3.1 Introduction To Organic Chemistry

• Shows the simplified organic formula, shown by removing hydrogen atoms from alkyl chains • leaving just a carbon skeleton and associated functional groups.

Straight-chain organic molecules are those in which the carbon atoms are connected to each other in one continuous chain Pentane is a straight-chain organic molecule as the carbon atoms are connected in one continuous chain

Branched organic molecules have side groups attached to the main chain of carbon atoms 2-methylbutane is a branched organic molecule as the main chain (consisting of 4 carbon atoms) has a methyl branch

Cyclic organic molecules are those in which the carbon atoms are connected to each other in a ring shape Cyclopentane is a cyclic organic molecule as the carbons are attached to each other in a ring structure

Structural isomers are compounds that have the same molecular formula but different structural formulae E.g. propene and cyclopropane

• Chain isomerism • Positional isomerism • Functional group isomerism

• Chain isomerism is when compounds have the same molecular formula, but their longest hydrocarbon chain is not the same • This is caused by branching E.g. pentane and 2,2-dimethylpropane Both compounds are made up of the same atoms, however the longest carbon chain in pentane is 5 and in 2,2-dimethylpropane it is 3 (with two methyl branches)

• Positional isomers arise from differences in the position of a functional group in each isomer • The functional group can be located on different carbons • For example, butan-1-ol and butan-2-ol Both compounds have an alcohol group and are made up of 4 carbons, 10 hydrogens and one oxygen, however in butanol the functional group is located on the first carbon and in 2-butanol on the second carbon

• When different functional groups result in the same molecular formula, functional group isomers arise • The isomers have very different chemical properties as they have different functional groups • For example, butanol and ethoxyethane Both compounds have the same molecular formula however butanol contains an alcohol functional group and ethoxyethane an ether functional group

• Step 1: Draw the structural formula of the compound • Step 2: Determine whether it is a stereo or structural isomer • Step 3: Determine whether it is a functional group, chain or positional isomerism

Stereoisomers are compounds that have the same atoms connected to each other, however the atoms are differently arranged in space • Molecules with the same structural formula • But the atoms are arranged differently in space

• E/Z nomenclature is used to distinguish between the isomers • Z isomers have functional groups on the same side of the double bond/carbon ring • E isomers have functional groups on opposite sides of the double bond/carbon ring • To discuss E / Z isomers, we will use an alkene of the general formula C2R4: • You may see this type of isomerism referred to in other sources as cis/trans isomerism • This is a special case of E/Z isomerism • A “cis” isomer would essentially be the same as a “Z” isomer and a “trans” isomer would also essentially be the same as an “E” isomer

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