Why the ortho,meta,para positions are named

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In summary, the terms ortho, meta, and para come from Greek and are used to describe the positions of substituents on a benzene ring. The term meta refers to a state between ortho and para, while ortho refers to two neighboring substituents and para refers to two opposed substituents. The meanings of these terms may seem contradictory, but they are used conventionally to describe different positions on the ring.
  • #1
poolwin2001
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Is there a reason why the ortho,meta,para positions of substituents in the enzene ring named that way?
 
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  • #2
Yes there is a reason, but it is a bit confusing.All three terms come from Greek.

meta is easy - coming from Greek meaning 'among' or in between (as in metastable), is the state in between ortho- and para-.

But the other two seem a little contradictory. Looking at the definition of ortho, one finds:

ortho - straight, upright, vertical (which would see to imply symmetry of a disubstitutional molecule). Or it can refer to perpendicular or right (which is more consistent with the convention).

para - beside, along side of, beyond, aside from.

The last term goes well with the meaning of 'parallel'. However it seems that the third meaning 'beyond' would be consistent with the fact the para- means on the opposite side of.

By convention -

ortho refers to two neighboring substituents
meta refers to two substituents which are separated, but not opposed. It is the state between ortho and para.
para refers to two opposed substituents.
 
  • #3
Thanks.
poolwin2001
 
  • #4
Thanks indeed, Astronuc. This is a great explanation. I had no source on hand to clarify what they really meant.
 

1. Why are the positions ortho, meta, and para used to name compounds?

The positions ortho, meta, and para are used to name compounds because they refer to the relative locations of substituents on a benzene ring. These positions are used instead of the traditional numbering system because they provide more information about the structure and reactivity of the compound.

2. What is the difference between ortho, meta, and para positions?

The difference between ortho, meta, and para positions is the location of the substituents on the benzene ring. Ortho refers to the two adjacent positions, meta refers to the positions that are separated by one position, and para refers to the opposite position.

3. How are ortho, meta, and para positions determined?

The positions of ortho, meta, and para are determined based on the orientation of the substituents on the benzene ring. The relative positions of the substituents can be determined by drawing a line from one substituent to the other and observing the position of the third substituent in relation to this line.

4. Why are ortho, meta, and para positions important in organic chemistry?

Ortho, meta, and para positions are important in organic chemistry because they affect the reactivity and properties of compounds. The different positions can have different effects on the stability, acidity, and basicity of the compound, which can impact its reactions and applications in various industries.

5. Can the ortho, meta, and para positions change in a compound?

Yes, the ortho, meta, and para positions can change in a compound. This can occur through various reactions, such as electrophilic aromatic substitution, which can rearrange the positions of the substituents on the benzene ring. However, these positions are often used as a reference point in organic chemistry and are typically maintained throughout reactions and naming conventions.

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