The IUPAC name for the NO₂ molecule is Nitrogen dioxide, while in organic chemistry, the -NO₂ group is typically referred to as a nitro group when attached to a carbon skeleton.
Nitrogen dioxide (NO₂) is an important chemical species, existing both as a free molecule and as a substituent group within more complex compounds. Understanding its nomenclature is key in chemistry.
1. Nitrogen Dioxide as a Molecule
When referring to the inorganic compound NO₂ itself, its IUPAC name is Nitrogen dioxide. This compound is a reddish-brown gas at room temperature and is a prominent air pollutant.
Key Names and Identifiers for NO₂ Molecule:
| Aspect | Detail |
|---|---|
| IUPAC Name | Nitrogen dioxide |
| Other Names | Nitrogen(IV) oxide, deutoxide of nitrogen |
| CAS Number | 10102-44-0 |
Nitrogen dioxide is characterized by its unpaired electron, making it a free radical. It readily dimerizes to dinitrogen tetroxide (N₂O₄) at lower temperatures.
2. The -NO₂ Group as a Functional Group (Nitro Group)
In organic chemistry, when the -NO₂ group is covalently bonded to a carbon atom in a molecule, it is known as a nitro group. Compounds containing this functional group are called nitro compounds. The presence of a nitro group significantly influences the chemical and physical properties of organic molecules.
IUPAC Naming of Nitro Compounds:
According to IUPAC nomenclature, the nitro group is treated as a substituent and is named using the prefix "nitro-". The naming follows these general rules:
- Identify the Parent Hydrocarbon: Determine the longest continuous carbon chain or the parent ring system.
- Number the Chain/Ring: Number the carbon atoms in the parent chain or ring such that the nitro group (and other substituents) receive the lowest possible numbers.
- Prefix "nitro-": Add "nitro-" as a prefix, indicating the position of the nitro group. If multiple nitro groups are present, use di-, tri-, etc., prefixes (e.g., dinitro-, trinitro-).
Examples of Nitro Compounds:
- Nitromethane: CH₃NO₂
- This is the simplest nitro compound, where a nitro group is attached to a methyl group.
- Nitrobenzene: C₆H₅NO₂
- A benzene ring with one nitro group substituent.
- 2,4,6-Trinitrotoluene (TNT): C₆H₂(CH₃)(NO₂)₃
- A well-known explosive, where three nitro groups are attached to a toluene (methylbenzene) ring. The numbers indicate the positions of the nitro groups relative to the methyl group.
Significance of the Nitro Group:
- Electron-Withdrawing: The nitro group is a strong electron-withdrawing group due to the electronegativity of oxygen and nitrogen, and resonance effects. This property impacts the reactivity of the attached molecule, often deactivating aromatic rings towards electrophilic substitution.
- Synthetic Utility: Nitro compounds are important intermediates in organic synthesis. They can be reduced to amines (R-NH₂), which are crucial for forming amides, dyes, and other nitrogen-containing compounds.
- Explosives: Many nitro compounds, especially polynitro compounds, are potent explosives (e.g., TNT, nitroglycerin).
By distinguishing between the free NO₂ molecule and the -NO₂ functional group, we can accurately apply IUPAC naming conventions in both inorganic and organic chemical contexts.
