n- | iso- | neo- | sec- or s- | tert- or t- | |
---|---|---|---|---|---|
Stands for | normal | isomer | Greek for new | secondary | tertiary |
Structure | The carbon chain is continuous without any branching; therefore, it represents a straight-chain alkane. | Iso- prefix indicates branching of the straight chain alkane.
The prefix iso- is used when the second carbon of the alkane branch carries one methyl group. So, the terminal isopropyl substituent (CH3)2-CH- refers to the iso- prefix. | Neo-prefix represents a branched-chain alkane.
The prefix neo- is used when the branched chain alkane's second carbon carries two methyl groups. The terminal tert-butyl group (CH3)3-C- refers to the neo substituent. So, a neo-prefix mandatorily requires five carbon atoms or more.
(There is no neobutane. The only isomers of butane are n-butane and isobutane.) | The prefix sec- is used when a functional group is bonded to a secondary carbon of an alkane chain. A secondary carbon has two carbon neighbors.
The sec- prefix is commonly used for four carbon alkyl chains—for example, sec-butyl. At five and above carbon alkyl chains, there is more than one possibility of a functional group being attached to a secondary carbon. Hence, the usage is very limited. | The prefix tert- is used when a functional group is attached to a tertiary carbon of an alkane chain. A tertiary carbon has three carbon neighbours. So, tert-carbon attachments start with four carbon alkyl groups. |
Note : | Note that the prefix iso and neo are used in the common system to distinguish straight-chain alkanes (n-) from branched-chain alkanes of the same molecular formula. | The prefixes sec- and tert- are commonly used to indicate the state of a carbon atom in an alkyl molecule to which a functional group is attached. For example, a primary (10) carbon has one carbon neighbor, secondary (2o) - two, tertiary (3o) -three, and quaternary (4o) - four. | |||
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Functional Groups (if any) | Any functional group, if present, is at the carbon end.
In such instances, the carbon carrying the functional group will get the highest priority (or the lowest number). | If present, the functional group, or any substituent always preserves the terminal (CH3)2-CH- (propyl) unit.
For example, the functional group in iso-propane is at the C-2 carbon to form isopropyl substituent. Similarly, for iso-butyl, the functional group is at C-3 and C-4 for iso-pentyl.
In every case, the numbering prioritizes the functional group over the branching. | The neo- prefix is commonly used for neo-pentane or neo-hexane.
And the associated functional groups are neo-pentyl or neo-hexyl derivatives.
| The functional group is present at the secondary carbon atom of a butane. | The functional group is bonded to a tertiary carbon. |
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Usage in IUPAC | The prefix n - is added to common names and skipped while writing the IUPAC nomenclature. | The i- of the iso is considered while assigning alphabetic priority in IUPAC nomenclature. | The n- of neo- is prioritized while alphabetizing in IUPAC nomenclature. | The prefix sec- is ignored while alphabetizing in IUPAC nomenclature. | The prefix tert- is ignored while alphabetizing in IUPAC nomenclature. |
Examples | Common name- n-Octane IUPAC name- octane | Common name-Isopropyl benzene, Isopropyl alcohol. Corresponding IUPAC names-(propan-2-yl)benzene, propan-2-ol | Common name- Neopentane, Neohexane. Corresponding IUPAC names- 2,2-dimethylpropane, 2,2-Dimethylbutane
| Common name- sec-butylbromide, sec-butanol. Corresponding IUPAC names- 2-bromobutane, 2-butanol. | Common name- tert-butanol, tert-butyl benzene. Corresponding IUPAC name- 2-methyl-2-propanol, 1,1-dimethylethylbenzene. |
Summarizing the differences in one picture-
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