Organic Chemistry

Introduction to Organic Chemistry Of the more than 10+ million compounds that have been discovered, at least 90% are molecular compounds that contain Carbon. More than 1.4 million new molecules are discovered or synthesized each year and almost all of these are compounds of carbon.

History: In the early 19th Century, Swedish Chemist, Jons Jacob Berzelius classified into 2 categories:  Those from living things (organic)  Those from mineral sources (inorganic) Later, in 1828, Friedrich Wohler performed an experiment in which an inorganic molecule (ammonium cyanate, NH4OCN) was used to synthesize an organic molecule (urea, H2NCCCONH2). This marked the beginning of synthesizing organic molecules in a laboratory. Today, organic chemistry is defined as the study of the molecular compounds of carbon.

Compounds of Carbon: Hydrocarbons are organic compounds containing only the elements hydrogen and carbon. Hydrocarbons can be classified using the diagram below.

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Nomenclature of Hydrocarbons IUPAC rules are used to mane the tremendous number of different organic molecules. In this system, the following stems are used.

# of Carbon Atoms

Stem Name

Alkyl Group

Prefix Multiplier

1

meth

methyl

mono

2

eth

ethyl

di

3

prop

propyl

tri

4

but

butyl

tetra

5

pent

pentyl

penta

6

hex

hexyl

hexa

7

hept

heptyl

hepta

8

oct

octyl

octa

9

non

nonyl

nona

10

dec

decyl

deca

When you are working with organic compounds, three types of formulas can be used. 1. Molecular Formula: indicates the number of each type of atom in a molecule. For example: Hexane – C6H14. 2. Condensed Structural Formula: shows the number of hydrogen atoms bonded to each carbon atom in a molecule. For example: Hexane – CH3-CH2-CH2-CH2-CH2-CH3. 3. Structural Formula: indicates how hydrogen and carbon atoms are bonded and arranged using dashes for bonds.

Example: Hexane

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Alkanes Alkanes have the general formula CnH2n+2, where “n” is a whole number. All bonds between carbons are single bonds, and the molecule is saturated with hydrogen atoms.

Rules for Alkanes: 1.

For a straight chain alkanes, name the longest continuous chain of carbon atoms by naming the stem plus the suffix “ane”.

Example: Propane

* 2. For branched chain alkanes, number the carbon atoms of the longest continuous chain starting at the end closest to the branching. 3. Locate the branch by the number of the carbon atom to which it is attached on the main chain. 4. Name the branch. The braches are called alkyl groups and are named by using the appropriate stem plus the suffix “yl”. 5. If more than one of the same alkyl groups is present as branches, the number of these branches is indicated by the prefix multipliers. The location of a branch is identified with a number, using the lowest number.

Example: 2, 4 dimethyl hexane

6. If different alkyl groups are present as branches, assign the lowest number possible to each branch. The order of the branches is arranged alphabetically regardless of their number on the longest chain.

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Example: 4 ethyl, 2 methyl, heptane

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Alkenes Hydrocarbons which contain one carbon-carbon double bond are called Alkenes. All Alkenes have names ending in the suffix “ene”, indicating the presence of a carbon-carbon double bond. The general formula of the Alkenes is C2H2n. Example: Ethene

Rules for Alkenes: The rules for alkenes are similar to those for naming alkanes, with the following modifications: 1. The longest continuous chain must be chosen to contain both carbon atoms of the double bond, even if a longer chain could be found by choosing a different path. 2. The characteristic family suffice is “ene”. 3. The chain must be numbered from the end closest to a double-bonded carbon atom. If there is no difference, then it is numbered from the end closest to an alkyl group. 4. The position of the double bond is indicated by the lower-numbered carbon atom in the double bond, and this number is placed immediately before the stem. The number is omitted if there is only one possible location for the double bond.

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Questions for Alkenes 1. What is the structural formula for 2-methyl-1-butene?

2. What is the IUPAC name for the following?

Answer: 6-methyl-3-octene

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Alkynes Carbon and Hydrogen atoms can be arranged in many ways to produce a great variety of compounds. Yet another way involves triple bonds in the structure of compounds. This bond structure creates a class of aliphatic compounds called alkynes. Alkynes are aliphatic compounds that contain one or more triple bonds, and are similar to Alkenes, in that they are “unsaturated”. The general formula of the Alkynes is CnH2n-2.

Rules for Alkynes: The rules for Alkynes are the same as those for Alkanes: 1. The longest continuous chain must be chosen to contain both carbon atoms of the triple bond, even if a longer chain could be found by choosing a different path. 2. The characteristic family suffice is “yne”. 3. The chain must be numbered from the end closest to a triple-bonded carbon atom. If there is no difference, then it is numbered from the end closest to an alkyl group. 4. The position of the triple bond is indicated by the lower-numbered carbon atom in the triple bond, and this number is placed immediately before the stem. The number is omitted if there is only one possible location for the triple bond.

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Examples of Alkynes 1. 1-propyne

2. 4-methyl-2-hexyne

3. 4,6-dimethyl-2-octyne

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