Order of Precedence of Groups
When compounds contain more than one functional group, the order of precedence determines which groups are named with prefix or suffix forms. The highest precedence group takes the suffix, with all others taking the prefix form. However, double and triple bonds only take suffix form (-en and -yn) and are used with other suffixes.
Prefixed substituents are ordered alphabetically (excluding any modifiers such as di-, tri-, etc.), e.g. chlorofluoromethane, not fluorochloromethane. If there are multiple functional groups of the same type, either prefixed or suffixed, the position numbers are ordered numerically (thus ethane-1,2-diol, not ethane-2,1-diol.) The N position indicator for amines and amides comes before "1", e.g. CH3CH(CH3)CH2NH(CH3) is N,2-dimethylpropanamine.
| Priority | Functional group | Formula | Prefix | Suffix |
|---|---|---|---|---|
| 1 | Cations e.g. Ammonium |
NH4+ |
-onio- ammonio- |
-onium -ammonium |
| 2 | Carboxylic acids
|
–COOH –COSH –COSeH –SO3H –SO2H |
carboxy- sulfanylcarbonyl- selanylcarbonyl- sulfo- sulfino- |
-oic acid* -thioic S-acid* -selenoic Se-acid* -sulfonic acid -sulfinic acid |
| 3 | Carboxylic acid derivatives
|
–COOR –COX –CONH2 –CON=C< –C(=NH)NH2 |
R-oxycarbonyl- halocarbonyl- carbamoyl- -imido- amidino- |
-R-oate -oyl halide* -amide* -imide* -amidine* |
| 4 | Nitriles Isocyanides |
–CN –NC |
cyano- isocyano- |
-nitrile* isocyanide |
| 5 | Aldehydes Thioaldehydes |
–CHO –CHS |
formyl- thioformyl- |
-al* -thial* |
| 6 | Ketones
|
=O =S =Se =Te |
oxo- sulfanylidene- selanylidene- tellanylidene- |
-one -thione -selone -tellone |
| 7 | Alcohols
|
–OH –SH –SeH –TeH |
hydroxy- sulfanyl- selanyl- tellanyl- |
-ol -thiol -selenol -tellurol |
| 8 | Hydroperoxides
|
-OOH -SOH -SSH |
hydroperoxy- hydroxysulfanyl- disulfanyl- |
-peroxol -SO-thioperoxol -dithioperoxol |
| 9 | Amines Imines Hydrazines |
–NH2 =NH –NHNH2 |
amino- imino- hydrazino- |
-amine -imine -hydrazine |
| 10 | Ethers Thioethers Selenoethers |
–O– –S– –Se– |
-oxy- -thio- -seleno- |
|
| 11 | Peroxides Disulfides |
–OO– –SS– |
-peroxy- -disulfanyl- |
Read more about this topic: IUPAC Nomenclature Of Organic Chemistry
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