Transcript Organic Chemistry - Salisbury Composite High | Home

Organic Chemistry
Study of molecular compounds of
carbon
 Organic Compounds
–include all compounds of carbon except the oxides
(carbon dioxide, carbonate, carbide, cyanide, carbon
monoxide).
-3 to 4 million known organic compounds.
 Inorganic Compounds
-all other substances
-50,000 known inorganic compounds.
Two groups or organics:
 Hydrocarbons – compounds containing only
hydrogen and carbon. (ex. methane, butane, octane)
 Hydrocarbon derivatives – contain carbon,
hydrogen and at least one other element. (ex. organic
halides, alcohols, carboxylic acids, esters,
Unique Nature of Carbon
1. Carbon atoms have a bonding capacity of 4
2. Carbon atoms can bind together to form rings, sheets, tubes
and spheres of almost any size
3. Carbon can form single, double or triple bonds with other
elements (no other atom can do this)
Organic compounds are classified into
families based upon:
1. Types of bonds present (single, double, etc.)
2. Characteristic structures (rings, chains, branches)
3. Presence of functional groups (halogens (F, Cl, Br and I),
alcohols (OH), carboxylic acids (COOH), that determine
physical and chemical properties
4. Reactivity
Expressing Organic Compounds
Sometimes a shortened notation is used to describe certain
families of organic compounds:
R – indicates a chain of carbon and hydrogen
X – indicates a halogen F, Cl, Br, I
Organic diagrams
Complete structural diagram – shows all atoms / bonds.
Condensed structural diagram – omits CH bonds but shows C-C
bonds.
CH3 - CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH3
Line diagram – shows chains of carbon atoms with lines only where the
end of the line represents a carbon and its hydrogen atoms.
Organic Formulas
Molecular formulas – communicate which elements
are found in a compound.
Ex. CH4O
Structural formulas – communicate the arrangement of
atoms / functional groups in a compound.
Ex. CH3OH
Isomers
 are substances with the same molecular formula but
different structures, and therefore, different names.
Example: C6H14 has a number of isomers:
hexane
2- methylpentane
3- methylpentane
2,2 – dimethylbutane
Homologous Series
 is a sequence of molecules with similar structures and
differing only by the number of repeating units.
Examples: methane, ethane, propane, butane
Physical Properties within a
Homologous Series
 Melting point/boiling point – as the number of
carbons in the parent chain increases, melting point
increases.
Alkanes
 aliphatic compound.
 chains of single C-C bonds
 general formula is CnH2n+2.
 called saturated because they have the maximum number
of hydrogen atoms
 form straight chains or branched compounds.
Nomenclature (naming):
Prefixes are used to describe the number of carbon atoms
in a parent chain (longest) or in a branch.
1 = meth
2 = eth
3 = prop
4 = but
5 = pent
6 = hex
7 = hept
8 = oct
9 = non
10 = dec
Nomenclature of Straight Chain
Alkanes
 stem prefix indicates the number of carbons
 ending –ane indicates that it is a single bonded C-C chain.
Ex.
propane C3H8
pentane C5H12
Nomenclature of Branched Chain
Alkanes

longest continuous chain of carbon atoms is named as the
parent chain. (It doesn’t matter if the chain is not
straight)

Number the carbon atoms consecutively starting at the
end closest to the branch.

Number branch by the number of the carbon atom it is
on.

Name the branch using the prefix for the number of
carbons in the branch and the ending –yl before naming
the parent chain.
 If there are more than two branches, they are named in
alphabetical order (i.e. ethyl, methyl, propyl).
 If two branches are the same, use the prefixes di, tri, tetra,
etc to indicate the number of branches, and the carbon
numbers to indicate their locations.
Examples:
2- methylpentane
2,4 - dimethylhexane
3-ethyl-4-methylhexane
Alkenes and Alkynes
 Alkenes –contain one or more double C=C bonds. (two less H
for each double bond or CnH2n )
 Alkynes –contain one or more triple bonds.
(four less hydrogen for each triple bond or CnH2n-2)
 Both are said to be unsaturated because they do not contain the
maximum number of atoms possible
Nomenclature of Straight Chain
Alkenes and Alkynes
 longest or parent chain of carbon atoms must contain the
multiple bond, and the chain is numbered from the end closest
to the multiple bond.
 number that indicates the position of the multiple bond on the
parent chain is placed before the ene or yne ending in the parent
chain name.
 If there is only one possible position for the multiple
bond in the parent chain, it is not numbered.
 If there are two or more multiple bonds, they are
numbered with both positions and named with a prefix
indicating the number of multiple bonds.
Examples
ethyne
pent-2-ene
octa-1,7-diene
Naming Branched Chain Alkenes and Alkynes
 double / triple bond numbered with lowest numbers the
parent chain.
 the branches are named and numbered the same as they
were with the alkanes.
 Ex.
2,3 - dimethylpent-2-ene
Physical Properties of Aliphatics
 Non polar-do not dissolve in water, dissolve in benzene and
other non-polar solvents.
 As # of carbons increase, melting/boiling points increase due
to stronger London dispersion forces
Ex) small alkanes are gases (methane, propane, butane)
medium alkanes are liquids
large alkanes are waxy solids
 Boiling point of an alkene is lower than the alkane of the same
size (alkene has fewer atoms/electrons and weaker LDFs)
Ex) ethene b.p = -103.8oC vs ethane b.p = -88.6oC
 Boiling point of an alkyne is higher than the alkane of the same
size (nature of triple bond creates stronger bonds)
Cyclical Hydrocarbons
 part of the aliphatic group and
produce carbon rings.
 simple cyclo-alkanes have single
C-C bonds with no free ends.
The general formula is CnH2n.
 can have double or triple bonds
Naming Cyclical Hydrocarbons
 same as naming alkanes, alkenes and alkynes except the
parent “ring” begins with cyclo.
 If only one branched chain is present, it is not numbered
because it will always be considered to be on the first
carbon.
 For more than one branch, the first branch is on the first
carbon and the other branches are numbered so that the
second branch has the next lowest number.
Examples
 cyclobutene
 1,2 – dimethylcyclopentane
 propylcyclopentene
Aromatic Hydrocarbons
 originally thought to include compounds with an odor or
aroma.
 today are classified as compounds with a benzene ring structure.
Benzene Ring
 formula C6H6.
 a cyclical 6 carbon ring with each carbon being bonded to a
hydrogen atom.
 double and single bonds alternate around the ring, and shift
position, creates a hybrid exhibiting resonance, which is very
stable.
Naming Aromatic Compounds
 If an alkyl group is attached to a benzene ring, the
compound is named with a branch and the parent name is
benzene. No number is required if there is only one
branch.
 ethylbenzene
 for two or more branched chains, the first alphabetical branch
is numbered as carbon 1, and the next branches are given the
lowest numbers.
Ex. 1,4 – dimethylbenzene
 In some larger molecules, the benzene ring is a branch and
not attached to the end of a chain. In this case, the benzene
branch is given the name phenyl.
Ex. 2- phenylbutane