaceuticals
• This reaction requires heat and/or light:
CH4(g) + Cl2(g)
CH3Cl(g) + HCl(g)
(Multiple halogenations can also occur if the reaction is
allowed to continue)
Unsaturated Hydrocarbons
• Unsaturated hydrocarbons
contain at least one carboncarbon double bond or triple
bond
• Alkenes (double bond), alkynes
(triple bond) and aromatic
compounds (double bonds in a
ring) are all groups of unsaturated
hydrocarbons
• Many of the medically important
molecules are characterized by
their saturation/unsaturation; for
example fatty acids can be either
saturated or unsaturated
http://www.revisescience.co.uk/2011/schools/sspp/sc1mhc3.asp
Alkenes and Alkynes
•
•
•
•
•
•
•
Unsaturated hydrocarbons
Alkenes: at least one double bond
Alkynes: at least one triple bond
Carbons in an alkane are bonded to 3 other atoms (hydrogen or carbon) –
tetrahedral-109.5
Carbons of the double bond are bonded to two other atoms – 120 degree –
planar
Carbons making up the triple bond is connected to only one other atom – 180 –
linear
Like alkanes, alkenes and alkynes are nonpolar, not soluble in water, soluble in
nonpolar solvents – they have all similar melting and boiling points
http://commons.wikimedia.org/wiki/File:Angles_of_Alkane_Alkene_Alkyne.png
Nomenclature of Alkenes and Alkynes
IUPAC Rules:
• 1) Name the longest continuous carbon
chain (alkane parent compound)
containing the double or triple bond
• 2) Replace the –ane ending of the name
with –ene for alkene and
–yne for alkyne
• 3) Number the chain such that you give
the lowest possible number for the first of
the two carbons containing the double
bond or triple bond
• 4) Determine the number and name of
the substituents (the groups bonded to
the parent chain); double and triple bond
carbons get lower numbers compared to
alkyl and halogen substituents
• 5) Alkenes with more than one double
bond as alkadienes, alkatrienes etc.
3,4-Diethyl-1-hexene
3-Chloro-1,4-pentadiene
http://chem4three.blogspot.com.tr/2011/05/alkenes-and-alkynes-double-and-triple.html
Cis-trans (Geometric) Isomers
• Rotation around the carbon-carbon double
bond is restricted (requires very high energy –
not possible at room temperature)
• This is due to pi-bonding and shape of orbitals
http://chemistry.tutorvista.com/organic-chemistry/isomers.html
Cis versus Trans Fatty Acid
• Most unsaturated fatty acids in the body are cis isomers,
• Trans isomers (found in margarines) are harmful for health
Reactions of Alkenes and Alkynes
• The most important reaction of alkenes is
addition reactions to the carbon-carbon
double bond
1) Hydrogenation
2) Halogenation
3) Hydration
4) Hydrohalogenation
1) Hydrogenation
• Addition of a molecule of
hydrogen (H2) to the double
bond to give an alkane
• Platinum, palladium or nickel are
required as catalyst – heat and
pressure also might be required
• Alkynes are hydrogenated in a
similar way to alkenes (2
molecules of hydrogen molecule
is needed to convert an alkyne to
an alkane)
• Hydrogenation is used in food
industry to convert vegetable
oils (liquid) to margarine (solid) unsaturated oils are converted
into saturated fat
http://chemwiki.ucdavis.edu/Organic_Chemistry/Hydrocarbons/Alkenes/Reactions_of_Alkenes/Catalytic_Hydrogenation
2) Halogenation: Addition of X2
• Chlorine (Cl2) or bromine (Br2) can be added to a
double bond – proceeds easily, no need for
catalyst
• Bromine test:
• Red color of bromine in solution is lost if bromine
is added to the double bond
• Alkynes react the same way as alkenes
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch06/ch6-7.html
3) Hydration: Addition of H2O
• A water molecule can be added to an alkene double bond in the
presence of trace acid
hydrogen (-H) adds to one carbon, -OH adds to the other carbon
• The product of hydration reaction is an alcohol
• When an unsymmetrical alkene is hydrated, there are more than
one product possible; how to know the major product?
• Markovnikov’s Rule: Among the two carbon atoms making the
double bond, the carbon with more hydrogen atoms attached
prefers receiving the hydrogen and the other carbon gets –OH
• Hydration is an important type of reaction in biological systems
4) Hydrohalogenation: Addition of HX
• Hydrogen halides (HBr, HCl, HI) can also be
added to an alkene; the product is an alkyl
halide
• This reaction also follows Markovnikov’s rule:
Hydrogen adds to the double bond carbon
with more hydrogen, halide adds to the
double bond carbon with less hydrogen