Organic Nomenclature

The name of organic compounds consists of up to four parts:
1)	Root – longest carbon chain
2)	Primary suffix – type of hydrocarbon (alkane, alkene, alkyne)
3)	Secondary suffix – functional group of highest priority
4)	Prefix – branches (alkyl groups) and functional groups of low priority)

Thus, the name of an organic compound can be obtained by writing the word root, prefixes and suffixes in the following order as per rules described.
Secondary prefix + Primary prefix + Word root + Primary suffix + Secondary suffix.
Root

The root is based on the longest continuous carbon chain. The roots are as follows:

Number of Carbon	Root		Number of Carbon	Root	
1	Meth		16	Hexadec	
2	Eth		17	Heptadec	
3	Prop		18	Octadec	
4	But		19		
5	Pent		20	Eios	
6	Hex		21		
7	Hept		22	Docos	
8	Oct		23		
9	Non		24	Tetracos	
10	Dec		25		
11	Undec		26	Hexacos	
12	Dodec		27		
13			28	Octacos	
14	Tetradec		29		
15			30	Triacont	

Primary suffix
A primary suffix is added to the word root (i.e., at the end of the word root) to indicate whether the parent chain is a saturated or unsaturated. Some primary suffixes are given below.
•	Saturated - ane
•	Unsaturated with: one double bond - ene
two double bonds - diene
three double bounds - triene
•	Unsaturated with: one triple bond - yne
Two triple bond - diyene
Primary suffix on appropriate word root for some typical compounds are:
 Formula of the organic compound	 ‘C’ - atoms in parent chain	 Word root	 Primary suffix	 IUPAC name	
 CH3CH2CH2CH3	 4	 But	 ane	 Butane	
 CH3CH= CH2	 3	 Prop	 ene	 Propene	
 CH≡ CH	 2	 Eth	 yne	 Ethyne	
 CH2 = CH - CH = CH2	 4	 Buta*	 diene	 Butadiene	
 HC≡ C - C≡ CH	 4	 Buta*	 diyne	 Butadiyne	
 
* An extra 'a' has been added to the word root since the primary suffix i.e., diene or diyne begins with consonant i.e., 'd' instead of a vowel as is the case in the first three cases.

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.
Priority	Functional group	Formula	Prefix	Suffix		Priority	Functional group	Formula	Prefix	Suffix	
1	Cations
   e.g. Ammonium	 
–NH4+	-onio-
ammonio-	-onium
-ammonium		8	Hydroperoxides	–OOH	hydroperoxy-	-hydroperoxide	
2	Carboxylic acid	–COOH	carboxy-	-oic acid*		9	Amines	–NH2 	amino-	-amine	
3	Carboxylic acid derivatives
   Esters
   Amides	 

–COOR
–CONH2	 oxycarbonyl-
carbamoyl-	-oate
-amide*		10	Ethers	–O–	-oxy-	 	
4	Nitriles	–CN	cyano-	-nitrile*		11	Peroxides	–OO–	-peroxy-	 	
5	Aldehydes	–CHO	formyl-	-al*							
6	Ketones	>CO	oxo-	-one							
7	Alcohols	–OH	hydroxy-	-ol							
*Note: These suffixes, in which the carbon atom is counted as part of the preceding chain, are the most commonly used. See individual functional group articles for more details.

Secondary suffix
Secondary suffix is used to indicate the function group in the organic compound. Secondary suffixes for various functional groups are given in the table below.
 Family of organic compounds   	 Functional group 	 Secondary suffix 	
 IUPAC names 	 Trivial names 	 	 	 	
 Alkanols	 Alcohols	 (ROH)	 - OH	 -ol	
 Alkanals	 Aldehydes	 (RCHO)	 - CHO	 -al	
 Alkanones	 Ketones	 (RCOR')	 >C = O	 -one	
 Alkanoic acids	 Carboxylic acids	 (RCOOH)	 - COOH	 -oic acid	
 Alkanmides	 Acid amides	 (RCONH2)	 - CONH2	 -amide	
 Alkanoyl chlorides	 Acid chlorides	 (RCOCl)	 - COCl	 -oyl chloride	
 Alkyl alkanoates	 Esters	 (RCOOR')	 - COOR	 -alkyl...oate	
 Alkanenitriles	 Cyanides	 (RCN)	 - CN	 nitrile	
 Alkanthiols	 Thioalcohols	 (RSH)	 - SH	 thiol	
 Alkanarnines	 Amines	 (RNH2)	 - NH2	 amine	

Secondary suffix is written after the primary suffix. While doing so, the following rules should be followed.
•	If the secondary suffix begins with a vowel, then the terminal e of the primary suffix is dropped before adding the secondary suffix.
•	If the secondary suffix begins with a consonant, then the last (terminal) e is retained and the secondary suffix is added after e.
•	If the secondary suffix has some numerical prefix, such as, di, tri etc., before it then the terminal e of the primary suffix is retained.
The addition of the secondary suffix to the primary suffix is illustrated as:
Formula of compound	C - atoms (parent chain)	Word root	Primary suffix	Secondary suffix	IUPAC name	Remarks	
CH3CH2CH2COOH	4	But	ane	Oic acid	Butaroic acid	'e' of primary suffix removed	
CH3CH2CN	3	Prop	ane	Nitrile	Propenenitrile	'e' of primary suffix not removed	
  
  CH2 - OH
   |
  CH2 - OH	2	etn	ane	Diol	Etharediol	'e' of primary suffix not removed	

Prefix
Prefix is a part of the name, which appears before the word root. There are two types prefixes:
Primary prefix
A primary prefix is used to distinguish alicyclic (aliphatic cyclic compounds) from acylic compounds. A prefix cyclo is used before the word root if the compound is an alicyclic compound. For example, Cyclobutane: 

H2C – CH2
     l     l
H2C – CH2 

If the prefix cyclo is absent, in an acylic compound it indicates an open chain compound. 

Secondary prefix
In the IUPAC system of nomenclature, groups are not considered as functional groups (which are indicated by secondary suffixes) but as substituents. Each such group (or substituent) is denoted by a secondary prefix. Some typical secondary prefixes are:
Substituent group 	Secondary prefix 		Substituent group	Secondary prefix	
- F	Fluoro		(CH3)3C -	t-butyl	
- Cl	Chloro		- NO2	nito	
- Br	Bromo		- NH2	amino	
- I	lodo		- NO	nitroso	
CH3 -	Methyl		- N ≡ N +	diazo	
C2H5	Ethyl		- OCH3	methoxy	
CH3CH2CH3 -	n-propyl		- OC2H5	ethoxy	
(CH3)2CH -	iso-propyl		- OR	alkoxy	
 
Groups such as -NO2, -OR, -F, -Cl, -Br and -I are considered as substituents and are indicated by the prefixes. Groups such as -CHO, -CO, -COOH, -COCl, -CONH2, -COOR, -NH2, -CN and -OH are considered as functional groups and are indicated by suffixes.
The following rules should be observed while adding a secondary prefix.
•	In the case of alicylic compounds (aliphatic cyclic), the secondary prefix is added before the primary prefix (before the word cyclo), in the alphabetical order.

       CH2      Bromocyclopropane
      /    \
H2C – CHBr

 

•	In the case of open chain compounds (acyclic), the secondary prefix is added just before the word root in the alphabetical order.
Nitromethane : CH3NO2