Chemistry Nomenclature: Alkyl Groups, Cycloalkanes, and Halogen Substituents (Last-Minute Review)

Determine the parent: longest carbon chain or ring; for rings, cycloalkane can be the parent when appropriate.
Substituents use the -yl form: methyl, ethyl, propyl, butyl, etc.
Attach substituents to the parent and name them as alkyl groups with locants.
Rule: add -yl to the root of the substituent (e.g., methane → methyl; ethane → ethyl).
Example forms: $1$ -methylcyclohexane; $1,1$ -dimethylcyclohexane.

Some substituents have common names (e.g., isopropyl, sec-butyl) and systematic equivalents (e.g., $2$ -propyl, $2$ -methylpropyl).
In exam contexts you may see both; isopropyl alcohol is the common name for $2$ -propanol.
After propyl, butyl, etc., we move beyond basic naming; some common names are still used but systematic names are preferred.

Butyl family has four main isomers: n-butyl, sec-butyl, isobutyl, tert-butyl.
- n-butyl: $1$ -butyl
- sec-butyl: $2$ -butyl
- isobutyl: $2$ -methylpropyl
- tert-butyl: $1,1$ -dimethylpropyl
These bulky groups are denoted with -yl and may appear in naming with locants as needed.

Use the longest chain that gives the most substituents? At minimum, pick the chain that gives the lowest set of locants.
When multiple substitutions exist, number to give the lowest locants (lexicographic lowest set).
If two directions give the same locant set, choose the direction that places the substituent occurring earlier in the alphabet at the lowest number.
Examples: $1$ -ethyl- $2$ -methylcyclohexane vs $2$ -ethyl- $1$ -methylcyclohexane; choose the direction with the lowest set and alphabetical tie-breaker.

Base name: cycloalkane (e.g., cyclohexane).
Substituents receive numbers starting at the substituent to give the lowest locants: 1-, 2-, 3-, …
Example: 1,1-dimethylcyclohexane; 1,3-dimethylcyclohexane; 1-ethyl-2-methylcyclohexane.
When there are several substituents, list them in alphabetical order in the name (ignoring multiplicative prefixes like di-, tri- for the alphabetization).
Alphabetical tie-breaker still applies if needed (e.g., bromo before chloro).

Halogens are named as substituents: chloro-, bromo-, iodo-.
Alphabetize substituents by their names, ignoring di-/tri- etc. for the purpose of ordering.
Example: 1-bromo-2-chloroethane is ordered with both halogens; bromo comes before chloro.

Propane substituents: propyl groups include n-propyl (1-propyl) and isopropyl (2-propyl).
1-methylcyclohexane is the single methyl substituent on cyclohexane.
1,1-dimethylcyclohexane shows two methyls on the same carbon of cyclohexane.
3-ethyl-2-methylcyclohexane shows two different substituents at distinct positions.
Isopropyl alcohol = $2$ -propanol; common vs systematic naming in practice.

Choose parent by longest carbon framework (or ring if appropriate); name substituents with -yl.
Use the lowest set of locants; if tied, use alphabetical order to break ties.
For cycloalkanes, number to give the substituents the lowest possible locants and list substituents alphabetically.
Halogens: use chloro-, bromo-, iodo-; order alphabetically in the name.
Distinguish common vs systematic names (e.g., isopropyl vs 2-propyl; isopropanol vs 2-propanol).