Theory Exercises

Substituents of Organic Compounds

Alkanes are saturated hydrocarbons that contain only single bonds between carbon atoms. Their general formula is CₙH₂ₙ₊₂, where n represents the number of carbon atoms.

Branched Alkyl Radicals

NameFormulaStructure
Isopropyl-CH(CH₃)₂isopropyl
Isobutyl-CH₂CH(CH₃)₂isobutyl
sec-Butyl-CH(CH₃)CH₂CH₃sec-butyl
tert-Butyl-C(CH₃)₃tert-butyl
Neopentyl-CH₂C(CH₃)₃neopentyl

Halogens as Substituents

Halogens act as substituents and are named by adding the suffix "-o" to the element name:

ElementSubstituentSymbol
FluorineFluoro--F
ChlorineChloro--Cl
BromineBromo--Br
IodineIodo--I
Example: 2-chloropropane - A propane with a chlorine atom at position 2. 2-chloropropane

Aryl Groups

Aryl groups come from aromatic compounds. The most common is the phenyl group:

NameStructure
PhenylC₆H₅-
BenzylC₆H₅CH₂-
NaphthylC₁₀H₇-
Phenyl group

Other Common Substituents

NameFormula
Nitro--NO₂
Amino--NH₂
Hydroxy--OH
Methoxy--OCH₃
Ethoxy--OCH₂CH₃
Cyano--CN

Examples

1-chloro-2-methylbutane

1-chloro-2-methylbutane

A butane with a methyl group at position 2 and a chlorine atom at position 1.

2-phenyl-3-methylhexane

2-phenyl-3-methylhexane

A hexane with a phenyl group at position 2 and a methyl at position 3.

3-tert-butyl-2-methylpentane

3-tert-butyl-2-methylpentane

A pentane with a tert-butyl group at position 3 and a methyl at position 2.

4-bromo-2-chlorotoluene

4-bromo-2-chlorotoluene

A toluene (methylbenzene) with a bromine atom at position 4 and a chlorine atom at position 2.

3-ethyl-2-methylpentane

3-ethyl-2-methylpentane

If we number from the left, we have an ethyl at position 3 and a methyl at position 2. If we number from the right, we have an ethyl at position 3 and a methyl at position 4. The set (2,3) is lower than (3,4), so the first numbering is correct: 3-ethyl-2-methylpentane.